ALBERT

Description: Homogenous liquid precursor for ZrC – SiC was prepared by blending of Zr ( OC 4 H 9 ) 4 and Poly[(methylsilylene)acetylene]. This precursor could be cured at 250°C and converted into binary ZrC – SiC composite ceramics upon heat treatment at 1700°C. The pyrolysis mechanism and optimal molar ratio of the precursor were investigated by XRD. The morphology and elements analyses were conducted by SEM and corresponding energy-dispersive spectrometer. The evolution of carbon during ceramization was studied by Raman spectroscopy. The results showed that the precursor samples heat treated at 900°C consisted of t- ZrO 2 (main phase) and m- ZrO 2 (minor phase). The higher temperature induced phase transformation and t- ZrO 2 converted into m- ZrO 2 . Further heating led to the formation of ZrC and SiC due to the carbothermal reduction, and the ceramic sample changed from compact to porous due to the generation of carbon oxides. With the increasing molar ratios of C / Zr , the residual oxides in 1700°C ceramic samples converted into ZrC and almost pure ZrC – SiC composite ceramics could be obtained in ZS-3 sample. The Zr , Si , and C elements were well distributed in the obtained ceramics powders and particles with a distribution of 100 ~ 300 nm consisted of well-crystallized ZrC and SiC phases.

Description: Ce -doped BaTiO 3 -based ceramics were prepared and studied to satisfy ultra-broad temperature stability (from −55°C to 300°C, capacitance variation rate based on C 20°C is within ±15%). The sample with 0.6 mol% CeO 2 succeeds to achieve this performance with a remarkably high ceiling temperature of 300°C. Meanwhile, the sample has good dielectric and electrical properties at room temperature (ε r  = 1667, tanδ = 1.478%, ρ V  = 5.9 × 10 12  Ω·cm). Ce ion can substitute for Ti ion as Ce 4+ or Ba ion as Ce 3+ . The substitution decreases the spontaneous polarization of BaTiO 3 , and then weakens the ferroelectricity of BaTiO 3 . As a result, the temperature stability of samples is improved obviously. Besides, CeO 2 addition promotes the formation of exaggerated grains, which are consisting of Ba 6 Ti 17 O 40 .

Description: This study aims to optimize quantitative X-ray diffraction (XRD) mineralogical analysis of the minority phases in clinker. The proposed method consists of applying Rietveld quantitative refinement to the XRD patterns for both clinker and the insoluble residue remaining after it is attacked with methanol and salicylic acid (Takashima method). The method was tested with industrial clinker and the same material after modifying its mineralogy by refiring at 1500°C followed by slow cooling. The findings showed that the C 4 AF / C 3 A ratios for quickly and gradually cooled clinker were much higher when the clinker diffractograms were refined with the Rietveld procedure than when the proposed method was used. The proportion of C 3 A found with the proposed method was ≈2.8-fold higher than when Rietveld only was applied to the diffractograms for clinkers. Taken together, the refinement data for the two materials (clinker and Takashima residua) revealed that Rietveld quantitative XRD applied to clinker underestimates the low C 3 A content. These findings are supported by postsulfate attack durability studies conducted on cements prepared with the two clinkers.

Description: The effect of increasing poling fields on the properties of (1− x )BZT– x BCT compositions across the morphotropic phase boundary (MPB) is studied using large signal polarization and strain, small signal permittivity and piezoelectric coefficient, and XRD measurements. Successive poling causes charge carrier migration inducing an internal bias field, which becomes large with respect to the coercive field resulting in biased ferroelectric and ferroelastic switching. Improvements in piezoelectric coefficient of 9% are significantly smaller in the tetragonal 60BCT composition compared with the improvement of approximately 50% in the rhombohedral 40BCT and MPB 50BCT compositions. While the properties continue to change with increased poling fields, the remnant ferroelastic domain texture parallel to the field direction, as observed from XRD, stays approximately constant. The improvement in overall domain alignment leading to largely enhanced intrinsic piezoelectricity originates from the alignment of 180° domains and possibly non-180° domains in grains with orientations inclined to the electric field. As a result, poling is most effective in BZT–BCT materials that have low coercive fields, show low distortions and possess more polarization orientations, such as compositions in the rhombohedral phase field or near the MPB.

Description: The defect chemistry-modulated dielectric properties of dense yttria-doped zirconia ceramics prepared by conventional sintering (at 1350°C–1500°C) and electric field-assisted flash sintering (55 V/cm at 900°C) were studied by impedance spectroscopy. While the bulk dielectric properties from both sets of samples showed only small and insignificant changes in conductivity and permittivity, respectively, a huge increase of these properties was measured for the grain boundaries in the flash sintered specimens. A close analysis of these results suggests that flash sintering reduced grain-boundary thickness (by about 30%), while increasing the concentration of oxygen vacancies near these interfaces (by about 49%). The underlying mechanism proposed is electric field-assisted generation and accommodation of defects in the space-charge layers adjacent to the grain surface. The changes in measured permittivity are attributed to the boundary thickness effect on capacitance, while conductivity involved variations in its defect density-dependent intrinsic value, accounting for changes also observed in grain-boundary relaxation frequencies. Therefore, in terms of modifications to the specific dielectric properties of these materials, the overall consequence of flash sintering was to considerably lower the semi-blocking character of the grain boundaries.

Description: This article presents a detailed study on the nanoscaled interface between microelongated gold particles (GP) and biphase leucite/feldspar glass-ceramic matrix. The glass-ceramic composite with a nonuniform GP distribution was processed through hot-pressing under vacuum using a commercial dental ceramic furnace for glass-ceramic dental crown manufacturing. Heat treatments at 900°C, 1100°C, and 1300°C were conducted, and microstructural features along the interface were used to verify the chemical reactions between GP and glass-ceramic matrix. It was observed that the amorphous glass-ceramic matrix had nanoscaled biphase structures, and the distributed nanoscaled amorphous leucite phase was attracted to GP during hot-pressing, and was more reactive with GP than the feldspar phase. The thickness of the interfacial phase formed through chemical reactions between GP and glass-ceramic matrix is around 30 nm. The chemically bonded interface has contributed significantly toward the substantial improvements in both strength and toughness of the GP-reinforced glass-ceramic matrix composite. Characterization techniques, including X-ray diffraction and field-emission scanning electron Microscopy, incorporating X-ray microanalysis using energy dispersive spectrometry, have been employed in this study.

Description: Recent investigations have revealed the great potential of Raman spectroscopy for the characterization of clinker minerals and commercial Portland cements. The usefulness of this technique for the identification of anhydrous, hydrated, and carbonated phases in cement-based materials has been demonstrated. In the present work, the application of micro-Raman spectroscopy for the characterization of the main clinker phases of calcium aluminate cements and calcium sulfoaluminate cement is explored. The main stable hydrated phases as well as several important carbonated phases are investigated. Raman measurements on the following phases are reported: (i) pure, unhydrated phases: CA, C 12 A 7 , CA 2 , C 2 AS, cubic- C 3 A , C 4 AF, and C 4 A 3 ; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet ( C 3 AH 6 ); (iii) carboaluminate phases: hemicarboaluminate and monocarboaluminate. The present results, which are discussed in terms of the internal vibrational modes of the aluminate, carbonate, and sulfate molecular groups as well as stretching O–H vibrations, show the ability of Raman spectroscopy to identify the main hydrated and unhydrated phases in the aluminate and sulfoaluminate cements. The Raman spectra obtained in this work provide an extended database to the existing data published in the literature.

Description: Acmite ( NaFeSi 2 O 6 ) films were formed on steel coupons via solvothermal reaction of silica, sodium hydroxide, and 1, 4-butanediol in an autoclave under autogenous pressure. Systematic variation in processing variables led to homogenous coatings comprised of pinacoidal acmite grains with an average grain size of ~33 μm. The coatings were produced on the steel coupons from reactant conditions of 0.635 m SiO 2 , 2.546 m NaOH , and 3.087 m 1,4-butanediol for 72 h at 240°C.

Description: A 50:50 vol% MgO – Y 2 O 3 nanocomposite with ~150 nm grain size was prepared in an attempt to make 3–5 μm infrared-transmitting windows with increased durability and thermal shock resistance. Flexure strength of the composite at 21°C is 679 MPa for 0.88 cm 2 under load. Hardness is consistent with that of the constituents with similar grain size. For 3-mm-thick material at 4.85 μm, the total scatter loss is 1.5%, forward scatter is 0.2%, and absorptance is 1.8%. Optical scatter below 2 μm is 100%. Variable intensity OH absorption (~6% absorptance) is observed near 3 μm. The refractive index is ~0.4% below the volume-fraction-weighted average of those of the constituents. Thermal expansion is equal to the volume-fraction-weighted average of expansion of the constituents. Specific heat capacity is equal to the mass-fraction-weighted average of heat capacities of the constituents. Thermal conductivity lies between those of the constituents up to 1200 K. Elastic constants lie between those of the constituents. The Hasselman mild thermal shock resistance parameter for the composite is twice as great as that of common 3–5 μm window materials, but half as great as that of c -plane sapphire.

Description: In this work, novel Y 2 Si 2 O 7 / ZrO 2 composites were developed for structural and coating applications by taking advantage of their unique properties, such as good damage tolerance, tunable mechanical properties, and superior wear resistance. The γ- Y 2 Si 2 O 7 / ZrO 2 composites showed improved mechanical properties compared to the γ- Y 2 Si 2 O 7 matrix material, that is, the Young's modulus was enhanced from 155 to 188 GPa (121%) and the flexural strength from 135 to 254 MPa (181%); when the amount of ZrO 2 was increased from 0 to 50 vol%, the γ- Y 2 Si 2 O 7 / ZrO 2 composites also presented relatively high facture toughness (〉1.7 MPa·m 1/2 ), but this exhibited an inverse relationship with the ZrO 2 content. The composition–mechanical property–tribology relationships of the Y 2 Si 2 O 7 / ZrO 2 composites were elucidated. The wear resistance of the composites is not only influenced by the applied load, hardness, strength, toughness, and rigidity but also effectively depends on micromechanical stability properties of the microstructures. The easy growth of subcritical microcracks in Y 2 Si 2 O 7 grains and at grain boundaries significantly contributes to the macroscopic fracture toughness, but promotes the pull-out of individual grains, thus resulting in a lack of correlation between the wear rate and the macroscopic fracture toughness of the composites.

Description: The as-prepared BiFeO 3 ceramic shows a piezoelectric d 33 coefficient of −14 pC/N, that is, an obvious ferroelectric self-poling phenomenon. The temperature gradient between the two surfaces of BiFeO 3 ceramic was intentionally enlarged when BiFeO 3 was prepared with a rapid liquid sintering method. This temperature gradient and the corresponding thermal strain can introduce defect dipoles through separating bismuth vacancies from oxygen vacancies. A mass of these dipoles introduce a macroscopic internal electric field ( E in ) which downward poles BiFeO 3 ceramic during its cooling down process. As expected, an E in of 〉10 kV/cm is confirmed by the asymmetrical polarization/strain versus electric field curves.

Description: The effect of Ba content on the stress sensitivity of the antiferroelectric to ferroelectric phase transition in ( Pb 0.94− x La 0.04 Ba x )[( Zr 0.60 Sn 0.40 ) 0.84 Ti 0.16 ] O 3 ceramics is investigated through monitoring electric field-induced polarization and longitudinal strain under compressive prestresses. It is found that incorporation of Ba significantly suppresses the stress sensitivity of the phase transition, as manifested by slight decreases under prestresses up to 100 MPa in the maximum polarization ( P m ) and longitudinal strain ( x m ). The energy storage density is even increased under the mechanical confinement in compositions x  = 0.02 and 0.04. X-ray diffraction, transmission electron microscopy, and dielectric measurements indicate that the suppressed stress sensitivity is associated with the disruption of micrometersized antiferroelectric domains into nanodomains and the transition from antiferroelectric to relaxor behavior.

Description: Powders and nanoceramics composed of composites of CoFe 2 O 4 , CoFe 2 , and a small amount of FeO were prepared by heating CoFe 2 O 4 powder in reducing atmosphere and by sintering the product of reducing reaction at 350°C via spark plasma sintering technology. In the powders, increase in the molar ratios of CoFe 2 : CoFe 2 O 4 and a great change in magnetic parameters were observed with the change in heating temperature from 300°C to 400°C, and the dominance of dipole interaction over exchange coupling in the interparticle interactions was confirmed by the steps in magnetic hysteresis loops and the negative Henkel plots. However, in the nanoceramics, significant enhancement in exchange coupling was found when the sintering temperature was raised to 500°C and 650°C, which was confirmed by both the positivity of Henkel plot and the single-phase style of the magnetic hysteresis loop.

