ALBERT

Description: In this work, we report on the temperature-dependent crystal structures of the isostructural, layered hexagonal phases Ti 2 AlN and Cr 2 GeC determined by Rietveld analysis of high temperature neutron powder diffraction data of fully dense, polycrystalline, bulk samples in the 100° to 1100°C temperature range. For both phases, the A-group atoms, Al and Ge, vibrate with the highest amplitude and do so anisotropically within the basal plane. All bonds expand linearly with temperature, with the highest relative thermal expansion occurring in the Ti–Al and Cr–Ge bonds. The thermal expansion coefficients in the a - and c -direction are, respectively, 10.3(±0.2) × 10 −6 and 9.3(±0.2) × 10 −6  K −1 for Ti 2 AlN and 12.8(±0.3) × 10 −6 and 14.6(±0.3) × 10 −6  K −1 for Cr 2 GeC. The unit cell volume expansions observed by HTND are 10.0(±0.2) × 10 −6  K −1 for Ti 2 AlN and 13.4(±0.3) × 10 −6  K −1 for Cr 2 GeC.

Description: High surface area BiFeO 3 thin films were deposited on ITO substrates by templates method and chemical solution deposition. The resulting phase composition and microstructures were characterized using X-ray diffraction, scanning electron microscopy and Raman spectroscopy. We further demonstrated the useful photocatalytic activity of these films as determined by degradation of Congo red under visible-light irradiation ( λ 〉 400 nm). Our results showed that the surface area have a great effect on the photocatalytic performances of the BiFeO 3 thin films.

Description: We have developed a novel ion conductor comprising magnesium hafnium tungstate (MgHf(WO 4 ) 3 ) as a solid electrolyte for future metal-air batteries. The conductivity of this material measured as 2.5 × 10 −4 S/cm at 600°C is about one order of magnitude higher than that of existing ion conductor with similar structure, such as Sc 2 (WO 4 ) 3 . We have also elucidated for the first time that MgHf(WO 4 ) 3 has an intrinsic crystal structure, forming one-dimensional (1-D) alignments of individual Mg 2+ and Hf 4+ ions alternating within quasi-layered WO 4 2– units at Sc 3+ sites in Sc 2 (WO 4 ) 3 . The structure observed by HAADF-STEM clearly coincides with the results obtained by first principle calculation. The mechanism for high ion conductivity is discussed from the viewpoints of its ordered structure and physical property of negative thermal expansion.

Description: In the present work, compaction, sintering behavior, and mechanical properties of Al 2 O 3 –CeO 2 composite nanopowders were investigated. Al 2 O 3 and Al 2 O 3 –CeO 2 composite nanopowders were prepared by a sol–gel method. The effect of CeO 2 on compressibility, sintering rate, final density, and mechanical properties was studied. The aggregation strength of nanopowders reduced from 158 to 101 MPa by adding 5 wt% CeO 2 . The amount of CeO 2 had a strong effect on the sintering behavior and final microstructure of nanopowders and it inhibited alumina grain growth and suppressed densification process. The activation energy for grain growth increased from 428 to 554 kJ/mol by adding 5 wt% CeO 2 to the nanopowders. The addition of 5 wt% CeO 2 improved fracture toughness (by 28%) and flexural strength (by 17%) with respect to monolithic Al 2 O 3 .

Description: A 400-nm-thick (Pb 0.97 La 0.02 )(Zr 0.97 Ti 0.03 )O 3 (PLZT 2/97/3) antiferroelectric (AFE) thin films with different lead excess content (0%, 10%, and 20%) were successfully deposited on Pt(111)/TiO 2 /SiO 2 /Si substrates via a sol–gel process. The effects of lead excess content on the microstructure, dielectric properties, and energy storage performance of PLZT 2/97/3 AFE thin films were investigated in details. X-ray diffraction results displayed that AFE thin films were changed from the (111)-preferred orientation to the (100) and (111)-mixed orientation with increasing lead excess content. Dielectric measurements showed that AFE thin films with higher lead excess content exhibited enhanced dielectric constant and larger phase transformation fields. Thus, the energy storage density of AFE thin films was also remarkably improved from 3.3 to 11.7 J/cm 3 at 1200 kV/cm.

Description: Porous Si 3 N 4 ceramics with interconnected pores were fabricated by the phase separation method using benzoic acid (BA) as a pore-forming agent. The green bodies were prepared at room temperature under vacuum and pore-forming agent was quickly removed by sublimation below 200°C. The resulting porous green body exhibits uniform distribution of rod-like pores in the matrix. The porosity can be controlled by adjusting the BA content in Si 3 N 4 slurry. The flexural strength and fracture toughness of the porous Si 3 N 4 samples are in the range of 85–126 MPa and 1.08–1.7 MPa·m 1/2 with the porosity range of 57%–65.8%.

Description: In this work, we have prepared copper-doped multicomponent tellurite glasses by solid state electric field-assisted diffusion. The concentration profiles of the elements have been measured by the secondary ion mass spectrometry. The depth profile of copper can be well fitted only by a modified erfc-like solution of the second Fick's law which assumes that both the Cu + and Cu 2+ ions are involved in the diffusion. The modeling shows that the Cu 2+ ions are much more mobile than the Cu + ones in the tellurite glasses and affected strongly by the applied electric field. Our results demonstrate the possibility of fabricating copper-doped planar waveguides based on the tellurite glasses.

Description: By a self-organization process of alginate sol, alumina ceramic bodies with high porosity characterized by highly ordered and unidirectional oriented pores in the micrometer range were successfully fabricated with a 5–15 wt% solid loading range. The obtained porous Al 2 O 3 ceramics had a high total porosity over 70%, most (〉88%) of which were open pores, as well as an excellent permeability (K 〉 2.16 × 10 −11 m 2 ) and high compressive strength (〉15 MPa). The pore size, porosity, and thus the permeability and mechanical properties of the sintered ceramics can be effectively controlled by choosing different initial solid loadings.

Description: Networked ZnO nanowire sensors have been fabricated via selective growth of ZnO nanowires by the vapor growth method. The number of junctions per electrode pair (NJE) was deliberately controlled by changing the spacing of interdigital electrodes. Its effects on the sensing properties to NO 2 and CO were investigated. As the NJE increased, superior sensing properties were attained. This novel method to fabricate gas sensors using vapor-phase grown nanowires may circumvent the drawbacks of single nanowire gas sensors. Importantly, the NJE needs to be tuned to fully exploit networked nanowires in gas sensors.

Description: Perovskite Ba 0.6 Sr 0.4 TiO 3 (BST), pyrochlore Bi 1.5 Zn 1.0 Nb 1.5 O 7 (BZN), and hetero layered BZN/BST films have been directly grown on high resistivity (HR)-Si substrates by radio frequency magnetron sputtering. The microwave properties (up to 50 GHz) of all the films are evaluated by fabricating coplanar waveguide configuration. Experimental results showed that the BZN layer helped in tailoring the dielectric constant and reducing the loss tangent significantly. Moreover, the resulting BZN/BST/HR-Si films show moderate permittivity (~258) and tunability (~15.63%, 200 kV/cm), and low microwave loss (~0.0175) at 2 GHz and their microwave properties (1–50 GHz) potentially could be made suitable for integrated microwave tunable devices.

Description: Interaction between modified (K,Na)NbO 3 ceramics and metallic silver has been experimentally studied to simulate effects of using Ag-containing electrode pastes in multilayer actuators with alkali-based ferroelectric layers. The solubility limit of silver added as an excess component is found to vary in the range of 0.8–2.5 mol% depending on composition and stoichiometry of the ceramics. Inhomogeneous distribution of the residual undissolved silver across the thickness of a single ceramic layer between the co-fired Ag–Pd electrodes is evidenced by X-ray diffraction. The overall effect of Ag as excess component on temperature of the orthorhombic–tetragonal phase transition is found different from the known effect of Ag as alkali substituent.

Description: New lead-free perovskite solid solution ceramics of (1  − x )( Bi 1/2 Na 1/2 ) TiO 3 – x Ba ( Ni 1/2 Nb 1/2 ) O 3 [(1− x )BNT– x BNN, x  =   0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X-ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x  =   0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x  =   0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d 33 ~121 pC/N and k p ~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x  =   0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long-range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.

Description: Light transmission in polycrystalline magnesium fluoride was studied as a function of the mean grain size at different wavelengths. The mean grain size was varied by annealing hot-pressed billets in argon atmosphere at temperatures ranging from 600°C to 800°C for 1 h. The grain-size and grain-orientation distributions were characterized by electron back scatter diffraction. The scattering coefficients were calculated from the in-line transmittance measured at various wavelengths. The scattering coefficient of polycrystalline magnesium fluoride increased linearly with the mean grain size and inversely with the square of the wavelength of light. It is shown that these trends are consistent with theoretical models based on both a limiting form of the Raleigh–Gans–Debye (RGD) theory of particle scattering and light retardation theories that take refractive index variations along the light path. Quantitative predictions of the theories are, however, subject to uncertainly due to the restrictive assumptions made in the theories and difficulties in representing the microstructure in the theoretical models. In particular, grain-size distribution has a significant influence on the scattering coefficient calculated using particle scattering models.

Description: Determining the absolute chronology of ceramic artifacts has significant implications for archeological and historical research. Wilson, Hall et al . recently suggested a new technique for direct absolute dating of archeological ceramics based on a moisture-induced chemical reaction, called rehydroxylation (RHX) dating. RHX dating proceeds by measuring the mass of chemically combined water in the ceramics in the form of OH hydroxyls, and the mass gain rate at the Effective Lifetime Temperature (ELT) that the ceramics experienced over its lifetime. To date, ELT determinations have been based on estimates of the ceramic's lifetime temperature history; taking into account weather and climate data and the depth at which the artifact was found. The uncertainty in determining the ELT can be a major component of the overall dating uncertainty. Here, we propose an alternative method which relies minimally on weather and climate data, and provides more precise determinations of the ELT and the ceramic age . The proposed method (SAS: Same Age Samples) involves a minimum of four measurements of the RHX mass gain rate constant for two ceramic samples of the same age at two temperatures. We show via simulations that the proposed SAS method can determine the ELT with a precision of 0.2 K which is comparable to the best ELT determination based on lifetime temperature history, and also comparable to available microbalance temperature resolutions of around 0.1 K. The corresponding percent age error is then 1.4%, or 43 yr for a 3000-yr-old ceramic. The proposed SAS method should be tested with ceramic samples of different ages, whose ELT are well-known.

Description: Glasses in the Na 2 O–CaO–SrO–ZnO–SiO 2 system have previously been investigated for suitability as a reagent in Al-free glass polyalkenoate cements (GPCs). These materials have many properties that offer potential in orthopedics. However, their applicability has been limited, to date, because of their poor strength. This study was undertaken with the aim of increasing the mechanical properties of a series of these Zn-based GPC glasses by doping with nitrogen to give overall compositions of: 10Na 2 O–10CaO–20SrO–20ZnO–(40−3 x )SiO 2 – x Si 3 N 4 ( x is the no. of moles of Si 3 N 4 ). The density, glass-transition temperature, hardness, and elastic modulus of each glass were found to increase fairly linearly with nitrogen content. Indentation fracture resistance also increases with nitrogen content according to a power law relationship. These increases are consistent with the incorporation of N into the glass structure in threefold coordination with silicon resulting in extra cross-linking of the glass network. This was confirmed using 29 Si MAS-NMR which showed that an increasing number of Q 2 units and some Q 3 units with extra bridging anions are formed as nitrogen content increases at the expense of Q 1 units. A small proportion of Zn ions are found to be in tetrahedral coordination in the base oxide glass and the proportion of these increases with the presence of nitrogen.

Description: Despite the omnipresence of clay brick as construction material since thousands of years, fundamental knowledge about the link between composition, microstructure, and mechanical performance is still scarce. In this paper, we use a variety of advanced techniques of experimental mechanics and material characterization for extruded clay brick for masonry, that range from scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy, mercury intrusion porosimetry, to instrumented nanoindentation and macroscopic strength and durability tests. We find that extruded clay brick possesses a hierarchical microstructure: depending on the firing temperature, a “glassy” matrix phase, which manifests itself at submicrometer scales in form of neo-crystals of mullite, spinel-type phase, and other accessory minerals, forms either a granular or a continuum matrix phase that hosts at submillimeter scale the porosity. This porous composite forms the backbone for macroscopic material performance of extruded brick, including anisotropic strength, elasticity, and water absorption behavior.

Description: The fluorine and aluminum coordination environments and their evolution during precipitation of CaF 2 , SrF 2 , and (Ca x Sr 1− x )F 2 nanocrystals in oxyfluoride glasses and glass–ceramics are investigated using 19 F and 27 Al magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. These structural aspects of the parent glasses and of the resulting glass–ceramics are found to be strongly dependent on the nature of the modifier cation. In the calcium-modified glass the preexisting F–Ca( n ) sites act as major precursors of F–Ca(4) sites in CaF 2 nanocrystals that are precipitated upon ceramming. In contrast, for the strontium-modified glass, besides F–Sr( n ) sites a large fraction of the Al–F–Sr( n ) sites in the parent glass are converted into F–Sr(4) sites in the glass–ceramic during precipitation of SrF 2 nanocrystals. In the case of a glass containing both calcium and strontium as modifying cations precipitation of (Ca x Sr 1− x )F 2 solid solution nanocrystals is achieved upon ceramming. However, Ca 2+ ions preferentially partition into the crystal phase resulting in a Ca:Sr atomic ratio that is significantly higher in the nanocrystal compared with that in the parent glass. These observations are consistent with the higher field strength of Ca 2+ compared with Sr 2+ . Incorporation of Yb 3+ ions into the lattices of these fluoride nanocrystals is also evidenced in the 19 F NMR spectra.

Description: Cation-stoichiometric and strontium-deficient Sr 1− x Ce x TiO 3 ±δ (0〈 x 〈0.15) have been appraised using controlled-atmosphere dilatometry, thermogravimetric analysis, and measurements of total conductivity and Seebeck coefficient in the oxygen partial pressure range from 10 −20 to 0.5 atm at 650°–950°C. As for other donor-doped titanates, perovskite-type Sr 1− x Ce x TiO 3 ±δ exhibit predominant n -type electronic conductivity and slow changes in the charge-compensation mechanism on reduction, associated with kinetically stagnated diffusion. The resultant hysteresis and kinetic stabilization of nonequilibrium states make it possible to substantially increase the conductivity by preliminary reduction at high temperatures, such as 1350°C. Owing to relatively small variations in the defect concentrations, the chemically induced expansion of Ce-substituted titanate ceramics is very low, while the thermal expansion at 130°–1100°C is almost linear and essentially independent. The average thermal expansion coefficients vary in the narrow range (11–12) × 10 −6 K −1 , compatible with common solid oxide electrolytes. All of these properties make the material an attractive choice as a solid oxide fuel cell anode material. However, the nature of the reduced, highly conductive, state appears to be metastable and may not be completely recoverable after redox cycling.

Description: The Eu 2+ -doped NaBaPO 4 phosphor was prepared by high-temperature solid-state reaction. The photoluminescence excitation and emission spectra and the luminescence quantum efficiency of Eu 2+ ions were investigated. The dependence of luminescence intensity on temperatures and the temperature-dependent decay times of Eu 2+ ions doped in NaBaPO 4 were measured and discussed. The natures of the Eu 2+ emission in NaBaPO 4 , e.g., the Stokes shift, the luminescence quenching temperature ( T 0.5 ), the activation energy for thermal quenching (δ E ) were reported. In addition, the crystal structure and the site occupancy of Eu 2+ ions doped in NaBaPO 4 crystal lattice were discussed. Two different Eu 2+ centers were assigned according to the crystal structure and the luminescence characteristics of Eu 2+ ions. The phosphor shows an excellent thermal stability on temperature quenching effects. With the increasing of temperature, the emission bands show the abnormal blue-shift.

Description: We have synthesized high-purity Yb 3+ -doped Lu 2 O 3 powder by the coprecipitation method. We have demonstrated that the recrystallization of the metal nitrates greatly improve the chemical purity of the resulting oxides. From thermogravimetry and differential thermal analysis study, we have calculated the approximate formula of the oxinitrate precipitate precursor as Lu 1.8 Yb 0.2 (OH) 5.44 (NO 3 ) 0.56 ·0.58H 2 O. Fine and soft agglomerate powders were obtained after calcinations. We have shown that the powder is mainly in the form of polycrystalline soft agglomerates composed with 15–20 nm size crystals. The resulting ceramic showed higher transparency (close to theoretical limit) compared with the ones fabricated with commercial powders.

Description: β-Ga 2 O 3 nanobelts have been synthesized by a vapor transport process under different ambient oxygen. Their structural and optical properties were characterized by field-emission scanning electron microscopy, X-ray diffraction, photoluminescence (PL), and absorbance measurements. Structural characterization revealed that the as-synthesized samples consist of monoclinic β-Ga 2 O 3 nanobelts with comparable surface area. Samples prepared under high oxygen ambient possessed large numbers of gallium-associated defects confirmed by PL and absorbance measurements. The photocatalytic activity of β-Ga 2 O 3 nanobelts was evaluated by the degradation of organic dyes (rhodamine B and methyl blue) under ultraviolet light illumination. The results demonstrated that β-Ga 2 O 3 nanobelts exhibited superior photocatalytic activity and stability as compared with commercial β-Ga 2 O 3 powder. The photocatalytic activity of β-Ga 2 O 3 nanobelts was greatly enhanced and attributed to the large numbers of acceptor states associated with gallium defects. The origin of enhanced photocatalytic activity of β-Ga 2 O 3 nanobelts was discussed.

Description: In conventional process of ceramic injection molding, wax-based binders could only be removed by thermal or organic solvent debinding. Recently, water solvent debinding has appeared as a good alternative owing to its high efficiency and environmental friendliness. In present work, we have demonstrated the surface modification mechanism of stearic acid (SA) to zirconia powders induced by a prior ball-milling treatment before the blending process. Layers of SA with various thicknesses coated around the zirconia powders have been achieved with different amount of SA after the treatment, agreeing well with the theoretically calculated values. The coating is disclosed to be an esterification occurring between the carboxyl group of SA and hydroxyl group of zirconia surface. It plays an important role in limiting agglomeration of ceramic powders and changing the nature of powder surface from hydrophilicity to hydrophobicity, which decreases the shear viscosity of the feedstock and makes the water-debound compact process-compatible with few phase separation. In addition, a significantly faster water-debinding rate was obtained.

Description: 0.90(Na 0.5 Bi 0.5 TiO 3 )–0.06BaTiO 3 –0.04K 0.5 Na 0.5 NbO 3 (NBT–BT–KNN) polycrystalline ferroelectric thin films were prepared on Pt-coated silicon substrates by a chemical solution deposition method. Cracks were eliminated by reducing the residual stress and single perovskite phase was realized by eliminating pyrochlore second phase when the precursor solution was modified with polyethylene glycol (PEG). The obtained NBT–BT–KNN ferroelectric thin films exhibited a large strain of 0.22% and an effective piezoelectric coefficient d 33 of 78 pm/V under the clamping of the substrate. The results indicate that the NBT-based thin films are a potential candidate as a lead-free piezoelectric material for microsystems.

Description: The optical properties and microstructure are evaluated for a transparent cubic (8 mol% yttria-stabilized) zirconia ( c -YSZ) prepared by high-pressure spark plasma sintering. Oxygen vacancies and residual pores are primary defects in the present transparent c -YSZ, and the combination influence of these two defects determines the optical properties. The as-sintered transparent zirconia strongly absorbs the incident light due to the formation of high concentration of oxygen vacancies. Annealing treatment in oxidizing atmosphere can improve the transparency by reducing oxygen defects. The existence of fine pores in the present zirconia causes scattering of the incident light.

Description: Recent studies on the mechanical compliance measurements of plasma-sprayed ceramic coatings have revealed anelastic response, i.e. the stress–strain relations are nonlinear and hysteretic, collectively. The anelasticity stems from the “brick” layered assemblage of spray-deposited droplets along with the presence of porosity and other geometric discontinuities. This anelastic response is reproducible and can provide a quantitative description on the mechanical properties of the sprayed ceramic coating. In this paper, we have examined strategies to manipulate and control these anelastic characteristics through plasma spray processing parameters as well as through extrinsic modifications of the defect interfaces. Plasma-sprayed ceramic coatings are fabricated under various conditions and their unique anelastic parameters are computed. These results reveal that the novel properties are tunable via process and material manipulation, opening up opportunities for microstructural design and optimization of mechanical compliance in industrially relevant coating systems.

Description: A microwave-assisted hydrothermal route was developed for preparing (Sr 1− x − y Ce x Tb y )Si 2 O 2−δ N 2+μ phosphors. Both the required calcination temperatures and heating duration were markedly reduced as compared with the solid-state reaction. With a rise in the calcination temperatures, the emission intensity of Ce 3+ -doped phosphors decreased due to the thermal quenching effects. For Tb 3+ -doped phosphors, the emission intensities of the splitting peaks were influenced by the thermal interaction between the Tb 3+ energy levels. It is found that the Ce 3+ - and Tb 3+ -doped SrSi 2 O 2 N 2 phosphors demonstrate great absorption in the vacuum ultraviolet region and are therefore suitable for application in plasma display panels. While Ce 3+ and Tb 3+ were codoped into SrSi 2 O 2 N 2 , the emission spectra exhibited the combination of the Ce 3+ and Tb 3+ emission peaks. The energy transfer process from Tb 3+ to Ce 3+ via the electrostatic interaction was also investigated in detail.