Description: Gas adsorption porosity measurement of geopolymers (GPs) is required for quantitative understanding of such mesoporous structures, but the complex nature of the GP system makes analysis difficult. Previous results in the literature are often ambiguous or contradictory. A systematic investigation of metakaolin GP gas adsorption results was conducted to optimize the use of this measurement technique and verify that results match known theory about GP structure. It was found that GP undergoes structural change upon degassing at 100°C or higher. If and only if this change is prevented by degassing at a lower temperature could it be shown that specific surface area and total gas adsorption increases with both increasing curing temperature and decreased Si : Al ratio. This observation is consistent with previous suggestions of increased zeolitic character under these conditions, where previous gas adsorption investigations had not observed this expected relationship. Hydrogen physisorption is proposed as a substitute technique for micropore isotherms in GPs due to the difficulty of removing trace gasses from GPs and the measurement effect of such gasses at high vacuum. A hydrogen physisorption isotherm qualitatively resembled an equivalent nitrogen micropore isotherm.

Description: In this work, the role of europium doping of glasses formulated in the ternary system ZnO – CdO – TeO 2 is described. The Eu -doped oxide glasses were prepared by the conventional melt-quenching method and by using three different compositions. Structural studies reveal that there exists a good affinity between Cd and some rare earth (RE) ions to form the crystalline phase. The X-ray diffraction (XRD) diagrams display that the structure of these glasses is amorphous and with the increase in CdO content and the compatibility of Eu 3+ , there is a tendency to form nanocrystals of CdTe 2 O 5 . The scanning electron microscopic (SEM) observation of their microstructure confirms the presence of phase separation. Differential thermal analysis (DTA) of these glasses showed small exothermic peaks noted around 450°C for the V2 glass and 480°C for V1 and V3 glasses, which could be attributed to the formation of these crystals. The infrared spectra showed a main absorption band around 800–600 cm −1 corresponding to the Te – O stretching mode in TeO 4 and TeO 3 groups. By optical absorption (OA), the band gap ( E g ) for each glass was determined; these values were 3.27, 3.14, and 3.3 eV for the V1–V3 glasses, respectively. Furthermore, the presence of Eu 3+ was detected in the 370–470 nm short-range wavelengths. The photoluminescence (PL) experiments of the glasses showed light emission due to the following transitions: 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3, and 5D0 → 7F4.

Description: The conductivity of nominal CaWO 4 , CaW 0.99 Ta 0.01 O 4–δ , 0.7( CaWO 4 )–0.3( La 0.99 Ca 0.01 NbO 4–δ ), and Ca 0.9 La 0.1 WO 4+δ has been studied by means of a.c. impedance measurements. Proton conductivity was observed for CaW 0.99 Ta 0.01 O 4–δ , which displayed exothermic hydration with enthalpy and entropy of –82 kJ/mol and –120 J/molK, respectively. The proton mobility in CaW 0.99 Ta 0.01 O 4–δ was low, with enthalpy and preexponential factor of mobility of 82 kJ/mol and 0.7 cm 2 K/Vs. The high enthalpy of mobility is interpreted to reflect association between the acceptor dopant and protonic defects, whereas the low preexponential factor of mobility may reflect a lower proton concentration than assumed. Rietveld refinement indicated low solubilities of La on Ca -site and Ta on W-site. Proton conductivity was also observed in undoped CaWO 4 , however, not in Ca 0.9 La 0.1 WO 4+δ . The conductivity of 0.7( CaWO 4 )–0.3( La 0.99 Ca 0.01 NbO 4–δ ) behaved much like that of undoped LaNbO 4 , likely due to a very low acceptor dopant concentration.

Description: A new lead-free BNT-based piezoelectric ceramics of (1 −  x ) Bi 0.5 Na 0.5 TiO 3 – x Bi ( Al 0.5 Ga 0.5 ) O 3 ( x  = 0, 0.02, 0.03, 0.04, and 0.05) were synthesized using a conventional ceramic fabrication method. Their structures and electrical properties were investigated. All the samples show a typical ferroelectric P ( E ) loops and S ( E ) curves at room temperature. The optimal properties are obtained at the composition of the x  = 0.03. The substitution of Bi ( Al 0.5 Ga 0.5 ) O 3 enhances piezoelectric constant and increases Curie temperature from 58 pC/N and 310°C of pure BNT to 93 pC/N and 325°C of the x  = 0.03. The temperature-dependent P ( E ) loops and S ( E ) curves of 0.97BNT–0.03BAG indicate that phase transition from ferroelectric to antiferroelectric takes place over a very wide temperature region from 80°C to 180°C. The results show that the introduction of BAG improves the electrical properties of BNT.

Description: We studied ancient enamels on gilded copper from a collection of archeological horse harness pendants of the Museo Instituto Valencia de Don Juan (Madrid, Spain) to test the benefits of a new, nondestructive analytical methodology based on chemometric analysis (i.e., Principal Component Analysis, PCA) on micro-ATR-FTIR spectral data and chemical quantification using SEM-EDS. The novelty of this approach was threefold: (i) PCA allowed the discrimination of the different harness pendants of known origin and attributed to the 14th and 15th centuries according to the chemical complex composition, nanostructure, glass weathering, and/or coloring mechanisms of each colored enamel, separately (i.e., red, purple, blue, and white), (ii) it is a cheap, easily available and nondestructive methodology that enables us to (iii) draw archeological conclusions about the quality of the manufacturing process, reassess the chronology of these objects and attempt to attribute them to different workshops according to the different traditional recipes identified. In particular, the enamels were made of alkali and/or alkaline earth lead-glass with a wide range of chemical compounds in the form of pigments or opacifiers. Two types of coloring mechanisms were identified, colloidal particles such as copper-ruby for red enamels, and ionic mechanisms such as Fe (II) and Co (II) to achieve a blue pigments; Mn (III) in the purple pigment; and two kind of white enamels were identified, i.e., tin oxide as an opacifier and uranium oxide. In addition, we established the reason for the poor state of conservation of some of the enamels by means of the identification of depolymerization and ion exchanges, well-known harmful effects of glass weathering, and finally a chronology was assigned for some of these pieces according to the enamel composition.

Description: Novel glass-ceramics with embedded thermoelectric Bi 2 Se 3 crystals were prepared from glass matrices in the Ge 20 Se 100− x Bi x ( x  = 5, 10, 12 mol%) system. Based on DSC results performed at different heating rates, characteristic activation energies ( E c ) and Avrami exponents ( n ) were obtained and analyzed by using Kissinger's relation, Ozawa's method, Augis–Bennett approximation and Matusita–Sakka theory. XRD results showed that pure Bi 2 Se 3 crystalline phase precipitated upon annealing at different temperatures for various time. The crystal size and crystalline fraction in the samples could be tuned by controlling the annealing time.

Description: In the present investigations nano size high alumina cements (HAC) were prepared by very effective co-melt precursor sintering technique from their metal nitrate precursors. The prime cementing phases observed were CA, CA 2 , and C 12 A 7 . The addition of nano structured cements in refractory castables has improved the thermo-chemical-mechanical properties to a significant extent. Each batch of low cement castables (LCC) was prepared from calcined Chinese bauxite, HAC, and superfine additives. The effect of HAC in bauxite castable with the additives similar to Silicon Carbide, reactive alumina, and micro-fine silica on the sinterability and properties of these castables was investigated. Physical properties such as apparent porosity and bulk density, mechanical properties such as hot modulus of rupture (HMOR), cold and hot modulus of rupture (CMOR), and cold crushing strength (CCS) of hydrated and sintered castables were studied. The sintered castables were also characterized for their solid phase compositions and microstructure using X-ray diffraction (XRD) and FE-SEM, respectively. In the castables new phases such as mullite, α-alumina were formed at the expense of bauxite and silica. Solid solution of mullite formed at high temperature acts as a bonding phase and is accounted for high HMOR, CMOR, and CCS values. These excellent properties of such castables may enable their uses in various applications such as refractory lining for fabrication of steel, aluminium, copper, glass, cement, chemicals, and ceramics.

Description: Zn 2 GeO 4 ceramic materials were synthesized by the solid-state method. Zn 2 GeO 4 powders were investigated with X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Oxygen defects in the Zn 2 GeO 4 ceramics were investigated by photoluminescence, Raman, and EDS spectra. Conductivity of Zn 2 GeO 4 was 0.18 S/cm at low temperature of 773 K, and its activation energy was 0.49 eV. The results showed that Zn 2 GeO 4 was a promising low-temperature electrolyte with high conductivity.

Description: This article details the influence of zirconium doping on the piezoelectric properties and relaxor characteristics of 94( Bi 1/2 Na 1/2 ) TiO 3 –6 Ba ( Zr x Ti 1− x ) O 3 (BNT–6BZT) bulk ceramics. Neutron diffraction measurements of BNT–6BZT doped with 0%–15% Zr revealed an electric-field-induced transition of the average crystal structure from pseudo-cubic to rhombohedral/tetragonal symmetries across the entire compositional range. The addition of Zr up to 10% stabilizes this transition, resulting in saturated polarization hysteresis loops with a maximum polarization of 40 μC/cm 2 at 5.5 kV/mm, while corresponding strain hysteresis measurements yield a maximum strain of 0.3%. With further Zr addition, the ferroelectric order is progressively destabilized and typical relaxor characteristics such as double peaks in the current density loops are observed. In the strain hysteresis, this destabilization leads to an increase of the maximum strain by 0.05%. These changes to the physical behavior caused by Zr addition are consistent with a reduction of the transition temperature T F-R , above which the field-induced transformation from the relaxor to ferroelectric state becomes reversible.

Description: Precursor glasses for the ferroelectric barium bismuth titanate ( BaBi 4 Ti 4 O 15 ) (BBiT) have been prepared by the melt-quench technique in the SiO 2 – K 2 O – BaO – Bi 2 O 3 – TiO 2 (SKBBT) glass system with and without Eu 2 O 3 doping. BBiT glass–ceramic (GC) nanocomposites have been derived from these glasses by controlled heat treatment. The structural properties of the GCs have been investigated using X-ray diffraction (XRD), electron microscopy (FE-SEM, TEM), and FT-IR reflectance spectroscopy. FE-SEM images show the formation of randomly oriented hexagonal rod-shaped crystals of 200–400 nm and TEM images show 10–20 nm crystallites. FT-IR spectra exhibit the characteristic bands of BBiT at 480, 585, and 680 cm −1 . The activation energy of crystallization ( E c ) varies from 295 to 307 kJ/mol. The dielectric constants (ε r ) of glass and GC nanocomposites increase with an increase in frequency up to 3.0 MHz and then decrease up to 5.0 MHz. Heat-treated GCs show higher ε r values, in the range 25–55, compared to the precursor glasses (20–37). Dielectric losses (tan δ) for all the samples increase from 0.005 to 1.0 with an increase in frequency from 100 Hz to 5.0 MHz. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5 D 0 → 7 F 2 transition. An intense 466 nm excitation band corresponding to the 7 F 0 → 5 D 2 transition was observed. Emission spectra were then recorded by exciting the glass samples at 466 nm. Longer heat-treatment times led to a 15-fold increase in the intensity of the red emission at 612 nm, attributed to the segregation of Eu 3+ ions into the low phonon energy BBiT crystallites. The hardness (3.8–5.1 GPa) and fracture toughness (1.8–3.5 MPam 0.5 ) values obtained in the GCs are high and suitable for structural applications.

Description: Carbon doping is known to be very effective for enhancing the high-field properties of magnesium diboride, MgB 2 , but not for the low-field properties. Here, we report that both the high- and the low-field properties can be improved simultaneously without doping by increasing the initial magnesium partial pressure, by simply reducing the size of the magnesium particles. It is shown that in situ processed bulk MgB 2 sintered with fine magnesium powders has superior superconducting properties compared with a bulk sample fabricated using coarse magnesium lumps. The change in the lattice parameters was almost negligible; however, a clear increase in lattice strain can be observed for the sample sintered with fine magnesium powders. The increase in the lattice strain results in an enhancement of the high-field properties. Furthermore, it has also been found that the low-field critical current density is not reduced, but rather slightly increased for the fine magnesium powder sample. This is due to a closer linkage among the grains that drastically improves grain connectivity. These findings demonstrate that the initial growth mechanism of MgB 2 is very crucial for its superior superconducting properties, and it especially indicates the importance of magnesium vapor pressure.