Description: Pattern recognition techniques were used to extract features from the density of states (DOS) curves derived from density functional theory calculations of over a dozen related oxide systems. Features in the DOS profiles that were associated with crystal structure, chemistry, and stoichiometry were identified. Classification maps identifying trends in the electronic structure with respect to crystal chemistry were created using multivariate analysis methods. It was found that crystal structure appeared to have a more significant impact on the DOS than chemistry for the systems studied. The differences in the electronic structure of HfO 2 and ZrO 2 were captured as a function of crystal structure, and the features of the DOS curve, which represent these differences, were identified. Correlations between crystal symmetry and metal/oxygen ratio were also uncovered from this type of analysis.

Description: The effect of Nb 2 O 5 addition on impulse aging behavior of ZnO–V 2 O 5 –MnO 2 –Co 3 O 4 –Dy 2 O 3 -based varistors was investigated. The varistors doped with 0.25 mol% Nb 2 O 5 exhibited the best clamp characteristics, in which the clamp voltage ratio was in the range of K =1.65–2.50 at an impulse current of 1–50 A. The varistors doped with 0.1 mol% Nb 2 O 5 exhibited the best electrical stability by marking %Δ E 1 mA =−1.0%, %Δα=−2.8%, and %Δ J L =31.5% after applying the impulse current of 100 A.

Description: The calcium phosphate family of biomaterials includes numerous compounds that might find applicability in orthopedics and dentistry as implant materials. However, only calcium phosphates of higher Ca:P ratio such as hydroxyapatite and tricalcium phosphates have been exposed to extensive investigations. Reports on the biomedical application of calcium phosphates with lower Ca:P ratios are sparse. The condensed calcium phosphates ([Ca(PO 3 ) 2 ] n -Ca:P=0.5) represent such material. In the present work, calcium polyphosphate (CPP) with Ca:P=0.5 was synthesized and CPP scaffolds were fabricated. The synthesized polymorphic CPP powder was characterized for its chemical prosperities using X-ray diffraction, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy techniques and the fabricated scaffolds were tested in MC3T3 (murine osteoblast) cells for their biocompatibility. Cell viability test results indicate that CPP did not exert cytotoxicity effect on the cells after being cultured 21 days. CPP sintered at 1100°C showed better cell attachment and proliferation. The results obtained in the present work demonstrate the suitability of CPP as potential scaffold material for translocation of cells.

Description: Ferrous and ferric phosphate crystalline compounds and glasses were studied using Raman spectroscopy. A comparison of the spectra from crystalline and glassy ortho-, pyro-, and metaphosphates indicates that similar phosphate anions constitute the structures of the respective materials, and some information about the compositional dependence of the phosphate-site distributions in the glasses can be gleaned from relative peak intensities. A correlation exists between the average P–O bond distance and the Raman peak frequencies in the crystalline compounds, and this correlation is used to provide information about the structures of the iron phosphate glasses. For example, the average P–O bond distance is estimated to decrease from about 1.57 Å for iron metaphosphate glasses (O/P∼3.0) to 1.54 Å for iron orthophosphate glasses (O/P∼4.0). These bond distances are in good agreement with those reported from diffraction studies of similar glasses.

Description: Various lead-free (K x Na 1− x ) 0.98 Li 0.02 (Nb 0.82− y Ta 0.18 Sb y )O 3 ceramics with x =0.50, y =0.00–0.07 or x =0.40–0.60, y =0.05 were prepared by the conventional solid-state reaction method. Systematic investigation on the microstructures, crystalline structures, and dielectric and piezoelectric properties was carried out. Remarkably strong piezoelectricity has been achieved in (K 0.45 Na 0.55 ) 0.98 Li 0.02 (Nb 0.77 Ta 0.18 Sb 0.05 )O 3 ceramic, which shows the excellent piezoelectric properties of d 33 =413 pC/N, d 31 =−153 pC/N, k p =0.50, and k 33 =0.62. It is considered that the observed strong piezoelectricity should be ascribed to several combined decisive factors, such as the phase coexistence due to an orthorhombic–tetragonal polymorphic phase transition near room temperature, the high electronegativity of Sb 5+ ions as compared with those of Nb 5+ ions and Ta 5+ ions, and the relatively ideal microstructure with high density, large average grain size and narrow grain-size distribution.

Description: The sinterability of high-purity, nanocrystalline Y 2 O 3 without any additives was investigated by spark plasma sintering (SPS) for a combination of low sintering temperatures (850°–1050°C) and low heating rates (2–50°C/min). At a sintering temperature of 950°C and a heating rate of 2°C/min, the SPS yielded a polycrystalline Y 2 O 3 having a relative density of 99% and an average grain size of 190 nm. The Y 2 O 3 bodies sintered at 950° and 1050°C for 1h at the heating rate of 2°C/min exhibited an in-line transmittance of 6%–46% in a wavelength range of 400–800 nm. A high-resolution transmission electron microscopy observation and chemical analysis by an energy-dispersive X-ray spectrometer revealed that the sintered Y 2 O 3 bodies were single-phase materials without any grain-boundary amorphous layer or impurity contamination. An isothermal SPS experiment indicated that the grain-boundary mobility is significantly enhanced by the SPS. An electron energy loss spectrometry indicated that SPS changed atomic configuration of the grain boundaries. The improved sinterability of Y 2 O 3 is attributed to the enhanced diffusion that arises from defect reactions activated by the SPS.

Description: Aerosol deposition method was used as an alternative deposition technique in crystalline electrolyte deposition process. Crystalline Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 thick layers were successfully deposited on stainless-steel substrates and X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, and AC impedance techniques were used to characterize these films. The density of the deposited films was between 83% and 86% of the theoretical density and Vickers hardness was calculated to have values between 260 and 280 Hv. Bulk and total conductivities were 3.62 × 10 −3 and 1.12 × 10 −6 S/cm, respectively, and DC conductivity was 〈10 −10 S/cm for a wide range of film thicknesses. Improvement in total conductivity of the Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 samples is still needed to make these films more suitable for all-solid-state Li-ion batteries.

Description: (Co, Nb, Sm)-doped SnO 2 -based ceramic with varistor characteristics was successfully fabricated by a conventional sintering of nanosized (Co, Nb, Sm)-doped SnO 2 powders prepared by coprecipitation method. Values of α∼38 and E B =1430 V/mm were obtained for the varistor doped with 0.05 mol % Sm 2 O 3 , sintered at 1200°C for 1 h. Microstructure development was studied by scanning and transmission electron microscopy, elemental analysis, and X-ray diffraction. The mean grain size of the SnO 2 -based varistor was 1.75 μm. No other phase besides SnO 2 was observed in the varistor doped with 0.05 mol % Sm 2 O 3 . The presence of Nb, Co, and Sm inside the SnO 2 grains confirmed the formation of solid solution. No segregation of Nb was observed and Nb atoms were homogeneously distributed. The excess amounts of Co were segregated at triple-junctions between SnO 2 grains. A Sm-rich region with a typical thickness of 65 nm was observed at the grain boundary of the varistor.

Description: Hydroxy sodalite (HS) particles were synthesized hydrothermally at 90°C for 10 h in the presence of cetyltrimethylammonium bromide (CTAB) and other aqua-based precursor materials like sodium aluminate, sodium metasilicate, and water. Crystalline phases and microstructures of the synthesized particles were studied by X-ray diffraction and field emission scanning electron microscopy, respectively. The effect of CTAB concentrations on the crystallinity and morphology of the synthesized particles was investigated. Thread-ball like HS particles along with some cube-shaped zeolite A were obtained in the presence of 0–0.5 mM CTAB while flower-like HS particles were observed in the presence of 1–5 mM of CTAB concentrations. With increase in CTAB concentration, HS phase increased significantly, and phase pure HS particles resulted for 3 and 5 mM of CTAB concentrations. A mechanism for the formation of flower-like HS particles was also proposed.

Description: In engineered systems where thermal strains and stresses are limiting, the ability to tailor the thermal expansion of the constituent materials independently from other properties is desirable. It is possible to combine two materials and space in such a way that the net coefficient of thermal expansion (CTE) of the structure is significantly different from the constituents, including the possibility of zero and negative thermal expansion. Bimaterial lattices that combine low, negative, or an otherwise tailored CTE with high stiffness, when carefully designed, have theoretical properties that are unmatched by other known material systems. Of known lattice configurations with tailorable CTE, only one geometry, a pin-jointed lattice, has been shown to be stretch dominated and thus capable of having stiffness that approaches its theoretical upper bound. A related lattice with bonded joints, more amenable to fabrication, is developed that has a stiffness and CTE similar to the pinned structure. Analytical models for this rigid-jointed lattice's CTE and stiffness are developed and compared successfully with numerical results. A near space-filling, negative thermal expansion version of this lattice is devised and fabricated from titanium and aluminum. CTE measurements on this lattice are made and are well predicted by the analytical and numerical models. These insights guide the design of a family of bonded lattices with low areal density, low or negative CTE, and high stiffness to density ratio. Such lattices are shown to have a thermomechanical response that converges on pin-jointed behavior when the lattice elements are long and slender.

Description: The solid solution of a (1− x )PbZrO 3 – x Pb(In 1/2 Nb 1/2 )O 3 (PZ–PIN) system, with x =0.00–0.50, was synthesized using the wolframite precursor method. The effects of the PIN content on the crystal structure, and the electrical and thermal properties of a PbZrO 3 ceramic were investigated using X-ray diffraction, dielectric spectroscopy, hysteresis measurement, and differential scanning calorimetry techniques. Furthermore, the morphology and grain size were determined using scanning electron microscopy. The results indicated that the pure perovskite phase was obtained for all compositions, and the solid solution, PZ–PIN, changed from orthorhombic to rhombohedral symmetry when the amount of PIN increased. A ferroelectric intermediate phase began to appear between the paraelectric and the antiferroelectric phases of pure PZ, with increasing PIN content. The temperature range width of the ferroelectric phase also increased continuously with increasing PIN. At room temperature, the polymorphic phase transition (PPT) was identified from the orthorhombic to the rhombohedral phase in (1− x )PZ– x PIN at the composition, x =0.40. The ceramics ( x =0.40) with PPT close to room temperature exhibited excellent electrical properties (ɛ rmax =33240 and P r =26.94 μC/cm 2 ).

Description: Piezoelectric ceramics of the composition Na 0.5 K 0.5 NbO 3 (NKN) with grain sizes in the range of 0.2–1 μm were fabricated by spark plasma sintering. Ferroelectric domain size decreases with decreasing grain size and non-180° ferroelectric domains walls were still visible in 200 nm sized grains. The Curie point of the ceramics was grain size independent. This suggests that the critical grain size for a single domain single grain structure for NKN is 〈200 nm. Optimized processing conditions enabled ceramics of high densities (〉99.5% theoretical density) to be made at T ≥850°C. For the dense ceramics (grain size ≥350 nm), the room temperature dielectric constant and coercive field increased with decreasing grain size. The remnant polarization was grain size independent. The material sintered at 850°C is a very good candidate for lead-free piezoelectric applications because of its high piezoelectric constant ( d 33 =160 ± 2 pC/N).

Description: The phase transition and pyroelectric behavior of Na y Bi z Ti 1− x O 3(1− x ) – x BaTiO 3 ( x =0.06–0.08, z / y ≧1) ceramics were investigated as functions of temperature and electric field. A dominant antiferroelectric (AFE) ground state is proposed for Na y Bi z Ti 1− x O 3(1− x ) – x BaTiO 3 ( x =0.06–0.08, z / y ≧1) ceramics at room temperature (RT). The stability of the induced ferroelectric (FE) phase is closely related to the molar ratio of Na + and Bi 3+ . The temperature of the FE to AFE phase transition for the poled samples can be adjusted to RT through a modulation of the molar ratio of Na + and Bi 3+ . Pyroelectric current peaks were detected at the FE–AFE transition temperature. Huge pyroelectric coefficients of 905 × 10 −8 , 3270 × 10 −8 , and 140 × 10 −8 °C·(cm 2 ·K) −1 were obtained at phase transition temperatures of 83°, 64°, and 34°C, respectively.

Description: Preparation of Li 1− m Ag m La 0.99− n Y n Pr 0.01 ( MoO 4 ) 2 phosphors was done by a convenient method of solid-state reaction technique in the air. The effects of synthesis temperature, substitution of Ag + , Y 3+ on the LiLa ( MoO 4 ) 2 crystal structure, and luminescence properties of Pr 3+ in the molybdate host are investigated systematically. The observed excitation and emission spectra indicate that the phosphor can be excited effectively by the blue light (440–500 nm) and exhibit a satisfactory red emission at 605 and 649 nm, respectively. The substitution of a little Ag + for Li + enhances the Pr 3+ luminescence intensity drastically. The variability of Y 3+ and La 3+ content changes the emission intensity ratio of the 1 D 2  →  3 H 4 and 3 P 0  →  3 F 2 transition, so that the CIE chromaticity coordinates of the as-prepared Li 1− m Ag m La 0.99− n Y n Pr 0.01 ( MoO 4 ) 2 phosphors are tuned from (0.639, 0.351) to (0.653, 0.337).

Description: The effect of loading rate on indentation hardness, brittleness, and fracture modes during static and dynamic Vickers indentation of a transparent coarse grain (250 μm average grain size) polycrystalline magnesium aluminate spinel was investigated. Static hardness was measured using a conventional Vickers tester while the dynamic hardness was measured using a custom test fixture based on split Hopkinson pressure bar technique with the capability to produce single indentations at strain rates of roughly 10 3  s −1 . Static and dynamic hardness values as well as characteristic fracture response are compared at a range of indentation loads. It was found that Vickers micro hardness increased by an average of 5% over the entire load range, while the calculated brittleness factor increased when subjected to dynamic indentation loads. Static and dynamic indentations were found to produce radial and lateral cracks with evidence of spall appearing only during dynamic loading. Dynamic indentations also revealed an increased level of transgranular cracking, whereas intergranular cracking was more dominant during static indentations. Indentation cracks generated due to static indentations placed in the vicinity of a grain boundary deflected along a grain boundary, whereas these cracks cut across the grain boundary into the neighboring grain during dynamic indentations. Static and dynamic indentations that were placed directly on grain boundaries generated intergranular (grain boundary) cracks that were on average 18% longer than accompanying intragranular cracks. The implications of these fracture modes on dynamic impact response of polycrystalline spinel are discussed.

Description: We present a new approach to the synthesis of inorganic coatings based on the ability of cultured cells to actively uptake large amounts of nanoparticles. The cellular matrix allows maintaining the adhesion of the nanoparticles to the substrate at temperatures high enough to allow bonding of the powders on the substrate during a subsequent thermal degradation. Exploiting different cell abilities it is possible to obtain patterning and formation of nanocomposites even on substrates characterized by complex geometries. These results suggest that cultured eukaryotic cells have good potential as a tool for the realization of inorganic coatings.

Description: The local structure of cerium in two systematic compositional series of glasses, nominally CeP 3 O 9 –AlP 3 O 9 and CeP 3 O 9 –SiP 2 O 7 , was interrogated using X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy. XPS revealed that, for glasses melted in air, ≥95% of cerium ions are Ce 3+ . This was independently confirmed using X-ray absorption near edge spectroscopy (XANES). Ce K-edge extended X-ray absorption fine structure (EXAFS) has been used to determine the local structure of Ce 3+ . Near the metaphosphate composition, cerium was found to have an average cerium coordination number of ~7.0 and an average cerium-oxygen bond length of 2.41 Å. The average cerium coordination number and average cerium-oxygen bond distance were found to increase with decreasing cerium concentration in both compositional series. Rare-earth clustering is suggested based on numerical calculations for glasses containing ≥14 and ≥15 mol% Ce 2 O 3 for the aluminophosphate and silicophosphate series, respectively.

Description: Fabrication of Si 2 N 2 O phase free, fully densified Si 3 N 4 / SiC nano–nano composite ceramics was done by combining a carbothermal reduction treatment (CRT) and a spark plasma sintering (SPS) using commercially available Si 3 N 4 and SiC nano-powders, and their mechanical and tribological properties were investigated. CRT was conducted at 1450°C for 10 h with a phenolic resin and SPS was carried out at 1550°C for 5 min, which yielded the fully dense (〉98% of theoretical density) Si 3 N 4 / SiC nano–nano ceramics with ~100 nm grain size. The elastic modulus, hardness, and fracture toughness increased with increasing SiC content up to 20 wt%. The wear rate of Si 3 N 4 / SiC nano–nano ceramics decreased from 2.0×10 −5 to 6.76×10 −6  mm 3 /Nm with 20 wt% SiC addition, resulting from the increased hardness and fracture toughness.

Description: The fabrication of a three-dimensionally structured metal oxide on various substrates mediated with self-assemble monolayer (SAM) Au -precoated substrates, such as Si wafer, non-planar glass, and flexible plastic, is important for a number of practical applications in electronics, photonics, and biotechnology. In this report, we describe the use of transfer printing for forming three-dimensionally structured TiO 2 thin films with feature sizes of 10 μm in the diameter and 3 μm in height over areas of several square millimeters by direct patterning onto Si surfaces. This process is mediated by the presence of a 3-mercaptopropyltrimethoxysilane monolayer that guides the transfer of three-dimensionally structured TiO 2 thin films from the low-energy surfaces of the mold to a Si substrate via surface forces.

Description: We found that the nano-sized Y 3 Fe 5 O 12 powder prepared by bead milling has the highest heat generation ability in an AC magnetic field of reported superparamagnetic materials. The heat generation ability in an AC magnetic field was strongly improved by a decrease in the average crystallite size of the bead milled samples. The highest heat ability in the AC magnetic field was for the fine Y 3 Fe 5 O 12 powder with ca. 15 nm crystallite size (the samples milled for 4 h using 0.1 mmφ beads). The reasons for the high heat generation properties of the milled samples are ascribed to an increase in the Néel relaxation of the superparamagnetic material. The heat generation ability (W·g −1 ) can be estimated using a 3.58 × 10 −4  f·H 2 frequency (f/kHz) and the magnetic field (H/kA·m −1 ) for the sample milled for 4 h using 0.1 mmφ beads.

Description: A novel and general process for the fabrication of porous ceramics and metal/ceramic/polymer nanocomposites by freeze-photocuring-casting (FPC) is presented. The homogenous fluid containing water, curable monomers, and colloidal particles is frozen, and the phase separated microstructure is fixed by photo-initiated polymerization. At the relatively high resin/particle ratio explored here, the structure is sufficiently strong to withstand the capillary forces during ambient drying; however, it is capable of transforming to macroscopic ceramics such as Al 2 O 3 and SiO 2 by conventional debinding and sintering. The use of FPC fluids enables producing porous macroscopic shapes such as microspheres, films, and multilayer coatings having an ordered, interconnected pore network and pore sizes down to the low sub-micrometer range. The pore structure is found to be dependent on the radius of curvature of the macroscopic structure. Ag–TiO 2 /polyacrylate porous nanocomposites are produced by co-shaping of FPC containing sterically stable colloids, soluble metal salts, and monomers. Ag nanoparticles form in situ by reduction of Ag + ions on the TiO 2 surface. This triggers the photo-polymerization of the resin without the need of a photoinitiator. It is found that if the cured layers in a multilayer stack are frozen before the newly deposited layer, the ice crystal structure formed is linked via epitaxial growth.

Description: Er -doped and Yb,Er -doped CeF 3 –CaF 2 disordered crystals were grown by temperature gradient technique (TGT) method. The UV–VIS–NIR absorption spectra, near-infrared emission spectra, and the lifetime of 4 I 13/2 level were measured. The infrared to visible upconversion emission of Er 3+ was investigated in the grown crystals. The concentration distribution of doped ions was analyzed using ICP measurements. The efficiency of energy transfer from Yb 3+ ( 2 F 5/2 ) to Er 3+ ( 4 I 11/2 ) was about 88%. The experimental luminescence lifetime of the ~1.5 μm emission for CeF 3 –CaF 2 : Yb,Er crystal was 3.84 ms, and its quantum efficiency was 79%.

Description: An approach to synthesize bulk nanostructured titanium boride ( TiB ) ceramic material having a whisker-like microstructure with a very attractive combination of mechanical properties is presented. The material is made of a three-dimensional network of high aspect ratio TiB whiskers that are created in situ during reaction sintering of micron-sized component powders at pressures of 15–20 MPa and at relatively low temperatures (〈1400°C). It is shown that the properties are sensitive to the amount of titanium used in the reaction-sintering process. The mechanism of formation of nanostructured TiB whiskers and the process of densification, both facilitated by tri-modal powder particle packing and liquid/β-phase regions, are illustrated. Mechanical property evaluations indicate that, unlike conventional nanoceramics, a good combination of hardness, strength, and toughness can be achieved by the control of microstructure. For example, the best TiB composition synthesized here resulted in a Vickers hardness of 16 GPa, an elastic modulus of 425 GPa, a mean flexural strength of 800 MPa, and a SEPB fracture toughness of 5.2 MPa√m. This combination of properties, from the perspective of room temperature applications, places the material on par with certain grades of silicon nitride (Si 3 N 4 ) indicating that the material offers significant potential for further development.

Description: A superfine leucite-reinforced dental material was prepared by heat-treating the mixture of hydrothermally derived leucite precursor and low-temperature frit at 750°C. XRD and DSC results indicate that the low-temperature frit can lower leucite crystallization temperature from 1027°C to 694°C. High-temperature X-ray diffraction of the dental porcelain demonstrates that there exists a temperature range in which leucite crystals are in the equilibrium of forming, ripening, and dissolving, and the size and content of leucite remain almost unchanged in the range. The average size of leucite in the dental porcelain prepared by the mixture of low-temperature frit and the material is about 115 nm, which would benefit PFM's strength.

Description: PZT films were deposited by the sol-gel method on platinized silicon substrates with silicon nitride and silicon oxide structural layer materials. The crystalline orientations of the PZT films were controlled by both a chelating agent and pyrolysis temperature. A nanoindentation CSM (continuous stiffness measurement) technique was utilized to characterize the Young's moduli of these PZT films. It was found that the measured moduli of PZT films on the two types of substrates showed similar orientation dependence ( E 001  〉  E 111 〉 E (110,111) ) but distinct values, which indicated a clear substrate effect. By using a new model of film indentation, we were able to decouple the effects of film orientation and structural layer type on the Young's modulus.