Description: Revisiting classic phase diagrams and chemical phase relations in the solid state of a very well-studied oxide system, such as the lithium aluminosilicate (LAS) system, can open a new window for the design of new advanced materials with improved properties. Crystal chemistry and phase equilibria are used to demonstrate the ability to design materials with particular desired properties in the alumina-rich corner of the LAS phase diagram. The experimental results demonstrate the alumina and β-eucryptite solid-state compatibility.

Description: This work reports the crystallization, microstructure, and surface composition of Cu In 0.7 Ga 0.3 Se 2 (CIGS) thin films grown by femtosecond pulsed laser deposition at different annealing temperatures. The structural and optical properties of the CIGS films were characterized by X-ray diffraction, Raman scattering, UV-visible spectroscopy, and Hall effect measurement. The results indicate that binary crystals of CuS e initially formed on the as-deposited film, but then completely turned into a quaternary chalcopyrite structure after annealing at 400°C. Phase transformation significantly affects the surface morphology, Hall properties, and band gap. Transmission electron microscopy further revealed that an interface between the Mo substrate and CIGS crystallites contains an amorphous layer even at the high temperature of 500°C. For the application of photovoltaic devices, we also report on the photoresponse of both as-deposited and annealed films as demonstrated by preliminary tests.

Description: Reactive sintering of 3 Ti : Sn :2 C and 3Ti:Sn:2C:0.6Fe powder mixtures is studied in the temperature range 510°C–1200°C under argon. It is demonstrated that the recently discovered Ti 3 SnC 2 phase is formed, provided that Fe is added to a 3 Ti : Sn :2 C reactant mixture within the synthesis conditions used. Using dilatometric and X-Ray diffraction analyses, the formation mechanism of Ti 3 SnC 2 is discussed. Results show that at low temperature (about 510°C), tin is consumed to form Fe x Sn y intermetallics. At high temperature (about 1060°C), tin is newly available to form Ti 3 SnC 2 due to the melting of Fe x Sn y . Then, the intermediate phases, TiC and Ti 2 SnC , and/or Ti 5 Sn 3 , TiC , C , and Ti are dissolved in the ( Fe  +  Sn ) liquid phase and Ti 3 SnC 2 very likely precipitate from the melt. The second part of the study deals with the optimization of the Fe content in the initial 3Ti:Sn:2C reactant powder mixture to synthesize samples with larger Ti 3 SnC 2 content by hot isostatic pressing.

Description: The effects of non-stoichiometry on the microstructure, oxygen vacancies, and piezoelectric properties of ( Na 0.5 K 0.5 ) x NbO 3 (NK x N, where x  =   0.98, 1.00, 1.01, and 1.02) ceramics doped with sintering aid CuTa 2 O 6 (CT) doping were investigated. X-ray diffraction (XRD) patterns indicated that a secondary phase formed in CT-doped NK x N (NK x NCT) ceramics with x  〈   1.00 and that a pure phase was obtained with x  ≥   1.00. The grain size of NK x NCT ceramics increased with increasing x value due to the formation of a liquid phase. The internal bias field, activation energy, and Raman analysis for NK x NCT ceramics showed that the number of induced oxygen vacancies increased with decreasing x value. The high mechanical quality factor ( Q m ) value obtained for NK x NCT ceramics did not correspond to a higher concentration of oxygen vacancies, illustrating that the suitable compensation (excess Na and K ) is more important than the concentration of oxygen vacancies to obtain the ceramics with high Q m values. The NK x NCT ceramics with x  =   1.01 exhibited excellent piezoelectric properties, with k p and Q m values of 39.9% and 2,070, respectively.

Description: Low-temperature sintering of β-spodumene ceramics with low coefficient of thermal expansion (CTE) was attained using Li 2 O – GeO 2 sintering additive. Single-phase β-spodumene ceramics could be synthesized by heat treatment at 1000°C using highly pure and fine amorphous silica, α-alumina, and lithium carbonate powders mixture via the solid-state reaction route. The mixture was calcined at 950°C, finely pulverized, compacted, and finally sintered with or without the sintering additive at 800°C–1400°C for 2 h. The relative density reached 98% for the sample sintered with 3 mass% Li 2 O – GeO 2 additive at 1000°C. Its Young's modulus was 167 GPa and flexural strength was 115 MPa. Its CTE (from R.T. to 800°C) was 0.7 × 10 −6  K −1 and dielectric constant was 6.8 with loss tangent of 0.9% at 5 MHz. These properties were excellent or comparative compared with those previously reported for the samples sintered at around 1300°C–1400°C via melt-quenching routes. As a result, β-spodumene ceramics with single phase and sufficient properties were obtained at about 300°C lower sintering temperature by adding Li 2 O – GeO 2 sintering additive via the conventional solid-state reaction route. These results suggest that β-spodumene ceramics sintered with Li 2 O – GeO 2 sintering additive has a potential use as LTCC for multichip modules.

Description: Pyrochlore-structured lanthanide stannate ceramic ( Ln 2 Sn 2 O 7 ) has been synthesized via a new complex precipitation method. A suite of characterization techniques, including FTIR, Raman, X-ray, and electron diffraction as well as nitrogen sorption were employed to investigate the structural evolution of the synthesized and calcined powder. Raman, XRD, and selected area electron diffraction results confirm the presence of the pyrochlore structure after calcination of the powder above 1200°C. TEM imaging shows fine crystallites gradually increased in size from approximately 100 nm to about 500 nm with higher calcination temperatures. Grain growth and powder densification upon increasing the calcination temperature was confirmed by nitrogen sorption results. This aqueous synthetic method provides a simple pathway for the preparation of homogeneous lanthanide stannate ceramics.

Description: Ceramics have played a crucial role in the development of fission based nuclear power, in glass & glass composite high level wasteforms, in composite cements to encapsulate intermediate level wastes (ILW) and also for oxide nuclear fuels based on UO 2 and PuO 2 /UO 2 mixed oxides. They are also used as porous filters with the ability to absorb radionuclides (RN) from air and liquids and are playing a key role in the cleanup at Fukushima. Non-oxides also find current fission applications including in graphite moderators and B 4 C control rods. Ceramics will continue to be significant in the near-term expansion of nuclear power via next-step developments of fuels with inert matrices or based on thoria and in wasteforms using alternative composite cements or single or multiphase ceramics that can host Pu & other difficult RN. Longer term advances for Generation IV reactors, which will operate at higher temperatures & with higher fuel burn-up require innovative fuel developments potentially via carbides & nitrides or composite fuel systems. Novel non-thermal (cement-like) and thermal techniques are currently being developed to treat some of the difficult legacy wastes. Non-thermally derived wasteforms developed from geopolymers, composite cements, hydroceramics, and phosphate-bonded ceramics and thermally derived wasteforms made by Hot Isostatic Pressing and fluidized bed steam reforming (FBSR) as well as vitrification techniques based on cold crucible melting (CCM), Joule-heater in-container melting and plasma melting (PM) are described. Future developments in waste treatment will be based on separation technologies for partitioning individual RN along with design & construction of RN-containing ceramic targets for inducing transmutation reactions. Near demonstration actinide-hosting ceramic wasteforms including multiphase Synroc systems are described. Opportunities also exist for ceramics in structural applications in Generation IV reactors such as composite SiC / SiC and C / C for fuel cladding and control rods and MAX phases and ultrahigh-temperature ceramics (UHTCs) may find near core fuel coating and cladding applications. Uses of ceramics in fusion reactor systems will be both functional (ceramic superconductors in magnet systems for plasma control and in Li silicate breeder blankets in tokamaks) and structural including as sapphire diagnostic windows, graphite diverters, and plasma facing C and UHTCs. In all these cases, performance is limited by poorly understood radiation damage and interface controlled processes, which demands a combined modeling/experimental approach.

Description: The promotion of zircon ( ZrSiO 4 ) crystallization by ZnO from a zirconium-based frit glaze was studied and the possible mechanism was discussed. X-ray diffraction was used to analyze the relative quantities of zircon and other transitional crystals in the samples. The results show that ZnO can significantly decrease the crystallization temperature of zirconium-based glaze, depress the formation of Ca 2 ZrSi 4 O 12 , and promote the devitrification of transitional crystals t - ZrO 2 and Ca 2 ZnSi 2 O 7 , as well as lead to the formation of more zircon than the ZnO -free glaze. It was also found that zircon not only can form from the interaction between t - ZrO 2 and SiO 2 but also can devitrify directly from the glass phase of zirconium-based glaze.

Description: Barium-substituted CsAlSi 2 O 6 pollucites, Cs x Ba (1− x )/2 AlSi 2 O 6 , and barium- and iron-substituted pollucites, Cs x Ba (1− x )/2 Al x Fe 1− x Si 2 O 6 and Cs x Ba 1− x Al x Fe 1− x Si 2 O 6 were synthesized with 1 ≥  x ≥ 0.7 using a hydrothermal synthesis procedure. Rietveld analysis of X-ray diffraction data confirmed the substitution of Ba for Cs and Fe for Al , respectively. The crystallographic analysis also describes the effects of three different types of pollucite substitutions on the pollucite unit cell: Ba 2+ for Cs 1+ cation results in little effect on cell dimensions, intermediate concentrations of Ba 2+ and Fe 3+ substitution result in net minor expansion due to Fe 3+ addition, and large Ba and Fe substitutions result in overall framework contraction. Elemental analysis combined with microscopy further supports the phase purity of these new phases. These materials can be used to study the stability of CsAlSi 2 O 6 as a durable ceramic waste form, which could accommodate with time Cs and its decay product, Ba . Furthermore, success in iron substitution for aluminum into the pollucite lattice predicts that redox charge compensation for Cs cation decay is possible.

Description: Nitrogen-doped mullite fibers were first synthesized through the nitridation of Al 2 O 3 – SiO 2 gel fibers in NH 3 . The results showed that nitrogen take-up began at 800°C, reached the maximum at 900°C, and then decreased with increasing temperature. The ceramic fibers nitridated at 900°C were essentially amorphous, but contained a small amount of nano-sized Al – Si spinel crystals. Mullite was formed after nitridation at 1200°C, accompanied by crystallization of χ- SiAlON and δ- Al 2 O 3 . The incorporation of nitrogen resulted in the formation of a variety of nitrogen-containing crystalline phases. The grain size of the mullite fibers can be adjusted by changing of the nitrogen content.

Description: The solubility limit of Ca in 99.99% pure α- Al 2 O 3 (alumina) was measured using a wavelength dispersive spectrometer mounted on a scanning electron microscope. Al 2 O 3 samples were equilibrated at a concentration which ensured saturation of the Al 2 O 3 grains with Ca , and were quenched in water from 1600°C. The results were compared with those from samples which were furnace cooled from 1600°C. For the quenched samples, the Ca solubility limit was found to be 51 ± 1 ppm, which is significantly larger than the solubility limit for samples which were furnace cooled (26 ± 1 ppm).

Description: The possibility of developing large solid oxide fuel cell (SOFC) stacks based upon 25 cm 2 ceramic oxide anode-supported cells is investigated. Planar fuel cells comprising strontium titanate-based anode support impregnated with active catalysts were prepared using a combination of deposition techniques. The fuel cell tests performed in a semisealed rig have shown power densities of 185 mW cm −2 at 850°C using humidified hydrogen as fuel and air as oxidant. The structure and evolution of the catalytically active impregnated materials-10 mol% Gd -doped CeO 2 and nickel- are analysed using electron microscopy at the end of the fuel cell test, revealing that a ceria and nickel layer surrounds the titanate backbone grains while ~50–150 nm spherical-like nickel particles uniformly decorate this top layer.