Description: Surface energy of cerium oxide was measured by differential scanning calorimetry (DSC). Nanocrystalline CeO 2 samples were synthesized by a nonaqueous sol–gel method and their surface and interfacial areas were determined from nitrogen adsorption, X-ray diffraction, and electron microscopy measurements. Three samples were repeatedly heated in a differential scanning calorimeter and the excess enthalpy was obtained from the difference in DSC traces between first heating, during which coarsening occurred, and second heating. Surface enthalpy was calculated from excess enthalpy and from changes in surface and interfacial areas. The measured surface enthalpy for CeO 2 , 1.2 ± 0.2 J/m 2 , is consistent with values from oxide melt solution calorimetry on samples with different surface areas. This is the first successful measurement of surface energy using scanning calorimetry.

Description: The ZrB 2 powders with submicrometric particle size and low oxygen content were synthesized by a new borothermal reduction route using ZrO 2 and excess boron as raw materials. The conventional process only contained the borothermal reduction of ZrO 2 with boron at 1550°C. By exploring the mechanism of ZrB 2 particle coarsening during conventional process, a new borothermal reduction route was proposed. This route included the borothermal reduction of ZrO 2 with boron at 1000°C, washing by hot water, and the removal of residual boron oxides at 1550°C, namely, two-step reduction plus intermediate water-washing (RWR). Using conventional process, the particle size and oxygen content of ZrB 2 powder were about 2–3 μm and 0.68 wt%, respectively. Based on the new route, the particle size and oxygen content of ZrB 2 powder were about 0.4–0.7 μm and 0.40 wt%, respectively.

Description: A modified resonant cavity method was developed to measure the dielectric properties of ferroelectric ceramics at microwave frequencies, which were difficult to be evaluated accurately because of the high dielectric constant and high dielectric loss. With the aid of low-loss reference ceramic, the dielectric constant and dielectric loss of the small-sized ferroelectric ceramic sample could be measured accurately from the difference between the resonant peaks (TE 01δ mode) with and without introducing the to-be-determined sample. The microwave dielectric properties of Pb(Zr 0.52 Ti 0.48 )O 3 , Ba 0.5 Sr 0.5 Nb 2 O 6 , and BaTiO 3 ferroelectric ceramics were measured between 3.4 and 4.9 GHz using this method, together with the temperature dependence.

Description: In the present study, fiber-matrix compatibility in an all-oxide ceramic composite is examined. Reaction-bonding aluminum oxide is used as porous matrix to ensure weak interfaces with fibers. Matrix cracks have been deflected around the interface for sintering temperatures up to 1300°C, due to the effectiveness of porous matrix in enabling damage tolerance. Above 1300°C, densification of the matrix resulted in brittle fracture of the samples, with matrix cracks going through the fibers. Observation of fracture surfaces confirmed the fiber pull-out phenomenon up to processing temperatures of 1300°C. The well-known He and Hutchinson criteria for crack deflection was used to predict debonding behavior at the fiber-matrix interface as a function of matrix porosity. Furthermore, evaluation of the microstructure evolution of Nextel ™ 610 alumina fibers showed a pronounced grain coarsening at sintering temperatures above 1300°C. Changes in crack deflection behavior and fiber microstructure of a composite sample aged for 100 h are also presented.

Description: The mechanical properties of partially wick-debinded, Al 2 O 3 -based ceramic parts, prepared by low-pressure injection molding have been investigated. These properties depend on the residual paraffin wax binder content and on the chemical nature of the binder, which changes drastically if the wick-debinding takes place in air at a temperature above 190°C. Under these conditions, the paraffin binder undergoes a transformation, as a result of complex exothermic chemical reactions with oxygen. Part of it forms volatile products, while the remaining part cures into a nonvolatile, brown-colored, solid substance, which resides in the wick-debinded part and bonds the powder particles firmly together. The curing can be beneficial, as strong wick-debinded parts with bending strengths up to 14 MPa, containing less than 2% of the residual binder, can be obtained without flaws. The strength of the partially debinded parts increases with the dwelling time at 200°C, whereas the binder content reaches a minimum value of about 1.6% and then remains constant with the dwell time. Strong debinded parts can be easily manipulated and can be rapidly sintered due to the low amount of the residual organic phase.

Description: Over the past decade, multilayer ceramic capacitors (MLCCs) have been able to achieve very high volumetric capacitance due to continuous improvement in their process technology. However, the performance of these devices is severely limited by the presence of electrode defects such as electrode porosity and roughness. To assess the effect of microstructure on MLCC performance, two sets of multilayer capacitors subjected to different processing conditions are compared for their microstructure and electrical properties. It is shown that more continuous and planar electrode morphology leads to lower local electric fields and thus, superior performance. These computational predictions are verified using electrical property measurements. Capacitors with higher electrode continuity exhibit proportionally higher capacitance, provided the grain-size distributions are similar. From the leakage current measurements, it is found that the Schottky barrier at the electrode–dielectric interface controls the conduction mechanism. This barrier height is adversely affected by the microstructural defects such as electrode discontinuities and roughness. These results are further supported by frequency-dependent impedance measurements.

Description: New types of bulk SiOC glass matrix composites reinforced with diamond particles were successfully fabricated. Diamond particles were introduced into the SiOC matrix by the polymer-derived ceramics (PDC) route using polysiloxane and two different sized diamond particles, 2 and 30 μm as starting precursors. Dense bulk specimens were prepared by warm pressing at 150°C–160°C followed by pyrolization at 1100°C for 2 h. The composites were characterized by means of SEM, TEM, optical observation, X-ray diffraction, and Vickers indentation. Elastic properties were determined by means of ultrasonic echography, and Young's modulus was found to increase from 96 to 154 GPa when diamond content increased from 0 to 25 vol%. Reinforcement results in significant improvement, nearly 100%, in hardness compared to pristine SiOC glass sample. The size of the diamond particles has an influence on density and microstructure of the composites. The TEM investigations reveal that SiOC glass matrix and 2 μm diamond particles have excellent bonding. The present study demonstrates the possibility of fabricating bulk SiOC glass–diamond composites via the polymer-processing route, resulting in composites with promising mechanical properties.

Description: The internal flow characteristics of a kaolin suspension were examined via magnetic resonance imaging (MRI) in a flow regime for which the material behaves as an almost pure plastic material. The paste also showed a significant tendency toward liquid phase migration under squeezing tests. The MRI measurements produced a 2D slice of the 3D velocity field near the entrance of the cylindrical extrusion die, as well as the relative liquid–solid ratio within the cylindrical extrusion cartridge. Finite element simulations were also carried out using a simple yield stress fluid model, i.e. Herschel–Bulkley model, which was fit to rheometrical data obtained from independent experiments. A relatively good agreement between numerical simulations and the measured velocity field was obtained. In addition, the clay concentration of the paste within the extrusion column was imaged before and after extrusion experiments displaying a migration of water from the dead zones toward the entrance of the die. It is remarkable, however, that this phenomenon does not significantly affect the velocity distribution.

Description: The gradually varied air spheres radii and its controllable bandgap properties were studied in the three-dimensional inverse diamond structure ceramic photonic crystals (PCs). The PCs were fabricated by stereolithography and gel-casting process using alumina slurry. It was found that, as the radius increased, the bandgap width also increased and the center frequency of the bandgap shifted to the higher frequency range. These results agree well with the simulation results by Finite Integration Technique. Several PCs with gradually varied radii were combined together along the direction 〈100〉 to investigate their complex bandgap properties. Compared with the perfect PC, the bandgap width of the combined PCs increased remarkably with decrease ratio of radius increasing when the electromagnetic wave transmits along the direction in parallel to the combined direction of PCs. When the radius decreased to 20% of the perfect PC, the bandgap width reached 234% of that of the perfect PC. The resulting gap-midgap ratio is 46.2%. When the electromagnetic wave transmits along the direction in vertical to the combined direction of PCs, the bandgap width increased gradually, and that reached the maximum value when the decrease ratio was 20%.

Description: Diffusivity at 1130°C of Li + in LiNbO 3 crystal in off-congruent, Li -deficient regime has been studied as a function of Li 2 O -content. A diffusion-limited Li 2 O -content reduction depth profile in an X- or Z-cut plate, ranging from 47.2 to 48.5 mol%, was produced by carrying out Li -poor vapor transport equilibration (VTE) treatment on 1-mm-thick, initially congruent plates at 1130°C for 150 h. The profile was obtained by alternatively doing the optical polish to one crystal surface and the Li 2 O -content characterization on the polished surface through the measurement on birefringence. The Boltzmann–Matano mathematical analysis was applied to the profile to obtain the Li 2 O -content dependence of Li + diffusivity. The results show that the diffusivity decreases with the decreased Li 2 O -content and the decrease is by at least one order of magnitude as the Li 2 O -content decreases by 1 mol% from 48.5 mol%. The diffusion shows slight anisotropy and is faster along the optical axis direction of crystal. In combination with previously reported result in the near-stoichiometric regime, the diffusivity over the Li 2 O -content range from 47 to 50 mol% is presented.

Description: The Al 2 O 3 –ZrO 2 composite ceramics were prepared by slip casting in plaster molds and sintering at 1350°C in air. The composition of prepared samples varied from pure alumina to doped zirconia (3Y-TZP) with steps of 10 vol%. The relative density of the sintered samples varied from 94% to 98%, depending on the composition. Thermal diffusivity of sintered samples was measured by means of the xenon flash method at 100°C, 200°C, 400°C, 600°C, 800°C, and 1000°C and thermal conductivities were calculated based on measured bulk densities and specific heat data and finally corrected for porosity effects. As expected, the thermal conductivity decreased with increasing zirconia content, and in the case of samples with higher alumina content, it also decreased with increasing temperature. Effective thermal conductivities are close to the lower Hashin–Shtrikman bound and the recently proposed sigmoidal average. Empirical relations were used to fit the dependence of effective thermal conductivity of Al 2 O 3 –ZrO 2 composite ceramics on both composition and temperature.

Description: We present a general protocol for processing cost-beneficial, environmentally benign aqueous-type suspensions containing metal-oxide nanostructured particles, and their patterning with piezoelectric ink-jet printing technology. The critical issues relevant to ink-jet printing are the preparation and stabilization of nanosized particles in a fluid and adjusting its physical properties to the values appropriate for a particular ink-jet printer mechanism. We discuss and illustrate, on a model titania system, the processing of a highly stable, colloidal, water-based suspension containing particles not bigger than 570 nm, prepared by a ball-milling process. For the ink-jet printing experiments, the surface tension and the viscosity of the suspension were modified by the addition of a small amount of the appropriate non-ionic amphiphiles and glycerol. The formation of droplets, their positioning on the substrate, and the shape and uniformity of the dots on the substrate are discussed and correlated with the fluid properties via the inverse Ohnesorge number Z . It was shown successfully that uniform, regular-shaped TiO 2 dots with a diameter of 30 μm and a good positioning accuracy on Si/SiO 2 substrates could be obtained by jetting a fluid with Z values of 5 and 9 using a piezoelectric ink-jet printer with a nozzle diameter of 21 μm operating at an amplitude of 13 V and a frequency of 5 kHz.