Description: Structural and dielectric properties of (1− x ) BaTiO 3 – x Bi ( Mg 1/2 Ti 1/2 ) O 3 ( x  = 0.1–0.5) were investigated to understand the binary system and utilize it for high-voltage, high energy density capacitors. The solubility limit for Bi ( Mg 1/2 Ti 1/2 ) O 3 in a BaTiO 3 perovskite was between x  = 0.4 and x  = 0.5. A phase with pseudocubic symmetry was formed for x  = 0.1–0.4; a secondary phase developed at x  = 0.5. Dielectric measurements showed highly diffusive and dispersive relaxor-like characteristics from 10 to 40 mol% of Bi ( Mg 1/2 Ti 1/2 ) O 3 . These compositions also showed high relative permittivity with low-temperature coefficients of permittivity over a wide range of temperatures −100°C–600°C. Relaxation behavior was quantitatively investigated using the Vogel–Fulcher model, which revealed the activation energy of 0.17–0.22 eV. Prototyped multilayer capacitors of 18 mm × 17 mm × 4 mm dimensions with a capacitance of 12.5 nF at 1 kHz were successfully constructed and demonstrated multiple charge–discharge characteristics up to 10 kV.

Description: K 3 Gd ( PO 4 ) 2 : RE 3+ (RE = Eu, Tb) are prepared by solid-state reaction and their photoluminescence (PL) properties are investigated under UV and VUV excitation, respectively. The obtained experimental data show that no energy transfer happens among the activator ions Tb 3+ or Eu 3+ under UV excitation. Under 147-nm excitation, the strongest emission intensity of K 3 Gd ( PO 4 ) 2 : RE 3+ (RE = Eu, Tb) is obtained when the activator ions Tb 3+ or Eu 3+ concentration is 0.8 mol, the integrate emission intensity of K 3 Gd 0.2 (PO 4 ) 2 :0.8Tb 3+ is about 204% of commercial phosphor Zn 1.96 SiO 4 :0.04 Mn 2+ with chromaticity coordinates of (0.340, 0.561) and the decay time of about 5.09 ms under 147-nm excitation. We analyze the experimental data and propose a possible energy-transfer mechanism under 147-nm excitation.

Description: The 0.72 Bi ( Fe 1− x Al x ) O 3 –0.28 BaTiO 3 ( x  = 0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFA x – BT ) lead-free high-temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high-temperature stability of piezoelectric properties was carried out. The crystalline structures of BFA x –BT ceramics evolve from rhombohedral structure with x 〈  0.01 to the coexistence of rhombohedral structure and pseudocubic phases with x  ≈ 0.01, finally to pseudocubic phases when x 〉  0.03. Remarkably high-temperature stability with near-zero temperature coefficient of piezoelectric properties ( TCk p ), together with improved piezoelectric properties has been achieved for x  = 0.01 BFA x –BT ceramics. The BFA x –BT( x  = 0.01) ceramics simultaneously show the excellent piezoelectric properties of d 33  = 151 pC/N, k p  = 0.31 and super-high-temperature stability of T d  = 420°C, TCk p  = 1 × 10 −4 . It is considered that the observed strong piezoelectricity and remarkably high-temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCk p value and the pseudocubic phases possess a negative TCk p value. Thus, the TCk p value of BFA x –BT ceramics can be tuned by composition of x .

Description: Owing to the widespread presence of electromagnetic interferences, it is necessary to develop new materials with excellent high-temperature electromagnetic wave (EM) absorption properties. In the present work, ZnO is infiltrated into porous ZrSiO 4 substrates to form ZnO / ZrSiO 4 composite ceramics using sol-gel process. The doping of aluminum results in the improvement of electrical conductivity and the significant change in the morphology of ZnO . With the increase in environment temperature during measurement, the permittivity of the composite ceramics increases first and then decreases dramatically, which is attributed to the change in conductive loss. The electrical conductivity increases with increasing measurement temperature. However, the concentration of oxygen vacancies decreases under air atmosphere when the measurement temperature increases continuously, which results in the reduction in conductivity. Therefore, permittivities of the undoped and doped ceramics measured at 673 K are higher than the ones at the other temperatures. The composite ceramics maintain a relatively high EM absorption coefficient, low reflection coefficient (RC), and wide effective absorption bandwidth at environment temperatures up to 773 K. As a result, we conclude that the ZnO / ZrSiO 4 composite ceramics exhibit a promising prospect as a kind of high-temperature EM absorbing material.

Description: [0001] textured alumina ceramics with a fine grain size were fabricated between 1400°C and 1600°C via templated grain growth (TGG) using fine alumina platelets (~0.6 and ~3 μm diameter) aligned by tape casting in either a 50 nm α- Al 2 O 3 matrix powder, or in a seeded boehmite sol. The 3 μm templates could be readily aligned by tape casting in both matrices (orientation parameters r  = 0.27 and 0.18, respectively), whereas 0.6 μm diameter templates were well aligned in the seeded boehmite sol only ( r  = 0.29). Improved alignment in boehmite sols is attributed to inorganic gelation, resulting in a strongly pseudo-plastic rheology that preserves template alignment against the influence of Brownian motion. The in situ formation of fine α- Al 2 O 3 matrix after transformation in the seeded boehmite system results in a higher driving force for TGG and improves texture development. The combination of 3 μm templates with a seeded boehmite matrix results in extremely high texture qualities (texture fraction f  = 0.97–0.99, r  = 0.17) while maintaining a relatively fine grain size (5–10 μm in diameter and 1.5–3 μm in thickness). Although undoped samples can be fully textured at 1600°C, adding as little as ~0.25 wt% CaO / SiO 2 dopant improves TGG kinetics and yields full texture at 1400°C.

Description: Yttria partially stabilized zirconia Y-PSZ/glass-ceramic composites were prepared by reaction sintering using powder mixtures of a SiO 2 – Al 2 O 3 – ZnO – CaO – ZrO 2 – TiO 2 -based glass and yttria partially stabilized zirconia (Y-PSZ). The glass crystallized during sintering at temperatures of 1173, 1273, and 1373 K to give a glass-ceramic matrix for high-temperature protecting coatings. With the increasing firing time, the added zirconia reacted with the base glass and a glass-ceramic material with dispersed zircon particles was prepared in situ . Furthermore, the added zirconia changed the crystallization behavior of the base glass, affecting the shape, amount, and distribution of zircon in the microstructure. The bipyramid-like zircon grains with imbedded residual zirconia particles turned out to have two growth mechanisms: the inward growth and the outward growth, and its rapid growth was mainly dominated by the later one. For comparison, the referenced glass-ceramic was prepared by sintering using exclusive glass granules and its crystallization behavior at 1173–1373 K was examined as well. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to characterize the crystallization behavior of the base glass and the phase evolution of the Y-PSZ/glass-ceramic composites.

Description: In this study, we present the preparation of a bulk material with a composition of 80 GeTe 2 –20 Ga 2 Te 3 by combining mechanosynthesis and sintering. This composition cannot be prepared by conventional melt/quenching technique. The progressive evolution of the powder during ball-milling is followed by X-ray Diffraction (XRD) and Differential Scanning Calorimetry analysis. The final powder obtained is highly crystalline, but a glass transition temperature ( T g ) is observed, indicating the presence of some amorphous phase remaining, allowing for its efficient sintering. By hot-pressing, a dense bulk material with a fine microstructure and a high electrical conductivity is obtained. The synthesis method described represents a simple and cost-effective way to produce tellurium-based materials of desired dimension with potential applications for optical storage or thermoelectric devices.

Description: Revealing and understanding the microscopic origins of the macroscopic properties of aluminosilicate glasses is important for the design of new glasses with optimized properties. In this work, we study the composition-structure-property relationships in 20 MgO / CaO sodium aluminosilicate glasses upon Al 2 O 3 -for- SiO 2 and MgO -for- CaO substitutions. We find that some properties (density, molar volume, Young's modulus, and shear modulus) are linear through the investigated range of Al 2 O 3 compositions, while others (refractive index, coefficient of thermal expansion, Vickers hardness, isokom temperatures, and liquid fragility index) exhibit a change in the slope around the composition with [ Al 2 O 3 ] = [ Na 2 O ], which is especially pronounced for the glasses containing MgO . We discuss these phenomena based on structural information obtained by NMR spectroscopy and topological considerations.

Description: In this article the changes on the surface of the 45S5 bioglass submitted to an enrichment with calcium ions were investigated. The method employed was the immersion of bioglass in calcium molten salt bath at 450°C. Changes in composition were probed by different techniques of chemical analysis. The use of SEM-EDS allowed estimating the thickness modified, as being about 10 μm. X-ray photoelectron spectroscopy enabled to infer over the structural changes on the surface of 45S5 bioactive glass. The entry of calcium in the vitreous network promoted the phase separation of microdomains rich in silica and phosphate on the surface of the glass. The formation of immiscibility region was attributed a depolymerization of silica network and also, to a possible migration of phosphate species from the bulk. The results of this study indicate a great change in the surface properties of this biomaterial. In addition, the method proposed in this study proved to be very promising in the possibility of designing the surface of bioactive glasses, to modulate the desired properties, keeping the bulk unchanged.

Description: Lanthanum hexaaluminate is a promising competitor to establish yttria partially stabilized zirconia as a thermal barrier coating material for Ni -based superalloy due to its relative low intrinsic thermal conductivity and low sinterability at temperatures exceeding 1100°C. Sr 2+ and Ti 4+ were selected as two dopants to partially substitute the La 3+ and Al 3+ in LaMgAl 11 O 19 , respectively. The variation in thermal conductivity with Sr 2+ and Ti 4+ fractions was analyzed based on structure information provided by X-ray diffraction and Raman spectroscopy. The average crystal size of LaMgAl 11 O 19 sintered at 1600°C for 10 min by spark plasma sintering is in nanoscale. The fully dense La 1− x Sr x MgAl 11− x Ti x O 19 solid solution showed a minimum thermal conductivity value (λ = 1.12 W/(m K) −1 , T  = 1273 K) at the composition of La 0.5 Sr 0.5 MgAl 10.5 Ti 0.5 O 19 ,which possibly reduces from the enhanced phonon scattering due to mass and strain fluctuations at the Ln 3+ and B 3+ sites.

Description: Aqueous 3Y-TZP inks with solid contents of 22 and 27 vol% were used for fabricating three-dimensional ceramic components by the direct ink-jet printing process (DIP). The DIP fabrication was realized using a thermal ink-jet (TIJ) printing system. Despite the different physical properties of the inks, both inks were successfully ejected and deposited. To define the optimum window of the ink properties required for a stable printing operation, both ceramic inks as well as a typical TIJ ink were characterized in terms of particle size distribution, zeta potential, viscosity, surface tension, and the inverse Ohnesorge number ( Oh −1 ). Moreover, single drops of all inks were deposited and analyzed by scanning electron microscopy (SEM) to examine the form and integrity of the ejected drops. Demonstration objects (a base with curved channels and a sample molar tooth) were DIP fabricated using both of the ceramic inks. These objects show the potentials of the DIP process for ceramics manufacturing particularly by using TIJ printing systems.

Description: Spherical granules of aluminum nitride (AlN) with an average particle size of about 50 μm were produced from aqueous suspensions using an AlN powder surface treated against hydrolysis with aluminum dihydrogenphosphate [Al(H 2 PO 4 ) 3 ]. Two different amounts of Al(H 2 PO 4 ) 3 were tested and the effects of surface treatment and aging time were evaluated by various techniques (XRD, TG-DTA, zeta potential and pH measurements). The treated powder exhibited antihydrolytic property and good dispersing behavior, enabling the preparation of low-viscosity and high-concentration aqueous AlN slurries for freeze granulation. The spherical AlN granules were sintered in a boron nitride (BN) powder bed followed by ultrasonic washing of the AlN granulates/BN mixture to remove BN. The sintered spherical AlN granules present excellent crystallinity and high sphericity as observed from SEM micrographs.

Description: Near-infrared (NIR) quantum cutting involving the emission of two NIR photons for each visible photon absorbed is realized from Eu 2+ /Yb 3+ codoped chalcohalide glasses. Excitation, emission and decay spectra are measured to prove the occurrence of cooperative energy transfer (ET) from Eu 2+ to Yb 3+ . The maximum ET efficiency obtained is as high as 85%. The ET from Eu 2+ to Yb 3+ is followed by dipole-dipole interaction. The possible mechanism of ET is discussed.

Description: Well-crystallized pure BiFeO 3 nanopowders were successfully synthesized at the temperature as low as 120°C by an ethanol-assisted hydrothermal process. In this synthesis, the composition of the solvent played important roles in the formation of pure BiFeO 3 . The BiFeO 3 nanopowders synthesized with 4:3 ethanol/water ratio mainly consists of cubic structures with size from 50 to 150 nm. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements indicated that pure BiFeO 3 nanopowders showed a spin-glass transition below the freezing temperature. Moreover, the BiFeO 3 nanopowders exhibited ferromagnetic order at room temperature.