Description: A new composition of phosphor material AlON:Er 3+ codoped with Mg 2+ were prepared by solid-state reaction method. The effect of Mg 2+ dopants on upconversion luminescence properties of the AlON:Er 3+ phosphor was investigated. At certain concentrations, Mg 2+ dopants were found to greatly enhance the red emission intensity of AlON:Er 3+ phosphors. From our results, the enhancement of the emission intensity by Mg 2+ dopants was discussed in terms of the Er 3+ distribution in crystal lattice and crystal symmetry by introducing oxygen vacancy.

Description: The lifetime of aluminum reduction cells is driven primarily by the lifetimes of two components of the cell lining: the carbon cathode and the sidewall refractory material. The current state-of-the-art sidewall material is a silicon nitride bonded silicon carbide (SNBSC) refractory and its corrosion mechanisms in the aluminum reduction cell environment have been examined in this study. Microstructural analysis of commercial SNBSC materials identified variations in porosity and α/β Si 3 N 4 ratio in the binder phase, with higher porosity levels and β Si 3 N 4 content found in the interior part of the block. Unreacted metallic silicon was observed only as a crystalline phase encapsulated inside SiC grains and not in the binder phase. The effects on the corrosion rate of porosity levels, amount of binder, α/β Si 3 N 4 ratio, and different factors in the environment, were examined in laboratory scale trials. High corrosion rates were associated with high porosity levels and a high β Si 3 N 4 fraction in the binder. The crystal morphology of β Si 3 N 4 is suggested as the main reason for the higher reactivity of this material. This morphology presents a higher surface area compared with α Si 3 N 4 crystals. A corrosion mechanism for SNBSC materials in the aluminum reduction cell atmosphere is suggested.

Description: A comprehensive review on the latest development of the antiferroelectric ↔ ferroelectric phase transition is presented. The abrupt volume expansion and sudden development of polarization at the phase transition has been extensively investigated in PbZrO 3 -based perovskite ceramics. New research developments in these compositions, including the incommensurate domain structure, the auxetic behavior under electric fields in the induced ferroelectric phase, the ferroelastic behavior of the multicell cubic phase, the impact of radial compression, the unexpected electric field-induced ferroelectric-to-antiferroelectric transition, and the phase transition mechanical toughening effect have been summarized. Due to their significance to lead-free piezoelectric ceramics, compounds with antiferroelectric phases, including NaNbO 3 , AgNbO 3 , and ( Bi 1/2 Na 1/2 ) TiO 3 , are also critically reviewed. Focus has been placed on the ( Bi 1/2 Na 1/2 ) TiO 3 – BaTiO 3 solid solution where the electric field-induced ferroelectric phase remains even after the applied field is removed at room temperature. Therefore, the electric field-induced antiferroelectric-to-ferroelectric phase transition is a key to the poling process to develop piezoelectricity in morphotropic phase boundary (MPB) compositions. The competing phase transition and domain switching processes in 0.93( Bi 1/2 Na 1/2 ) TiO 3 –0.07 BaTiO 3 are directly imaged with nanometer resolution using the unique in situ transmission electron microscopy (TEM) technique.

Description: Hollow Silica ( SiO 2 ) fibers with porous walls were synthesized by a coaxial electrospinning method. The SiO 2 sol prepared by a sol–gel route was blended with polyvinylacetate to prepare precursor solutions for electrospinning. Electrospinning-synthesized hollow SiO 2 fibers were highly porous with pore diameters of ~45 nm. A slow heating rate 〈5°C/min during calcination was required to sustain the hollow and porous morphology. In addition, aligned hollow SiO 2 fibers were successfully synthesized using a separate electrode configuration.

Description: Coarsening induced reverse phase transformation of hafnia in polymer-derived Si–Hf–C–N–O ceramics was studied experimentally. X-ray diffraction and high resolution transmission electron microscopy were used to obtain information regarding nanocrystalline structure. Hafnia crystallites precipitated out from the amorphous ceramic matrix on heat treatment were observed to remain as tetragonal hafnia below a critical crystallite radius of 4 nm. Prolonged heat treatment has resulted in coarsening, as explained by Lifshitz–Slyozov–Wagner model, resulting in reverse phase transformation from tetragonal to monoclinic hafnia.

Description: In this work, anisotropic LiNb 0.6 Ti 0.5 O 3 (LNT) template particles are prepared by molten salt synthesis in LiCl flux. Plate-like particles with diameters of 5–20 μm and thicknesses of 0.5–2.0 μm synthesized at 1000°C are chosen as templates. Highly textured microwave ceramics of M-phase LNT with tunable dielectric properties are fabricated by a novel screen-printing templated grain growth technique (sp-TGG), and their characteristics and dielectric properties are studied systematically. Dielectric anisotropy is observed in dielectric constant ( ε r ) and the temperature coefficient of dielectric constant ( τ ε ) at 1 MHz. LNT(//) samples exhibit lower ε r (=55.3) than randomly oriented ceramics and a positive temperature coefficient τ ε (75 ppm/°C), whereas, LNT(⊥) samples exhibit higher ε r (=83.6) and a negative temperature coefficient τ ε (= −120 ppm/°C). The textured ceramics also exhibit anisotropic and excellent properties at microwave frequency, with LNT-M(//) showing ε r  = 57.9, Q  ×  f =  6325 GHz, τ f   = −14 ppm/°C and LNT-M(⊥) showing ε r  = 81.8, Q  ×  f =  5751 GHz, τ f   = 43 ppm/°C. By tailoring along different directions, continuously tunable dielectric constant ranging from 55 to 83 could be obtained, and τ f could be changed from −14 to 43 ppm/°C. These findings can be technologically beneficial for wireless communication devices.

Description: This article examines carbothermal reduction/nitridation of rutile in a H 2 –N 2 gas mixture in the temperature-programmed and isothermal experiments in a fixed-bed reactor. The aim of this investigation was to establish the reduction/nitridation sequence, the reaction degree, and the rate of synthesis of titanium oxycarbonitride under different experimental conditions. The off-gas composition was monitored using an infrared sensor (CO, CO 2 , and CH 4 ) and a dew point analyzer (H 2 O). Extents of reduction and nitridation were determined from the off-gas composition and LECO analysis. Phase composition of reduced samples was analyzed using powder X-ray diffraction (XRD). Rate and extent of conversion of titanium oxides to titanium oxycarbonitride increased with increasing temperature. The conversion of titania into titanium oxycarbonitride at 1150°C was completed in 180 min; the conversion time decreased to 30 min at 1300°C. Increasing temperature resulted in formation of titanium oxycarbonitride with higher TiC content. Porosity had a minor effect on the reduction/nitridation of titania with the tendency to increase the reduction rate with increasing porosity. Reduction/nitridation of titania at 1150°C followed the sequence: TiO 2 →Ti 5 O 9 →Ti 4 O 7 →Ti 3 O 5 →TiO x C y N z .

Description: A unique configuration of PbZr 0.4 Ti 0.6 O 3 multilayer stack was designed and grown on F-doped tin oxide thin film by spin casting and annealing process. The multilayer system exhibits a broad reflection band with peak reflectivity over 95% and band width no 〈 40 nm, a dielectric constant of 520 and dielectric tunability of ~49% at 1 MHz, a remanent polarization of 46.8  μ C/cm 2 , and a polarization loss of 〈 5% after 10 9 polarization switching cycles, rendering excellent performance as 1D photonic crystals and as ferroelectric and dielectric media. This material structure may find application in photonic band-gap engineering, microwave tunable devices, and integrated optoelectronics.

Description: The Ce 3+ -doped Y 2 O 3 –Al 2 O 3 –SiO 2 (YAS) bulk glasses with low SiO 2 (≤40 mol%) were prepared by flame spray-quench method and hot press sintering. YAG nanoglass-ceramics were derived from YAS bulk glass by a controlled crystallization. The differential thermal analysis (DTA) results showed that the glass-forming ability of YAS system was strongly dependent on SiO 2 content and the supercooling degree required for forming YAS glass increased with the decrease of SiO 2 content. The YAS glass compositions had been extended to low SiO 2 phase region (10–40 mol%) by flame spray-quench method. The study of crystallization process showed that glass matrixes experienced initially a phase-separation followed by crystallization during the heat treatment. The phase-separated grains (100–300 nm) that were composed of YAG nanocrystallites precipitated in the glass matrix. And the intensity of emission spectra increased with the decreasing SiO 2 content.

Description: A new high-temperature ferroelectric ternary solid solution x Bi(Mg 1/2 Ti 1/2 )O 3 – y Bi(Zn 1/2 Ti 1/2 )O 3 – z PbTiO 3 has been developed and characterized. A detailed study on the preparation and characterization of the compositions along the pseudobinary line x PT-(1− x )(0.9BMT-0.1BZT) has been performed to study the property trends with composition. High c / a ratio of 1.04 has been observed for the composition with surprisingly low tolerance factor of 0.97. These compositions have been studied with focus mainly on the tetragonal phase field. Varied transition temperature trends have been observed along the pseudobinary line, which is then compared with the individual binary BZT-PT and BMT-PT systems. Structure property relationship is evaluated and discussed in terms of modern ferroelectric theories.

Description: Ferroelectric properties of Dy and Mn codoped BiFeO 3 , (Bi 1- x Dy x )(Fe 1- x Mn x )O 3 (BDFM- x , x  =   0, 0.02, 0.04, 0.06, 0.08, and 0.10), thin films were investigated. Improved ferroelectric properties were observed in the codoped thin film capacitors. Among them, BDFM-0.08 thin film capacitor exhibited the best properties. The remnant polarization (2 P r ) and coercive electric field (2 E c ) of the BDFM-0.08 thin film capacitor were 96 μC/cm 2 and 695 kV/cm at an applied electric field of 1061 kV/cm, respectively. The leakage current density of the BDFM-0.08 thin film capacitor was 8.3 × 10 −5  A/cm 2 at 400 kV/cm.

Description: Many techniques exist to synthesize zirconia and YTZP with a nano-scale particle size, but a recently developed hydrothermal precipitation procedure has shown promise in producing high-yield quantities of well-dispersed 8–10 nm zirconia and YTZP. Using bicine as a complexing agent, a homogeneous solution of zirconyl nitrate and yttrium nitrate is formed; after hydrothermal treatment, 8–10 nm tetragonal zirconia or YTZP particles are precipitated. With the modified hydrothermal procedure, powder yield was increased to 100 g of powder per liter of reactant solution without significantly changing the powder characteristics. X-ray diffraction and Raman spectroscopy were used to verify that the tetragonal phase was formed in the 1YTZP composition. Complementary particle size measurements were made using dynamic light scattering, BET nitrogen adsorption, and X-ray diffraction; differences in measured particle size are discussed, and all three techniques verify the 8–10 nm particle diameter. Particle morphology and impurity content were measured with transmission electron spectroscopy and X-ray fluorescence, respectively. To overcome the increased likelihood of agglomeration that accompanies the increased synthesis, wash solutions of deionized water, bicine, and oxalic acid were compared, and the particle–particle interactions of nano-YTZP in these wash solutions and in ethanol are modeled with modified DLVO theory. The results show that yttria leaching is prevented and dispersion is promoted by laundering with a solution of oxalic acid and dispersing into deionized water, both adjusted to a pH value of 9.

Description: An aqueous nitrate-based precursor solution was deposited on stainless steel substrate by spray pyrolysis to produce thick lanthanum zirconate coatings for thermal barrier coating application. The as-deposited, dried, and further annealed coatings were characterized by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The influence of the substrate temperature on the film formation and microstructure has been carefully studied for a better understanding of the deposition mechanisms. A temperature range corresponding to the deposition of an ionic salt liquid was found to be critical to obtain thick crack-free green coatings. Further heat treatment was necessary to decompose the nitrate species into an oxide coating with a fine porous microstructure.

Description: Phase pure calcium cobaltate ( Ca 1.24 Co 1.62 O 3.86 ) was prepared by Self-propagating High-temperature Synthesis (SHS) followed by a short post heat treatment. Prepared powders were characterized by XRD for phase purity, and SEM for particle size, and distribution. Temperature histories at the center and on the surface of reaction pellet during the SHS process were monitored and recorded. Particle size of synthesized powders was reduced using a planetary mill to increase its specific surface area. Electrical conductivity, thermal conductivity, and Seebeck coefficient of the prepared power were measured and figure of merit was reported.

Description: The influence of carbon impurities on phase composition, microstructure, and mechanical properties of hot-pressed ZrB 2 –SiC ceramics was studied. Carbon was either present in the starting ZrB 2 powders or introduced due to the carbon-rich sintering environment. Carbon present in the starting ZrB 2 powders removed the inherent oxygen impurities to enable ceramics that appeared phase pure by X-ray diffraction, had smaller average grain sizes, and had higher Vickers’ hardness, but lower fracture toughness. Carbon introduced from the sintering environment led to the formation of secondary ZrC , allowed the microstructure to coarsen, and decreased the fracture toughness. This study showed that ZrB 2 –SiC ceramics with refined microstructure could be obtained by introducing carbon impurities in the starting ZrB 2 powders, whereas the densification should be carried out at lower temperature to avoid the carbon uptake from sintering environment.

Description: Boron nitride nanotubes (BNNTs)/alumina composites were fabricated by hot pressing. The effect of BNNTs on the mechanical properties, including ambient and high-temperature flexure strength and fracture toughness was investigated. As a result of sufficient physical and chemical bonding between BNNTs and alumina, the pullout and fracture of BNNTs concurrent with the suppression of BNNTs on abnormal growth of grains contributes to the excellent ambient and high-temperature mechanical properties.

Description: Ho 31 and/or Yb 31 doped glass ceramics containing spherical BaF 2 nanocrystals sized 10–20 nm were prepared by melt quenching and subsequent thermal treatment. Radiative properties such as transition probabilities (A), radiative lifetimes (τ), branching ratios (β) along with absorption and emission cross sections have been calculated from the absorption spectra. Upon 637 nm excitation, Ho 31 -doped glass ceramics yield an intense infrared emission at 1191 nm with a full-width at half-maximum of 80 nm and weaker emissions at 980 and 1473 nm. Efficient 1.2 and 2.0 μm infrared emissions have been achieved in Ho 31 / Yb 31 co-doped glass ceramics under 980 nm excitation, demonstrating the occurrence of energy transfer (ET) from Yb 31 to Ho 31 . The microscopic parameters of the ET processes between Yb 31 and Ho 31 have been evaluated, revealing that the forward ET Yb 31 → Ho 31 is more efficient than the backward one and both the processes are mainly assisted by one-phonon emission (annihilation).

Description: Samples taken from the core of real-sized castable pieces were studied under TGA, DTA, SEM, and XRD techniques after hydration during normal dry-out process. The TGA was also performed at bulk samples, and the effect of volume on the hydration process was evaluated. The castables consisted of dead-burned magnesia with additions of calcined and/or tabular aluminas, or microsilica to the matrix. The addition of alumina in combination with magnesia increased the hydration rate during the drying of the castable due to a lower permeability of the casted piece. Addition of microsilica, on the other hand, reduced damage due to hydration. The microsilica promotes the formation of a low crystallinity chrysotile precursor, due to its reaction with the magnesium hydroxide formed after the hydration of the surface of magnesia grains. This phase alleviates the stress generally associated to hydroxide formation, which otherwise leads to structural spalling.

Description: Nb -doped 0.9 BaTiO 3 –0.1 Bi 0.5 Na 0.5 TiO 3 (0.9BT–0.1BNT) ceramics were prepared by conventional solid-state method. The dielectric and the structural properties were investigated. It was found that the temperature–capacitance characteristics greatly depended on Nb 2 O 5 content. With the addition of 2.0 mol% Nb 2 O 5 , 0.9BT–0.1BNT ceramic sample could satisfy the EIA X9R specification. This material was promising for high-temperature MLCC application. Microstructure element distribution was studied using TEM and EDS. The Bi and Na were almost homogeneously distributed except grain-boundary segregation of Bi . The Nb exhibited a nonuniform distribution from the grain boundary to the interior, showing the simultaneous presence of Nb -rich and Nb -poor regions. Such microheterogeneity gave rise to the temperature stability of permittivity. The solution-precipitation mechanism was introduced to elucidate the evolution of microstructures. Degradation and recovery of insulation resistance were observed under a dc bias at 200°C, which was attributed to the electromigration and diffusion of Na + .

Description: Three-dimensional (3-D) images of two ceramic-matrix textile composites were captured by X-ray micron-resolution computed tomography (μCT) on a synchrotron beamline. Compared to optical images of sections, CT data reveal comprehensive geometrical information about the fiber tows; information at smaller scales, on matrix voids, individual fibers, and fiber coatings, can also be extracted but image artifacts can compromise interpretation. A statistical analysis of the shape and positioning of the fiber tows in the 3-D woven architecture is performed, based on a decomposition of the spatial variations of any geometrical characteristic of the tows into non-stochastic periodic trends and non-periodic stochastic deviations. The periodic trends are compiled by exploiting the nominal translational invariance of the textile, a process that maximizes the information content of the relatively small specimens that can be imaged at high resolution. The stochastic deviations (or geometrical defects in the textile) are summarized in terms of the standard deviation of any characteristic at a single point along the axis of a tow and correlations between the values of deviations at two different points on the same or different tows. The tow characteristics analyzed consist of the coordinates of the centroids of a tow, together with the area, aspect ratio, and orientation of its cross-section. The tabulated statistics are sufficient to calibrate a probabilistic generator (detailed elsewhere) that can create virtual specimens of any size that are individually distinct but share the statistical characteristics of the small specimens analyzed by X-ray μCT. The data analysis presented herein forms the first step in formulating a virtual test of textile composites, by providing the statistical information required for realistic description of the textile reinforcement.

Description: Designing guidelines for glass-free low-temperature cofired ceramic (LTCC) materials were proposed from the point of view of crystal chemistry. As an example, Ca 1− x (Nd 0.5 Li 0.5 ) x WO 4 was successfully designed as glass-free LTCC materials by crystal chemistry. The sintering behavior, microstructure, and microwave dielectric properties of Ca 1− x (Nd 0.5 Li 0.5 ) x WO 4 ceramics were investigated in this study. The structure and microstructure of the compounds were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 9–13 GHz. Continuous solid solutions Ca 1− x (La 0.5 Na 0.5 ) x WO 4 (0.1 ≤  x ≤0.5) were formed as expected in the experimented composition range. They could be sintered into dense ceramics (approximately 96%–98% theoretical density) at 825°C–875°C per 2 h. All samples exhibit Scheelite structure (I4 1 /a) phase. Both of the sintering temperature and microwave dielectric properties, especially the temperature coefficient of resonant frequency ( τ f ), could be tuned in a wide range. Combined excellent microwave dielectric properties with ε r  = 11.7, Q × f  =   36 700 GHz, and τ f  = 5.36 ppm/°C could be obtained for the x  = 0.2 composition after sintering at 825°C/2 h. The chemical compatibility of Ca 0.8 (Nd 0.5 Li 0.5 ) 0.2 WO 4 ceramic with silver ( Ag ) powders was also investigated. No chemical reaction has taken place between the matrix phase and Ag after sintering at 850°C/2 h. Thus, it can be used as a promising glass-free microwave dielectric material for LTCC applications.

Description: Grain growth in 8 mol% Y 2 O 3 -stabilized zirconia ceramics (8YSZ) under an electric current has been investigated. Enhanced grain growth on the cathode side starts at 1150°C, well below the conventional sintering temperature, while grain growth is dormant on the anode side until 1400°C. In fully dense samples, the grain size undergoes an abrupt transition, differing by a factor of more than 10 on the two sides. Porous samples also experience faster densification on the cathode side, but grain growth is postponed until full density is first reached. Estimated grain boundary diffusivity on the cathode side has an apparent activation energy about 1 eV lower than that of normal grain boundary diffusion. These results are attributed to supersaturated oxygen vacancies accumulated on the cathode side, causing cation reduction that lowers their migration barrier.

Description: Solid solution magnesium aluminate spinel with the alumina-rich composition MgO ·1.2 Al 2 O 3 has been prepared as a transparent polycrystalline ceramic with average in-line transmission at 550 nm of 84.8 ± 2.7% and 〉82% throughout the visible spectrum. Starting powders are prepared from mixtures of high purity Mg(OH) 2 and γ-Al 2 O 3 thoroughly mixed in an aqueous slurry. Water is removed by rotary evaporation. The solids are collected, dried, calcined, mixed with LiF (as a sintering aid), and sieved. The powders are sintered into dense ceramics by hot pressing at 1600°C under vacuum and 20 MPa uniaxial load followed by hot isostatic pressing at 1850°C under 200 MPa Ar . Final grain sizes ranged between 300 and 1000 μm. Samples exhibited flexural strength of 176.8 ± 46.2 MPa; hardness of 12.3 ± 0.2 GPa; and elastic modulus of 292.9 ± 7.5 GPa. Control samples of stoichiometric magnesium aluminate spinel ( MgO · Al 2 O 3 ) were prepared with the same procedure and exhibited comparable values for transmission and physical properties.