Description: Nanoparticles of Co 0.6 Zn 0.4 Fe 2 O 4 , with narrow size distribution, regular morphology, and high saturation magnetization, have been synthesized. The synthesis, involved a very rapid mixing of reducible metal cations with sodium borohydride, is carried out in a colloid mill and followed by a separate hydrothermal process. The microstructure and magnetic properties of the synthesized nanoparticles are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The effects of different synthesis conditions (synthesis temperature and reaction time) on the characteristics of the ferrite nanoparticles are discussed. The changes in cation contribution are revealed by the Raman study. The magnetic measurements explore that all the as-synthesized samples are superparamagnetic in nature. The corresponding superparamagnetic behavior is explained by paramagnetic Langevin theory. Note that, the superparamagnetic Co 0.6 Zn 0.4 Fe 2 O 4 ferrite nanoparticle, with excellent performance, can be synthesized at 160°C for a short reaction time (4 h).

Description: We show that multilayer green tapes constituted from sandwiched layers of NiO–zirconia anode and cubic zirconia electrolyte can be sintered below 1000°C in a few seconds under the influence of a DC electric field. The sintering yields a dense electrolyte layer with minor closed porosity, and an anode layer with open porosity, and, most importantly, a multilayer that is largely devoid of defects and delamination.

Description: In this study, magnesium ( Mg ) was doped into the non-calcined amorphous calcium phosphate (ACP) via mechanochemical route, and the as-prepared non-calcined ACP was used to form a novel hydration system. In this novel hydration system, the effects of Mg doping on the hydration reaction and mechanical property of cement were studied. The incorporation of Mg into the hydration product was confirmed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results showed that Mg doping had a significant influence on the nucleation and subsequent growth of apatite crystals. With the Mg doping, the size of hydration crystals was refined, and induced a denser curing body after setting. With the increasing density, the mechanical property of cement was improved effectively. This work explored the inhibiting effect of Mg ions on the nucleation and subsequent growth of apatite under the non-calcined condition.

Description: Tailoring the crystallographic orientation in piezoelectric ceramics is very useful for improving their properties. Orientation in ceramics can be controlled by templated grain growth, hot forging, etc. We have focused on using a strong magnetic field for the crystallographic orientation even in diamagnetic ceramics. In a previous study, although only a one-directional orientation could be controlled by these methods, it was difficult to control the multi-axis orientation in the ceramics. In this study, we demonstrated that alignments of the c -axis and the 〈100〉 axis in Bi 4 Ti 3 O 12 piezoelectric ceramics were controlled by using a strong magnetic field as well as platelet particles. We also estimated the degree of orientation by an electron back scattering diffraction analysis. When the magnetic field was applied to the platelet particles, appropriately 80% of the grains were aligned with the tilt angle made by the c -axis and the vertical direction less than 10° and 73% of grains were oriented with the angle between the 〈100〉 axis and the magnetic field less than 10°.

Description: The disorder in γ–alon is caused by random arrangement of nitrogen atoms and aluminum vacancies. To understand the properties and electronic structure of γ–alon by theoretical methods, the most reasonable structure model is needed. We examined the site preference of nitrogen atoms and aluminum vacancies by first-principles density functional theory (DFT) calculations on Al 24 O 24 N 8 and Al 23 O 27 N 5 . The calculated results for Al 24 O 24 N 8 with the lowest total energy indicated that nitrogen atoms prefer to be far away from each other, rather than in a completely random arrangement. The further investigation on Al 23 O 27 N 5 shows that the aluminum vacancies tend to possess octahedral sites and coordinate only with oxygen atoms. Evaluated by lattice variances ( D a and D θ ) and simulated XRD pattern, the most reasonable structure model of Al 23 O 27 N 5 has little deviation from the experimental results. The calculated bulk modulus of 200.9 GPa in Al 23 O 27 N 5 is slightly lower than the experimental value. The electronic structure reveals that the bonds of Al – N and Al – O have partially covalent and ionic characterization, while the covalent bond strength of Al – N is stronger than that of Al – O . The calculated band gap is 3.99 eV, which is much closer to the experimental 4.56 eV than previous suggestions.

Description: Migration of residual pores in partially sintered 8 mol% yttria-stabilized zirconia under an electric field was investigated. To avoid shrinkage via sintering, Ar -filled bubbles introduced to dense ceramic were also studied. Pores/bubbles were found to migrate against the field, e.g., under 1.9 V at 875°C, a temperature when cation diffusion is supposed to have frozen according to the prevailing consensus. Pore/bubble movement left contorted grains in some samples, but not at lower temperatures and higher fields when they apparently pass through grain boundaries without causing any visible distortion. These results are explained by a surface diffusion model and a temperature-pore-size map that delineates two distinct modes of pore/boundary pinning and breakaway. The implications of these results to solid oxide fuel cells and electrolysis cells are explored.

Description: Macroporous alumina ceramic monolith was fabricated by the novel gelation freezing method with antifreeze protein (AFP). The gelation freezing route with AFP is a simple and efficient way to produce macrocellular ceramics with tailored and uniform pore architecture as well as high porosity.

Description: β-eucryptite ( LiAlSiO 4 ), a member of the family of lithium aluminum silicates, is known to undergo a reversible pressure-induced phase transformation at ~0.8 GPa to ε-eucryptite. This study correlates the results between two techniques, in situ diamond anvil cell–Raman spectroscopy and nanoindentation experiments, to explore how doping (substituting Zn for Li ) influences this pressure-induced phase transformation. Diamond anvil cell tests carried up to 3 GPa hydrostatic stress under Raman spectroscopy were compared with nanoindentation results, which provide a more localized, multiaxial stress state. The results indicate that the magnitude of hysteresis observed (difference between the pressures required for the forward and reverse transformation) is lower for Zn -doped β-eucryptite; however, the onset of the phase transformation is unchanged by doping with Zn . Furthermore, calculations of activation volume from nanoindentation experiments yield similar values (~0.1 nm 3 ) for pure and Zn -doped β-eucryptite, suggesting that the nucleation event that establishes the onset of the phase transformation is the same for both materials.

Description: In this work, both planar and textured, industrial scale (156 mm × 156 mm) single-crystalline silicon ( Si ) solar cells have been fabricated using zinc oxide ( ZnO ) nanorods as antireflection coating (ARC). ZnO nanorods were grown in a few minutes via hydrothermal method within a commercially available microwave oven. Relative improvement in excess of 65% in the reflectivity was observed for both planar and textured Si surfaces. Through ZnO nanorods, effective lifetime (τ eff ) measurements were presented to investigate the surface passivation property of such an ARC layer. ZnO nanorods increased the τ eff from 9 to 71 μs at a carrier injection level of 10 15  cm −3 . Increased carrier lifetime revealed the passivation effect of the ZnO nanorods in addition to their ARC property. 33% and 16% enhancement in the photovoltaic conversion efficiency was obtained in planar and textured single-crystalline solar cells, respectively. Our results reveal the potential of ZnO nanorods as ARC that can be deposited through simple solution-based methods and the method investigated herein can be simply adapted to industrial scale fabrication.

Description: The fabrication of 0.5 mol% Ce:LuAG transparent ceramics starting from synthetic nanosized Ce:LuAG powders was investigated by low temperature vacuum sintering. It was found that high quality optical Ce:LuAG ceramics could be densified successfully by vacuum sintering (〈10 –3 pa) at 1750°C for 10 h. The in-line optical transmittance of as-sintered Ce:LuAG ceramics with thickness of 0.7 mm could reach 73.48% at the wavelength of 550 nm. The microstructure observations revealed that transparent Ce:LuAG ceramics were composed of uniform LuAG grains with average size of 9 μm and HRTEM morphology indicated that no impurity segregation existed at grain boundaries or within Ce:LuAG grains. It was also demonstrated that the annealing treatment (at 1450°C for 20 h in air) could greatly enhance the luminescent intensity of as-sintered Ce:LuAG ceramics under excitation of X-ray radiation (75 kV, 25 mA), which makes it a potential candidate to be applied in radiation detector.

Description: Synthesis of silver-doped zinc oxide ( ZnO : Ag ) nanoparticles through precipitation method has been reported. The synthesis was conducted at room temperature and no subsequent thermal treatment was applied. ZnO nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fourier transmission infrared spectroscopy (FTIR), and ultraviolet-visible (UV–Vis) spectroscopy. Detailed crystallographic investigation was accomplished through Rietveld refinement. The effect of silver content on structural and optical properties of resultant ZnO nanoparticles has been reported. It was found that silver doping results in positional shifts for the XRD peaks and the absorption band edge of ZnO . These were attributed to the substitutional incorporation of Ag + ions into Zn 2+ sites within the ZnO crystal. In addition, higher silver incorporation resulted in smaller size for ZnO nanoparticles. The photocatalytic activity of the ZnO : Ag nanoparticles was also determined by methylene orange (MO) degradation studies and compared to that of undoped ZnO . Improved photocatalytic activity was obtained for ZnO : Ag nanoparticles. It has been shown that an optimum amount of silver dopant is required to obtain maximum photocatalytic activity.

Description: A series of Dy 3+ –Eu 3+ -codoped ZrO 2 nanocrystals with tetragonal and cubic symmetry was synthesized via a wet chemical reaction. When the Eu 3+ -doping content was fixed, the crystal structure could be stabilized from the mixed phase to single cubic phase by simply adjusting the content of Dy 3+ . The cubic ZrO 2 :Dy 3+ –Eu 3+ nanoparticles exhibited spherical and nonagglomerated morphology. The effective phonon energy of cubic ZrO 2 :5%Dy 3+ –5%Eu 3+ was calculated to be 445 cm −1 , which is lower than the previously reported results. Extensive luminescence studies of ZrO 2 :Dy 3+ –Eu 3+ as a function of Dy 3+ content demonstrated that the dopant concentration and its site symmetry play an important role in the emissive properties. Under 352 nm excitation, the increment of Dy 3+ concentration in ZrO 2 :Dy 3+ –Eu 3+ led to an increase in orange (590 nm) and red (610 nm) emissions of Eu 3+ ions, which are attributed to the 5 D 0 → 7 F J ( J  = 1, 2) transitions of Eu 3+ ions. This increment is possibly due to the efficient energy transfer (ET) 4 F 9/2 :Dy 3+ → 5 D 0 :Eu 3+ . The phosphors can generates light from yellow through near white and eventually to warm white by properly tuning the concentration of Dy 3+ ions through the ET and change in site symmetry. These phosphors may be promising as warm-white-/yellow-emitting phosphors.

Description: Eu 3+ -activated borogermanate scintillating glasses with compositions of 25 B 2 O 3 –40 GeO 2 –25 Gd 2 O 3 –(10− x ) La 2 O 3 – x Eu 2 O 3 were prepared by melt-quenching method. Their optical properties were studied by transmittance, photoluminescence, Fourier transform infrared (FTIR), Raman and X-ray excited luminescence (XEL) spectra in detail. The results suggest that the role of Gd 2 O 3 is of significance for designing dense glass. Furthermore, energy-transfer efficiency from Gd 3+ to Eu 3+ ions can be near 100% when the content of Eu 2 O 3 exceeds x  =   4, the corresponding critical distance for Gd 3+ – Eu 3+ ion pairs is estimated to be 4.57 Å. The strongest emission intensities of Eu 3+ ions under both 276 and 394 nm excitation are simultaneously at the content of 8 mol% Eu 2 O 3 . The degree of Eu – O covalency and the local environment of Eu 3+ ions are evaluated by the value of Ω t parameters from Judd–Ofelt analysis. The calculated results imply that the covalency of Eu – O bond increases with the increasing concentration of Eu 3+ ions in the investigated borogermanate glass. As a potential scintillating application, the strongest XEL intensity under X-ray excitation is found to be in the case of 6 mol% Eu 2 O 3 , which is slightly different from the photoluminescence results. The possible reason may be attributed to the discrepancy of the excitation mechanism between the ultraviolet and X-ray energy.