Description: A new pyrochlore homogeneity field in Bi 2 O 3 –Fe 2 O 3 –TeO 3 system is characterized with respect to its compositional range and phase relations to adjacent phases. The sintering temperature of these pyrochlores is 880°C and they do not react with metallic silver, which makes them suitable for low-temperature cofired ceramics (LTCC) technology. Magnetic measurements indicate a spin-glass formation. The spin freezing temperature that occurs at around 20 K shows a slight, yet systematic, variation with the sample composition. The dielectric constant increases with an increase in Bi content from 37(1) to 55(1). At cryogenic temperatures, they show the dielectric relaxation typical for displacive pyrochlores. The UV–Vis diffuse reflectance data were used for calculation of the electronic band gap. The lowest band gap was determined to be 1.965 eV. Next to the pyrochlore range, another new phase was discovered. Structural analysis showed that Bi 3 (Fe 0.56 Te 0.44 ) 3 O 11 crystallizes as KSbO 3 -type in a displacive disordered cubic symmetry with a lattice parameter of 9.47045(15) Å.

Description: Transparent yttria was prepared by means of high-pressure spark plasma sintering at 1050°C under the uniaxial pressure of 300 MPa. The resulting yttria possessed the in-line transmittance of 68% at the wavelength of 700 nm and the nanometric grains of about 400 nm. In the near-infrared spectral region, the transparency of the present specimen approached the level of single crystal yttria. This research highlighted the efficiency and simplicity of high-pressure spark plasma sintering for fabricating transparent yttria.

Description: Nanocomposite powders with equal volume fractions of Y 2 O 3 and MgO have been produced by the thermal decomposition of precursor mixtures of yttrium nitrate and magnesium nitrate. Solutions of the precursor salts were mixed with ammonium acetate fuel, dried to form a gel-like substance, and then calcined to give nanocrystalline ceramic powders. The amount of ammonium acetate added to the metal nitrate precursors was varied systematically, and the morphology and distribution of the component phases in consolidated compacts of the resultant ceramic powders were examined by a combination of focused ion beam sectioning, scanning, and transmission electron microscopy. The dispersion of the Y 2 O 3 and MgO phases within the synthesized powders improved, and the sizes of the phase domains reduced, with increasing ammonium acetate content up to the quantity required for a stoichiometric redox reaction with the metal nitrates. The addition of excess ammonium acetate gave no further improvement in phase domain dispersion or reduction in phase domain sizes. These phenomena are related to the thermal characteristics for the decomposition of the precursors and their effect on phase separation during oxide crystallization.

Description: The Japan Atomic Energy Agency (JAEA) has started to study and develop zirconium carbide ( ZrC )-coated fuel particles for advanced high-temperature gas-cooled reactors. The ZrC -coated particles have been fabricated at JAEA and then heat-treated to investigate the effects of the fuel compact sintering process. Remarkable ZrC crystal grain growth occurred in one batch, but not in another, in spite of both having the same C / Zr ratio and ZrC density. TEM/STEM observation of the specimens before heat treatment clarified that considerably more free carbons or voids, which would be expected to hinder the grain growth of ZrC with heat treatment, were distributed in the ZrC layer in the batch in which the remarkable ZrC crystal grain growth did not occur than in the other batch. Differences between these batches, which could not be detected by estimating the C / Zr ratio or the ZrC density, could be detected with positron annihilation spectroscopy (PAS). This result indicates that there is a possibility that PAS can be applied for quality control for ZrC -coated fuel particles in the future, as preparing specimens for PAS is much easier than for TEM/STEM observation. Moreover, PAS is much more suitable than microstructural observation for quantitative estimation. Characterization of defects detected with PAS would be the next step in this process for the investigation of the feasibility of the application of PAS to the quality control of ZrC -coated fuel particles.

Description: A new low-loss, low-temperature sinterable microwave dielectric material ZnTiNbTaO 8 was investigated for the first time. Single phase ZnTiNbTaO 8 was obtained by the conventional solid-state route and sintered at 1120°C – 1200°C for 6 h. Theoretical density, packing fraction, bond valence, and oxygen octahedron distortion were calculated. The excellent microwave dielectric properties of ε = 36.3, Qf  = 67 000 GHz, τ f   = − 57.66 × 10 −6 /°C were obtained from the new ZnTiNbTaO 8 materials sintered at 1140°C for 6 h.

Description: The development of p -channel tin oxide thin-film-transistors spurred the research into microstructural analysis of tin oxide phases and control of conduction type, as it is widely known that tin oxide thin films exhibit both n - and p -type conduction depending on growth conditions. This study reports the relationship between the microstructural properties and the ambiguity of the electrical conduction type observed in nonstoichiometric tin oxides. Nonstoichiometric tin oxide thin films have been produced by RF magnetron sputtering with a dependence on the growth gas atmosphere. The crystal phase of the tin oxide deposited under low ambient oxygen content was mainly SnO 1+ x with relatively stable p -type conduction. On the other hand, for deposition under high ambient oxygen content, phase separation with structural modulation in the tin oxide film occurred in SnO -like and SnO 2 -like regions. These phases with different conduction types caused electrically unstable dual conduction types in the tin oxide films, despite their low electrical resistivity.

Description: Although BaZr 0.8 Y 0.2 O 3−δ (BZY) possesses large bulk proton conductivity and excellent chemical stability, its poor sinterability and grain boundaries block proton conduction. In this work, the effect of Ca as a co-dopant and as a sintering aid (as CaO ), on the sinterability, proton conductivity, and fuel cell performance of BZY was investigated. The addition of 4 mol% CaO significantly improved the BZY sinterability: BZY pellets with densities of 92.7% and 97.5% with respect to the theoretical density were obtained after sintering at 1500°C and 1600°C, respectively. The improved BZY sinterability by CaO addition resulted also in a large proton conductivity; at 600°C, the total conductivity of BZY– CaO was 2.14 × 10 −3  S/cm, in wet Ar . Anode-supported fuel cells with 25 μm-thick BZY– CaO electrolyte membranes were fabricated by a dual-layer co-firing technique. The peak power density of the fuel cell with a BZY– Ni /BZY–4 CaO /BZY–LSCF ( La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3−δ ) configuration was 141 mW/cm 2 at 700°C, several times larger than the reported values of BZY electrolyte membrane fuel cells sintered with the addition of CuO or ZnO , demonstrating promising features for practical fuel cell applications.

Description: Lead-free ( Ba 1− x Ca x )( Ti 0.96 Sn 0.04 ) O 3 (BCST) ( x  =   0–0.04) ceramics were prepared using solid-state reaction technique. At room temperature, a polymorphic phase transition from orthorhombic phase to tetragonal phase was identified in the composition range of 0.01 ≤  x  ≤   0.03. Extremely high piezoelectric coefficient of d 33  = 510 pC/N and high planar electromechanical coupling factor of k p  = 48% were obtained for the BCST ceramics at x  =   0.02. These results indicate that the BCSTs are promising candidates for the widely used lead-based piezoelectric materials.

Description: Response to irradiation of nanocrystalline 3C–SiC is studied using 2 MeV Au 2+ ions at elevated temperatures and is compared to the behavior of its monocrystalline counterpart under the identical irradiation conditions. The irradiated samples are characterized using in-situ ion channeling, ex-situ X-ray diffraction, and helium ion microscopy. Compared to monocrystalline 3C–SiC , a faster amorphization process in the nanocrystalline material (average grain size = 3.3 nm) is observed at 500 K. However, the nanograin grows with increasing ion fluence at 550 K and the grain size tends to saturate at high fluences. The striking contrast demonstrates a sharp transition from irradiation-induced interface-driven amorphization at 500 K to crystallization at 550 K. The results could potentially have a positive impact on nuclear fuel cladding and structural components of next-generation nuclear energy systems.

Description: Transparent LaGdHf 2 O 7 ceramic was successfully prepared by reactive sintering using vacuum sintering at 1900°C for 6 h. The resultant ceramic has an in-line transmittance of 74% at 1100 nm and the density was measured to be 8.37 g/cm 3 . The average grain size was about 10 μm with uniform structure.

Description: In this work, the nonisothermal sintering behavior of as-received commercial high purity ZnO micrometric (m_ ZnO ), submicrometric (sm_ ZnO ) and nanometric (n_ ZnO ) powders was studied. The sintering behavior for sputtering target production was evaluated by changing the green density of samples from 62% of theoretical density (TD) to 35%. We observed that for n_ ZnO powder, the maximum shrinkage rate (MSR) temperature ( T MSR ) was not affected by the green density, and that it was reached at lower temperatures (~710°C) compared with m_ ZnO and sm_ ZnO powders. For these powders, the temperature of MSR increased from 803°C to 934°C and from 719°C to 803°C as TD changed from 62% to 35% TD, respectively. Small grain size (~0.560 μm) and high density targets were obtained for n_ ZnO when sintered at temperatures below the T MSR . Heating rate from 1°C to 15°C/min led to lower activation energy for n_ ZnO (~201 ± 3 kJ/mol) than for the submicrometric (sm_ ZnO ) (~332 ± 20 kJ/mol) and micrometric (m_ ZnO ) (~273 ± 9 kJ/mol) powders. Using the model proposed by Bannister and Woolfrey, an n value of 0.75 was found, which was correlated with a combination of viscous flow and volume diffusion mechanisms that should control the initial stage of n_ ZnO sintering. No significant differences were observed for n_ ZnO powder in terms of density when the size of targets (scale-up effect) was increased, while in the case of m_ ZnO and sm_ ZnO , a delay in the densification was observed, which was related to the higher sinterability of n_ ZnO powder. Two inches ZnO ceramic targets with different particle sizes and final densities were used in an rf magnetron sputtering system to produce ZnO films under the same deposition conditions. Films with thickness around 100 nm and good uniformity were produced using those targets, and no variation was observed in the optical and morphological properties. However, low electrical resistivity (1.4 Ω·cm) films were obtained with n_ ZnO targets, which could be explained in terms of a nonstoichiometric Zn:O composition of the started powders.

Description: It is well known that the piezoelectric properties of a thin film can be influenced by crystallographic texture. At the extreme case, epitaxial thin films can be deposited on single crystal substrates (with appropriate lattice matching) to effectively achieve a single crystal thin film. Here, the maximum advantage of orientation dependence is found. Typically this has required small, expensive single crystalline substrates. In the past 10 years, however, the technique of ion beam assisted deposition has been developed for applying a biaxially textured template to an arbitrary smooth surface. This has opened up a new realm of materials integration possibilities, with the prime example being high-temperature superconducting wires. Here, the same template is utilized for deposition of epitaxial Pb(Zr,Ti)O 3 thin films onto LaNiO 3 and La 0.7 Sr 0.3 MnO 3 -coated flexible substrates. Chemical solution deposition (CSD) is used to produce PZT thin films with very high (00 l ) orientation and excellent in-plane orientation. Macroscopic ferroelectric measurements depict very square hysteresis behavior, with high remnant polarization of ~40 μC/cm 2 . Piezoresponse force microscopy and local hysteresis measurements were used to image the microscopic domain structure and to demonstrate the piezoelectric behavior in these materials.

Description: An analytical procedure is developed which provides the magnitudes of the space charge potential and the corresponding grain boundary energy in ionic oxides from the effect of an applied dc electric field on grain growth. Reasonable agreement occurred between the calculated values and expectations or other measurements. The agreement indicates that the physical mechanism governing the retardation of grain growth by an electric field in 3Y-TZP is through reduction in the grain boundary energy by the interaction of the field with the space charge.