Description: Using synchrotron X-ray diffraction and diamond anvil cells we performed in situ high-pressure studies of mullite-type phases of general formula Al 4+2 x Si 2−2 x O 10− x and differing in the amount of oxygen vacancies: 2:1-mullite ( x  =   0.4), 3:2-mullite ( x  =   0.25), and sillimanite ( x  =   0). The structural stability of 2:1-mullite, 3:2-mullite, and sillimanite was investigated up to 40.8, 27.3, and 44.6 GPa, respectively, in quasi-hydrostatic conditions, at ambient temperature. This is the first report of a static high-pressure investigation of Al 2 O 3 – SiO 2 mullites. It was found that oxygen vacancies play a significant role in the compression mechanisms of the mullites by decreasing the mechanical stability of the phases with the number of vacancies. Elevated pressure leads to an irreversible amorphization above ~20 GPa for 2:1-mullite and above 22 GPa for 3:2-mullite. In sillimanite, only a partial amorphization is observed above 30 GPa. Based on Rietveld structural refinements of high-pressure X-ray diffraction patterns, the pressure-driven evolution of unit cell parameters is presented. The experimental bulk moduli obtained are as follows: K 0 = 162(7) GPa with K 0 ′ = 2.2(6) for 2:1-mullite, K 0 = 173(7) GPa with K 0 ′ = 2.3(2) for 3:2-mullite, K 0 = 167(7) GPa with K 0 ′ = 2.1(4) for sillimanite.

Description: Third-generation SiC fibers [High Nicalon S (HNS) and Tyranno SA3 ( Ty –SA3)] were studied by X-ray diffraction and transmission electron microscopy (TEM) after heat treatments in neutral atmosphere up to 1900°C. The microstructural changes in both materials were determined using a modified Hall–Williamson method introducing an anisotropy parameter taking into account the high density of planar defects. HNS fibers exhibit significant modifications in the coherent diffraction domains (CDD) size, which drastically increases from 24 to 70 nm in the range 1600°C–1900°C. TEM observations support these results. The residual microstrain values decrease from 0.0015 to 0.0005 between 1750°C and 1850°C. Similarly, the anisotropy parameter significantly decreases in the same temperature range. Concerning the Ty–SA3 fibers, no evolution in terms of CDD size and residual microstrain was observed. However, the anisotropy parameter decreases at 1800°C. TEM observations did not show noticeable grain growth. The grain size was found to be larger than the CDD and the planar defects density to decrease at high temperature. In both types of fibers, the CDD sizes are similar for the highest temperature heat treatments.

Description: This study investigated the effects of the addition of Nb 2 O 5 and sintering temperature on the properties of Bi 2 Mo 2 O 9 ceramics. The ceramics were sintered in air at temperatures ranging from 620°C to 680°C. The addition of small amounts of Nb 2 O 5 as a dopant significantly affected the crystalline phase and the microwave dielectric properties of the Bi 2 Mo 2 O 9 ceramics. The secondary phase, γ- Bi 2 MoO 6 , was observed when Nb 2 O 5 was added. However, unlike the Bi 2 Mo 2 O 9 ceramic without Nb 2 O 5 sintered above 645°C, the ceramics with 3 mol% Nb 2 O 5 contained no γ- Bi 2 MoO 6 when sintered at 660°C. The Q  ×  f value and τ f of the Bi 2 Mo 2 O 9 ceramics were improved by Nb 2 O 5 doping. The Bi 2 Mo 2 O 9 ceramics doped with 2 mol% Nb 2 O 5 exhibited the best microwave dielectric properties, with a permittivity of 36.5, a Q  ×  f value ( f  = resonant frequency, Q  = 1/dielectric loss at f ) of 14100 GHz and τ f of +5.5 ppm/°C after sintering at 620°C.

Description: We, herein, present comparative investigations on the Na 0.5 Bi 0.5 Cu 3 Ti 4 O 12 ceramic samples with and without 10 mol% excess of Na / Bi . The samples were prepared by the standard solid-state reaction technique. The dielectric properties of the sample were investigated in the temperature (93–320 K) and frequency (20 Hz–10 MHz) windows. Three thermally activated dielectric relaxations observed in Na 0.5 Bi 0.5 Cu 3 Ti 4 O 12 with the activation energies of 0.104, 0.267, and 0.365 eV for the low-, middle-, and high-temperature dielectric relaxations, respectively. Only the low-temperature relaxation was observed in both Na and Bi excessive samples. X-ray photoemission spectroscopy results revealed the mixed-valent structures of Cu + / Cu 2+ and Ti 3+ / Ti 4+ in Na 0.5 Bi 0.5 Cu 3 Ti 4 O 12 sample, but only Ti 3+ / Ti 4+ in Na and Bi excessive samples. Our results showed that the dielectric properties of the investigated samples are strongly linked with these mixed-valent structures. The high- and low-temperature relaxations were attributed to be a polaron-type relaxation due to localized carriers hopping between Cu + / Cu 2+ and Ti 3+ / Ti 4+ , respectively. The middle-temperature relaxation is suggested to be a dipole-type relaxation caused by the defect complex of bismuth and oxygen vacancies.

Description: Contact damage in the form of localized cracking and inelastic deformation is of concern in the utilization of ceramics and is often studied using hard indenters; an approach that has spawned the field of indentation mechanics. This approach was taken in the current work to study the penetration resistance at low strain rates of four candidate ceramic armor materials: MgAl 2 O 4 with two grain sizes, AlON and AlN . Spherical indentation was chosen as this allows the elastic–plastic behavior to be studied and the indentation stress–strain curves to be determined. To further quantify these data, the elastic and plastic indentation work contributions were measured. On empirical grounds, it was postulated that the area under the indentation stress–strain curves, termed the indentation strain energy density, was related to the total indentation work could be used to quantify the penetration resistance. As a test of this hypothesis, it was shown that the total indentation work correlated with the strain energy density and acted over a volume similar to that of the stress field. A simple figure of merit, derived from the indentation strain energy density, was suggested as a means to quantify the penetration resistance of materials at low strain rates and to identify the material parameters that control this process.

Description: This work focused on the synthesis of high-activity strontium titanate ( SrTiO 3 ) photocatalysts through an environmentally friendly process. A high energy-efficient microwave-assisted hydrothermal method was employed to prepare Fe -loaded SrTiO 3 that consisted of small particles around 50 nm in diameter. To achieve the effective assistance of long-lasting fluorescence, the obtained Fe -loaded SrTiO 3 samples were coupled with CaAl 2 O 4 :( Eu , Nd ). The photocatalytic activities were evaluated by the photo-decomposition of NO . Fe loaded SrTiO 3 showed high photocatalytic activities not only under visible light irradiation but also in the dark with fluorescence assistance.

Description: Sm 3+ -doped glass 13 SrO –2 Bi 2 O 3 –5 K 2 O –80 B 2 O 3 was fabricated by the conventional melt-quenching technique. The glass-ceramics were obtained by heating the as-prepared glasses in air atmosphere at selected temperatures 550°C, 600°C, 615°C, and 650°C, respectively. The luminescence spectra of both Sm 3+ and Sm 2+ were detected in the ceramic heated at 650°C where crystalline phase is formed. The as-prepared glass and the ceramics heated at 550°C, 600°C, and 615°C show only the emission due to Sm 3+ . In the sample heated at 650°C in air atmosphere, however, part of Sm 3+ ions was converted to Sm 2+ , giving rise to sharp emission lines which are characteristic of Sm 2+ in crystalline state. It is suggested that Sm 2+ ions are located at Sr 2+ site in the ceramic while Sm 3+ ions are located at Bi 3+ sites. The Sm 2+ -doped glass-ceramic has a high optical stability because the fluorescence intensity decreases by only about 8% of its initial value upon excitation at 488 nm Ar + laser.

Description: Improvement of electrocaloric effect was investigated in the lead-free undoped and Mn -doped Ba 0.65 Sr 0.35 TiO 3 ceramics prepared by spark plasma sintering process. Owing to the merit of spark plasma sintering process, a fully dense undoped and Mn -doped Ba 0.65 Sr 0.35 TiO 3 ceramics with fine grain sizes could be obtained. The electrocaloric (EC) effect can be significantly enhanced from 0.83 K for conventional sintered Ba 0.65 Sr 0.35 TiO 3 to 3.08 K for spark plasma-sintered Mn -doped Ba 0.65 Sr 0.35 TiO 3 ceramics since the dielectric strength was dramatically increased. This work indicated an effective way to achieve the significantly enhanced EC effect in a lead-free system at room temperature.

Description: The model developed by Makishima and Mackenzie (M–M) may yield reasonable estimates for the E-modulus of a range of glasses. In the M–M model the bonding enthalpy and packing densities present in the compounds that form the glass are taken as input for the calculation. This study shows that a more accurate estimate can be obtained by incorporating in the model structural information from MAS-NMR data. Specifically, we have determined by means of the impulse excitation technique (IET) the E-modulus for ionomer glasses with composition 4.5 SiO 2 –3 Al 2 O 3 –1.5 P 2 O 5 –3MO–2MF 2 , where M denotes the alkaline earth metal (M = Mg , Ca , Sr , or Ba ). The MAS-NMR structural analysis shows that substitution of calcium by barium or strontium results in a disrupted network, whereas magnesium leads to a more packed network. In this study we will show how a higher coordination state of the aluminum as determined by 27 Al MAS-NMR can be taken into account in the model. This leads to rather small corrections of the estimates for these particular glasses. In contrast, the 19 F MAS-NMR study shows the presence of Al – F – M (n) or Al – F and Si – F – M (n) types of environment in the glass network. Al – F and Si – F bonds are not accounted for in the E-modulus estimate by the M–M model. We will show how by incorporating the new bonding of F with Al and Si a significantly improved estimate of the E-modulus is obtained compared with the original model.

Description: Thin films of nanocrystalline ceria deposited onto a silicon substrate have been irradiated with 3 MeV Au + ions to a total dose of 34 displacements per atom to examine the film/substrate interfacial response upon displacement damage. Under irradiation, a band of contrast is observed to form that grows under further irradiation. Scanning and high-resolution transmission electron microscopy imaging and analysis suggest that this band of contrast is a cerium silicate phase with an approximate Ce : Si : O composition ratio of 1:1:3 in an amorphous nature. The slightly nonstoichiometric composition arises due to the loss of mobile oxygen within the cerium silicate phase under the current irradiation condition. This nonequilibrium phase is formed as a direct result of ion-beam-induced chemical mixing caused by ballistic collisions between the incoming ion and the lattice atoms. This may hold promise in ion beam engineering of cerium silicates for microelectronic applications e.g., the fabrication of blue LEDs.

Description: Pure yttrium aluminum garnet (YAG) phosphor doped with Eu 2+ has been successfully synthesized by a facile sol–gel method. The use of hydrogen iodide aimed to get Eu 2+ ions, confirmed by X-ray absorption near-edge structure (XANES) analysis. Nearly spherical and well dispersed particles were synthesized. The produced YAG:Eu 2+ phosphor powder had a broad emission band in the range of 400–600 nm with a peak at 480 nm, attributed to the allowed 4 f 7 –4 f 6 5 d 1 transition of electrons in Eu 2+ ions. The proposed method could also be expanded to prepare many other Eu 2+ -doped phosphors with a solution method.

Description: A new sulfated chitosan superplasticizer (SCS) was synthesized by sulfation chitosan. The chemical structure and molecular weight of SCS were characterized by FTIR and gel permeation chromatography (GPC). The application performances of SCS in cement paste and concrete were investigated in the views of fluidity, slump, setting time, porosity as well as compressive strength. The results indicated that the SCS has better applied performance compared with polycarboxylate superplasticizer (PCs). A notable feature is that SCS has better maintenance for cement paste fluidity and concrete slump. The action mechanism behind this behavior was further revealed by zeta-potential and adsorption amount. Meanwhile, SCS comes from renewable source and has biodegradability. This research work provides not only a new superplasticizer but also a method for preparing superplasticizer from the renewable biopolymer.

Description: We show that water-based porosimetry (WBP), a facile, simple, and nondestructive porosimetry technique, accurately evaluates both the pore size distribution and throat size distribution of sacrificially templated macroporous alumina. The pore size distribution and throat size distribution derived from the WBP evaluation in uptake (imbibition) and release (drainage) mode, respectively, were corroborated by mercury porosimetry and X-ray micro-computed tomography (μ-CT). In contrast with mercury porosimetry, the WBP also provided information on the presence of “dead-end pores” in the macroporous alumina.

Description: We reported the dielectric properties of Pb ( Mg 1/3 Nb 2/3 ) O 3 – PbTiO 3 single crystal in the temperature range of 300–1073 K and the frequency range of 100 Hz–10 MHz. Our results showed the coexistence of both true- and pseudo-relaxor behaviors in the crystal. The true relaxor behavior related to the paraelectric-ferroelectric phase transition occurs at~423 K. The pseudo-relaxor behavior appearing at~773 K was found to be related to oxygen vacancies. Further investigation reveals that the pseudo-relaxor behavior has fine structure: it contains two oxygen-vacancy-related relaxation processes. The low-temperature relaxation process is a dipolar relaxation created by the hopping motions of the oxygen vacancies, and the high-temperature relaxation process is a Maxwell-Wagner relaxation caused by the sample/electrode contacts.

Description: Millimeter-sized hydroxyapatite (HA) single crystals were synthesized from chlorapatite (ClAp) crystals via the ionic exchange of Cl − for OH − at high temperature. X-ray diffraction, Fourier-transform infrared spectroscopy, and chloride content measurements were used to follow the progress of this conversion, and to assess the effect of the experimental conditions (temperature, time, and atmosphere). Cl − → OH − exchange took place homogeneously and was enhanced by firing in wet air. After firing at 1425°C for 2 h 92% of the Cl − ions were exchanged by OH − while maintaining crystal integrity. Temperatures above 1450°C damaged the surface of the crystals, destroying the hexagonal habit at 1500°C. The composition of these apatite crystals was close to bone mineral content. Their nanoindentation hardness (8.7 ± 1.0 GPa) and elastic nanoindentation modulus (120 ± 10 GPa) were similar to those of the starting ClAp (6.6 ± 1.5 GPa, and 110 ± 15 GPa, respectively). However, their average flexural strength was ~25% lower due to the formation of defects during the thermal treatments.

Description: This work examines the synthesis and characterization of crack-free, β- Bi 2 O 3 thin films prepared on Pt / TiO 2 / SiO 2 / Si or corundum substrates using the sol-gel method. We observed that the Bi -based precursor has a pronounced influence on the β- Bi 2 O 3 phase formation. Well-crystallized, single β- Bi 2 O 3 thin films were obtained from Bi -2ethylhexanoate at a temperature of 400°C. In contrast, thin films deposited from Bi -nitrate and Bi -acetate resulted in non-single Bi 2 O 3 phase formation. TEOS was used for the stabilization of the β- Bi 2 O 3 phase. The phase composition of the thin films was characterized by means of X-ray diffraction (XRD), whereas the morphology and thickness of the thin films were studied using scanning electron microscopy (SEM). The β- Bi 2 O 3 films' dielectric properties were characterized utilizing microwave-frequency measurement techniques: (1) the split-post dielectric resonator method (15 GHz) and (2) the planar capacitor configuration (1–5 GHz). The dielectric constant and dielectric loss measured at 15 GHz were 257 and 7.5 × 10 −3 , respectively.

Description: Novel low temperature firing microwave dielectric ceramic LiCa 3 MgV 3 O 12 (LCMV) with garnet structure was fabricated by the conventional solid-state reaction method. The phase purity, microstructure, and microwave dielectric properties were investigated. The densification temperature for the LCMV ceramic is 900°C. LCMV ceramic possessed ε r = 10.5, Q u  ×  f  =   74 700 GHz, and τ f = −61 ppm/°C. Furthermore, 0.90 LiCa 3 MgV 3 O 12 –0.10 CaTiO 3 ceramic sintered at 925°C for 4 h exhibited good properties of ε r = 12.4, Q u  ×  f  = 57 600 GHz, and τ f = 2.7 ppm/°C. The LCMV ceramic could be compatible with Ag electrode, which makes it a promising ceramic for LTCC technology application.

Description: The microstructures of the Bi 0.4 Ca 0.6 MnO 3 (BCMO) and La 0.67 Ca 0.33 MnO 3 (LCMO) epitaxial films are investigated by transmission electron microscopy in detail. BCMO epitaxial films (~ 10 and ~ 40 nm) exhibit an island growth mode whereas the LCMO films (~ 6 and ~ 30 nm) follow a layer by layer growth mode. Combined with the critical thickness models for the expected onset of the misfit dislocations in epitaxial films, an atomic collapse model is introduced to explain their mechanism of formation in manganite films. At the beginning of deposition, the strain caused by the lattice mismatch between the epitaxial film and substrate can be accommodated by elastic deformation. With the increase of film thickness, the strain becomes larger and larger. When the film thickness reaches the critical thickness, the strain can only be relaxed by the formation of misfit dislocations. Meanwhile, the atomic configuration of the epitaxial film will reorganize and some atoms begin to collapse, thus an island morphology will be formed. Once the collapse morphology is formed, maintenance of this wave-like morphology depends on atomic diffusion length of the deposited atoms. If the diffusion length of the deposited atoms is long, the island morphology will not be maintained. If the diffusion length of the deposited atoms is short, the island morphology will keep until the epitaxial film is thick enough. The results could shed light on the growth modes for other perovskite epitaxial films.

Description: Sharp leading edge (LE) samples of UHTC (20 vol% SiC – HfB 2 ) and SiC were exposed to simulated hypersonic flight conditions using a direct-connect scramjet rig and their thermal and oxidation responses measured. The measured back-wall temperatures and scale thicknesses were significantly smaller than might be expected from stagnation temperatures at the LE. Furthermore, the scale that formed around the LE was more uniform than expected from the steep drop in cold wall heat flux with distance from the tip. These results were interpreted and rationalized using physics-based models. An aerothermal model in combination with an oxidation model accounted for the observed scale thicknesses at the tip and their slight variation with distance. The scale thicknesses were similar to values reported for exposures in furnaces at temperatures calculated for the tip, but less than those reported in arc jet tests. The formation of hafnon (HfSiO 4 ) and the absence of external glassy layer and of silica in the outer portions of the oxide region are unique to scramjet tested samples, presumably due to the high fluid flow (high shear and evaporation) rates.

Description: Amorphous BaTi 4 O 9 (BT4) films for use as capacitors embedded in PCB substrates were grown on Cu electrodes at low temperatures (≤ 200°C). The dielectric constant ( k ) of the amorphous BT4 film grown at room temperature (RT) was 38, and its dissipation factor was 3.2% at 100 kHz. A similar k value was obtained at radio-frequency ranges, with a quality factor of 143 at 1.0 GHz. The films showed a capacitance density of 200 nF/cm 2 , a temperature coefficient of capacitance of 296 ppm/°C at 75 kHz, and a breakdown voltage of 42.5 V. This film therefore satisfies the requirements of the International Technology Roadmap for Semiconductors for 2016 for capacitors grown on organic substrates. In addition, the leakage current mechanism of the amorphous BT4 films was found to be Schottky emission, and the Schottky barrier height was calculated as 2.26 eV.

Description: This work reports the oxidation and crack healing behavior of a fine-grained (~2 μm) Cr 2 AlC MAX phase ceramic. The oxidation behavior was investigated in the temperature range 900°C–1200°C for times up to 100 h. The material showed a good oxidation resistance, owing to the formation of a dense and thin α- Al 2 O 3 layer. The microstructure, composition and thickness of the oxide scale were characterized. Its oxidative crack healing behavior as a function of temperature, healing time, and initial crack size was studied systematically. The material showed excellent healing behavior. The main crack healing mechanism is the filling of the crack by oxides well adhering to the crack faces. The crack geometry before and after healing was characterized by X-ray tomography. Three-point bend tests showed the dependence of strength recovery at 1100°C as a function of initial crack length and healing time.

Description: Diffusion properties of Tm 3+ in congruent LiNbO 3 crystal have been investigated, together with other two related issues, i.e., Tm 3+ -doping contribution to refractive index of LiNbO 3 substrate and Li out-diffusion. Four X -cut and four Z -cut congruent LiNbO 3 substrates locally coated with 15–31 nm-thick Tm-metal films were annealed in surrounding air under different temperatures of 1030°C–1130°C for different durations of 20–70 h. After anneal, refractive index at Tm 3+ -doped and Tm 3+ -free parts of crystal surface was measured at the wavelengths of 1311 and 1553 nm and surface Li 2 O contents were evaluated from measured refractive index. The results show that Tm 3+ doping has a weak effect on substrate index and a small contribution to index increment in waveguide layer in comparison with Ti 4+ - or Zn 2+ doping. The Li 2 O content at the Tm 3+ -doped surface equals that at the Tm 3+ -free surface. The Li out-diffusion depends mainly on the diffusion temperature. Below 1100°C, the Li out-diffusion is not measurable. At 1130°C, a 30-h diffusion procedure may cause 0.2–0.3 mol% slight loss of Li 2 O content. Secondary ion mass spectrometry was used to study the Tm 3+ diffusion properties. The results show that the diffused Tm 3+ ions in all samples follow a complementary error function profile. From measured Tm 3+ profiles, characteristic diffusion parameters such as diffusivity, diffusion constant, activation energy, solubility, solubility constant, and heat of solution were obtained and discussed in comparison with the case of Er 3+ diffusion. In comparison with Er 3+ diffusion, the Tm 3+ diffusion shows similar anisotropy and temperature dependence of solubility. In the aspect of diffusivity, under lower temperature the Tm 3+ has a lower diffusivity than the Er 3+ , and their diffusivity difference reduces with the increased temperature and becomes null at 1130°C.

Description: Phase-pure powders of stoichiometric BiFeO 3 have been prepared by mechanosynthesis. Ceramics sintered by either conventional heating in air or spark plasma sintering (SPS) followed by oxidative anneal in air are highly insulating at room temperature with resistivity, extrapolated from the Arrhenius plots, of ~10 16  Ωcm and activation energy 1.15(2) eV, comparable with those of a good-quality BiFeO 3 single crystal. By contrast, the as-prepared SPS sample without the postsinter anneal shows lower resistivity, e.g., ~10 10  Ωcm at 25°C and activation energy 0.67(3) eV, indicating some reduction in the sample by the SPS process. The reason for the high conductivity reported for some ceramic samples in the literature remains unclear at present.

Description: The BT/NZFO composite ceramics derived by sol–gel in situ process were successfully prepared. The phase composition, morphology, and microstructure of the composite ceramics were determined and observed by X-ray diffractometer (XRD), SEM, and EDS. Results showed that the Ni–Zn ferrite (NZFO) phase started to grow initially and then the BaTiO 3 (BTO) phase grew among the interfaces of NZFO particles at high ferrite content. The observation of microstructure showed that the NZFO phase in large grain size is enwrapped by the BTO phase in small grain size, and the constituent phases existed in the form of solid solutions doped with Fe and Ti , respectively. The densification and microstructure depended on the volume fraction of ferrite ( f NZFO ). The appropriate sintering temperature was 1280°C–1300°C at which stable phase structure could be obtained for the BTO/NZFO composite. The maximum permittivity could achieve 86 000, and the initial permeability was as high as 162 when the ceramics was loaded with 95% ferrite and sintered at 1300°C for 12 h. The BT/NZFO composite ceramics exhibited impressive dielectric and magnetic properties, making it a potential candidate for wide applications in the integration of electronic devices.

Description: A catalytic combustion-type gas sensor using a positive temperature coefficient (PTC) thermistor, which shows a sharp resistance change around Curie temperature, was developed for the detection of hydrogen. La -doped BaTiO 3 ( Ba 0.998   La 0.002   TiO 3 ) was prepared through a solid-state method and an oxalic acid method. La -doped BaTiO 3 obtained by the oxalic acid method showed improved PTC properties, due to the formation of fine particles, as compared to that prepared with the solid-state method. The resulting sensor device showed a fairly high H 2 sensitivity in the range of 100–1000 ppm. In addition, the H 2 sensitivity and response speed were improved by coating a Pt / SiO 2 catalyst on the sensor device because the catalytic combustion efficiency of H 2 was improved by the catalyst coating.

Description: Single-crystalline potassium tungsten bronze nanosheets were prepared by reducing potassium tungsten oxide nanosheets grown on a W foil. The nanosheets showed no evident shape change before and after reduction. Morphology, structure, and composition analyses revealed that a phase transformation from orthorhombic potassium tungsten oxide to hexagonal potassium tungsten bronze occurred. Better field emission with lower turn-on field was measured from potassium tungsten bronze nanosheet film. The effects of reduction treatment on field emission performance are discussed.

Description: The 10 mol% ZnO –2 mol% B 2 O 3 –8 mol% P 2 O 5 –80 mol% TeO 2 (ZBPT) glass was prepared by quenching as well as slowly cooling the melt. The ZBPT glass prepared by both methods show similar microwave dielectric properties. ZBPT glass has an ε r of 22.5 (at 7 GHz), Q u  ×  f of 1500 GHz, and τ f of −100 ppm/°C. The ceramic-glass composites of Sr 2 Zn TeO 6 (SZT) and ZBPT is prepared through two convenient methods: ( a ) conventional way of co-firing the ceramic with ZBPT glass powder and ( b ) a nonconventional facile route by co-firing the ceramic with precursor oxide mixture of ZBPT glass at 950°C. In the former route, SZT + 5 wt% ZBPT composite sintered at 950°C showed moderately good microwave dielectric properties (ε r  = 13.4, Q u  ×  f  = 4500 GHz and τ f  = −52 ppm/°C). Although the SZT + 5 wt% ZBPT composite prepared through the nonconventional method also showed similar microwave dielectric properties (ε r  = 13.8, Q u  ×  f  = 5300 GHz and τ f  = −50 ppm/°C), the synthesis procedure is much simplified in the latter case. The composites are found to be chemically compatible with Ag. The composite containing 5 wt% ZBPT prepared through conventional and nonconventional ways shows linear coefficients of thermal expansion of 7.0 ppm/°C and 7.1 ppm/°C, respectively. Both the composites have a room-temperature thermal conductivity of 2.1 Wm −1  K −1 .

Description: The early age ambient temperature hydration of a hybrid cement formulation containing very high volumes of coal fly ash (~80% by dry mass) and activated by Na 2 SO 4 is presented. The Na 2 SO 4 salt acts as a safe and convenient in situ source of alkali to activate fly ash glassy phases without undesirable effects on cement clinker hydration. Comparison to a reference paste with gypsum instead of sodium sulfate revealed that Na 2 SO 4 reduced setting times, shortened the induction period, and increased early alite hydration and compressive strength development, but also restricted ettringite formation. When replacing the active fly ash component for milled sand of a similar particle size, the Na 2 SO 4 -activated pastes set even quicker, no ettringite was observed, and early strengths were considerably reduced. Possible reaction mechanisms in the hybrid pastes are discussed.

Description: Based on a novel approach that takes into account the coacervation of calcium and poly(acrylic acid) (PAA), we were able to biomimetically produce molded micropatterned parts from amorphous calcium carbonate (ACC) particles. We studied the time- and concentration-dependent growth of Ca 2+ /PAA coacervate droplets using dynamic light scattering (DLS) and turbidity measurements. Applying these results for the generation of high amounts of unstable ACC particles, we were able to produce slurries that could be molded into micropatterned casts. The obtained slurries contained both micrometer sized ACC particles and smaller nano-sized particles. When both types of particles were used for molding, materials with a high surface roughness could be produced, while the micropatterns of the molds could not be reproduced properly. However, by removing the bigger particles from the slurry using only the smaller, unstable, ACC particles, good reproduction of the micropatterns could be achieved, yielding smooth surfaces with a high surface area. The processing route represents a versatile platform for the bottom-up preparation of micropatterned ceramics on the basis of calcium carbonate.

Description: The Ca ( Zr 1− x Ti x ) O 3 (CZT) solid solution system is a linear dielectric that is of interest for high-temperature power capacitor applications. This dielectric was synthesized by conventional solid-state processes and prototyped into single-layer CZT capacitors, which were fabricated with interdigitated electrodes cofired between dielectric layers ~10-μm thick. The dielectric properties of these capacitors were extensively investigated as a function of Zr / Ti ratio on the CaZrO 3 side of the solid solution. The electrostatic energy density and breakdown strength of the CZT capacitors were investigated by measuring polarization–electric field curves as a function of temperature from room temperature to 250°C. The Ca ( Zr 0.80 Ti 0.20 ) O 3 capacitors show high electrostatic energy density of 4 J/cm 3 at 250°C. Highly accelerated life testing (HALT) was also performed on these dielectrics, and we quantified the thermal stimulated depolarization current (TSDC) to access the major point defects in the CZT system.

Description: Knowledge of thermal behavior of electrolyte is important for fuel cell fabrication. In this study, using high-temperature X-ray diffraction analysis (HT-XRD) and thermo-mechanical analysis (TMA), a systematic investigation of lattice constants was performed on Y-doped BaZrO 3 , which is a promising candidate for electrolyte in protonic ceramic fuel cells. The results revealed that a chemical expansion was observed between 300°C and 450°C during the heating process in HT-XRD, and was attributed to the dehydration of BZY. Furthermore, it was found that the lattice constants of the samples doped with Y, Sm, Eu, and Dy were larger for the ones finally heat-treated at 1600°C for sintering than those heat-treated at 1300°C for synthesizing. The similar behavior was not observed in Sc-doped samples.

Description: We present an interesting processing route for obtaining alumina/mullite-based ceramics with controlled porosity and airflow resistance leading to promising microstructures for application as sound absorbers. The use of ceramic materials aims for potential applications where high temperatures or corrosive atmospheres are predominant, e.g., in combustion chambers of gas turbines. For the production of the porous ceramics we combined freeze gelation and sacrificial templating processes to produce near-net-shaped parts with low shrinkage (〈3%) based on environmental-friendly and low cost conditions. The obtained microstructure presents a bimodal pore size distribution, with small pores derived from the freeze gelation process (~30 μm) connecting large pores (2–5 mm diameter) originated from the expanded polystyrene template particles. These connections, called “windows” in this study, show a significant impact on the sound absorption properties, allowing the pressure diffusion effect to take place, resulting in a significant improvement of the sound absorption coefficient. By varying the template particle content and the slurry solid content, it is possible to control the sound absorption behavior at different frequencies of the open-celled ceramics. These ceramics feature a high open porosity, from 77% to 82%, combined with sufficient compressive strength ranging from 0.27 to 0.68 MPa and sound absorption coefficients of 0.30–0.99, representing a highly promising combination of properties for noise control and reduction at corrosive environments and high temperatures.

Description: Strontium niobate (Sr:Nb  =  1:1) thin films were prepared via chemical solution deposition on (001)-oriented SrTiO 3 , (001) p -oriented LaAlO 3 , (0001)-oriented sapphire, and polycrystalline alumina substrates. Crystallization in oxygen at 1000°C yielded Sr 2 Nb 2 O 7 films on all substrates with strong (010) orientation. Films on LaAlO 3 and SrTiO 3 single-crystal substrates possessed a small amount of preferred in-plane orientation, whereas films prepared on sapphire and polycrystalline alumina substrates were fiber textured. Films crystallized at 900°C in a low oxygen atmosphere (~10 − 21  atm p O 2 ) formed a randomly oriented polycrystalline perovskite, SrNbO 3−δ on all substrates. A similar set of films crystallized at 900°C at a slightly higher oxygen partial pressure (~10 −15  atm p O 2 ) was comprised of Sr 2 Nb 2 O 7 and SrNbO 3−δ phases, exposing the dependence of phase formation on oxygen partial pressure. When subjected to a high-temperature anneal in oxygen, the SrNbO 3−δ phase is shown to transform into Sr 2 Nb 2 O 7 , however, Sr 2 Nb 2 O 7 did not significantly reverse transform into SrNbO 3−δ after annealing in low oxygen partial pressure atmospheres.

Description: The color-tunable up-conversion (UC) emission and infrared photoluminescence and dielectric relaxation of Er 3+ / Yb 3+ co-doped Bi 2 Ti 2 O 7 pyrochlore thin films prepared by a chemical solution deposition method have been investigated. The pyrochlore phase structure of Bi 2 Ti 2 O 7 can be stabilized by Er 3+ / Yb 3+ co-doping. Intense color-tunable UC emission and infrared photoluminescence can be detected on the thin films excited by a 980 nm diode laser. Two UC emission bands centered at 548 and 660 nm in the spectra can be assigned to 2 H 11/2 , 4 S 3/2 → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 transitions of Er 3+ ions, respectively. A Stokes infrared emission centered at 1530 nm is due to 4 I 13/2 → 4 I 15/2 transition of Er 3+ ions. The dependence of UC emission intensity on pumping power indicates that the UC emission of the thin films is a two-photon process. The thin films also exhibit a relatively high dielectric constant and a low dissipation factor as well as a good bias voltage stability. Temperature- and frequency-dependent dielectric relaxation has been confirmed. This study suggests that Er 3+ / Yb 3+ co-doped Bi 2 Ti 2 O 7 thin films can be applied to new multifunctional photoluminescence dielectric thin-film devices.

Description: The substitution in ( Ba 0.70 Sr 0.30 ) TiO 3 thin films by the rare-earth element dysprosium prepared at 1000°C by chemical solution deposition on nickel foils was investigated. The relatively large thermal budget applied (via annealing temperature) is shown to enhance the solubility of the Dy 3+ doping ion into the crystal lattice of the perovskite films. Preference for B-site occupancy of this amphoteric cation was further promoted by the addition of BaO excess (1 mol%), which results in slightly larger grains in the films as observed by scanning electron microscopy. Despite this Ba -rich composition, the presence of secondary phases in the thin films was not detected by X-ray diffraction. Transmission electron microscopy revealed no evidence for local segregation of Dy at grain boundaries, neither the formation of NiO at the interface between the film and the metal foil was observed. The substitution of Ti 4+ by Dy 3+ leads to the formation of strong electron acceptors in the system, which balance the number of ionized oxygen vacancies arisen from the reductive crystallization atmosphere used during processing. As a consequence, the dielectric loss (tan σ) and leakage conduction measured in the resulting thin-film capacitors were significantly reduced with respect to nominally undoped samples. The improvement of this capacitor feature, combined with the relatively high permittivities obtained in the films (490–530), shows the effectiveness of dysprosium doping within a thin-film fabrication method for potential application into the multilayer ceramic capacitor technology.

Description: Amorphous bioactive glasses such as 45S5 have been successfully used in bone-filling therapy in non-load bearing biomedical applications for decades. In this study, we challenge the predilection to amorphous over crystalline ceramics by investigating the effect of synthesis route on surface texture, in vitro dissolution, and mineral formation on powders produced by sol–gel and glass melt-casting methods. Many reports have indicated bulk crystalline bioactive glass-ceramics to be less bioactive than their amorphous counterparts as measured by the onset time for mineral formation. Bioactive glass 45S5 was synthesized using the sol–gel method followed by heat treatment to produce a semi-crystalline structure and was compared against commercially available amorphous melt-cast 45S5 powder. Gel-derived samples were stabilized at 700°C making more than 80% of the structure crystalline. Dissolution of 45S5 glass-ceramic in powder form(particle diameter 12 μm) was studied by in vitro immersion in simulated body fluid solution for various periods of time. The immersed powders were then analyzed through X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), Differential scanning calorimetry (DSC), and thermogravimetric analysis (DSC/TGA), and Fourier transform infrared spectroscopy (FTIR) to determine the onset time for surface mineralization, and were compared with the melt-cast powder as a control. The rates of dissolution and onset time for mineral formation were similar for the gel-derived powder as compared with the melt-cast control; it is proposed that the higher surface area of the sol–gel powder overcame the penalty usually associated with lower dissolution rates of crystalline materials, implicating surface texture as a much more important determinant of dissolution and mineralization behavior than mere crystallinity.

Description: In this work the gas evolution behavior and the fining ability of the alkali-free alkaline earth aluminoborosilicate glass batches doped with As 2 O 5 or SnO 2 were examined, and the redox behavior of As and Sn ion in the corresponding fined melts was investigated by square wave voltammetry. The evolved gas analysis showed a distinct difference at begin temperature of O 2 emission and in evolved O 2 volume between glass batches doped with As 2 O 5 and SnO 2 . One peak due to reduction of As 5+ to As 3+ or Sn 4+ to Sn 2+ was shown in the voltammograms. Glass batch doped with SnO 2 showed better fining in the first fining zone, but batch doped with As 2 O 5 is more excellent in the overall fining inclusive of the second fining. This difference in fining behavior was discussed by combination of O 2 evolution from batches and redox ratio in melts. Finally, it was suggested that the earlier oxidation of As ion in the second fining zone contributed to the excellent fining of melts.