ALBERT

Description: Using a convenient solid-state reaction Ce 0.67 Tb 0.33 Mg 1- x Mn x Al 11 O 19 green phosphors were prepared. The effect of Mn 2+ doping on the luminescence properties, energy transfer mechanism, and color gamut under 254 nm excitation were investigated. The energy transfer from (Ce,Tb) 3+ to Mn 2+ was found to be due to multipolar interactions of the dipole–quadrupole mechanism from theoretical fitting results. The critical distance was calculated to be 0.797 nm. When the Mn 2+ doping content was increased from 0 to 0.12, the energy transfer efficiency (Ce 3+ ,Tb 3+  → Mn 2+ ) gradually increased from 0% to 58%. The Ce 0.67 Tb 0.33 Mg 0.88 Mn 0.12 Al 11 O 19 sample exhibits 105% of the standard NTSC color gamut. Results indicate that Ce 0.67 Tb 0.33 Mg 0.88 Mn 0.12 Al 11 O 19 green phosphors can be applied to illumination devices and displays.

Description: Highly infrared transparent tetragonal ZrO 2 (3 mol% yttria-stabilized) was prepared by means of high-pressure spark plasma sintering (HP-SPS). The crystallite size of the resulting dense sample was about 80 nm. In-line transmittance for the 1.5 mm thick sample ranged between 63% and 67% in the wavelength of 3–5 μm, representing 81%–87% of the theoretic value. Meanwhile, the cutoff wavelength of tetragonal ZrO 2 was superior to the values of other high-strength transparent ceramics. This study highlighted the efficiency and simplicity of HP-SPS for obtaining transparent tetragonal ZrO 2 and the great potential of this ceramic applied for durable infrared windows.

Description: We propose a simple and environmentally friendly method to prepare uniform-sized spherical ceramic foams (SCFs) with excellent pore properties by combining a drop-in-oil method with agar gelation. In addition, the change in size distribution and uniformity (characterized as coefficient of variation (C.V.)) and the corresponding pore-related properties for the SCFs were systematically investigated as functions of agar concentration (i.e., 0.50–1.50 wt% with respect to dry alumina). The results showed that uniform-sized SCFs were successfully fabricated regardless of agar concentration, that pore-related properties were gradually improved by increasing the agar content, and that the most uniform-sized SCFs were obtained when the agar concentration was 1.00 wt%. The extent of the improvement in size uniformity was evaluated by comparing the C.V. value for the drop-in-oil method with that for the pseudo-double-emulsion (PDE) method, which is an alternative method to fabricate SCFs. The C.V. values for the SCFs prepared by the drop-in-oil and the PDE method were determined to be 7% and 31%, respectively. The results clearly indicate that the size uniformity of the SCFs has been much improved for the drop-in-oil method as compared to the PDE method.

Description: Nanostructures of crystalline orthorhombic sodium niobate (NaNbO 3 ) were synthesized by a molten salt synthesis procedure. As a comparison, an auxiliary experiment via conventional solid state reaction process was carried out simultaneously. The microstructure and morphology evolution of the synthesized nano particles were investigated in detail, and on the basis of the experimental results, an in situ transformation mechanism has been proposed to elucidate the formation processes of NaNbO 3 microstructures. It was found that both the initial shape of the Nb 2 O 5 and the dissolution rate of the initial precursors critically determine the final shapes of the products. Furthermore, the determined electrical properties of the as-obtained products indicated that NaNbO 3 ceramic derived from nanostructures holds the real characteristic of ferroelectric and the polarization–electric field ( P–E ) hysteresis behavior is greatly influenced by the polarization treatment. The obtained NaNbO 3 ceramic after the polarizing treatment exhibited piezoelectric property, d 33  = 28 pC/N.

Description: Yttrium tetraboride was synthesized by reactions of Y 2 O 3 with B 4 C or with a B 4 C/C mixture. Fully dense YB 4 ceramics were prepared by hot-pressing at 1800°C and 20 MPa in He. The flexural strength and microhardness of the YB 4 were about 300 MPa and 27 GPa, respectively. Pure YB 4 showed considerable oxidation above 1200°C. The effect of SiC, AlN, and AlN/SiC on the properties of YB 4 ceramics was characterized. No chemical interactions were identified in the YB 4 –SiC and YB 4 –AlN pseudo binaries. The addition of SiC improved the oxidation resistance below 1200°C. At higher temperatures, the low viscosity of a surface melt caused its continuous runoff and the loss of the oxidation-protection capability of the scale. The addition of AlN/SiC improved the oxidation resistance compared to the ceramics containing only SiC, which was attributed to the presence of Al 2 O 3 in the Y 2 O 3 –SiO 2 –B 2 O 3 glass leading to an increase in its viscosity and preventing glass runoff. A significant improvement in the oxidation resistance of the YB 4 ceramics and extension of their oxidation stability to 1400°C was accomplished by the introduction of AlN only.

Description: The energy transfer from Tb 3+ to Eu 3+ -doped SiO 2 (SiO 2 :Eu 3+ , Tb 3+ ) inverse opal photonic crystals was investigated by photoluminescence and fluorescence lifetime. The results showed that the photonic band gap enhanced energy transfer from the donor Tb 3+ to the acceptor Eu 3+ . When the fluorescence emission wavelength of Tb 3+ overlaps the photonic band gap, the fluorescence intensity of Tb 3+ is suppressed, and the fluorescence intensity of Eu 3+ is increased because of the enhancement of energy transfer. In addition, the fluorescence lifetime of Tb 3+ decreased.

Description: Three-dimensional electron backscatter diffraction was used to measure the crystallographic distribution of the electrochemically relevant triple phase boundary lines and surfaces near them in SOFC cathodes made up of a porous mixture of yttria-stabilized zirconia and lanthanum strontium manganese oxide, both before and after mild electrochemical loading. All distributions were observed to be nearly isotropic, but non-random textures above the detection threshold were observed. The distributions differ between the two cells, as do the phase fractions and the electrochemical history. The different distributions are interpreted as evidence that steady-state distributions vary locally with phase fractions or that they evolve during the initial operation of the fuel cell. The rates at which triple lines, pore surfaces, and interface boundaries in the porous mixture approach a steady-state value appear to decrease with the average amount of mass transport required to reorient that specific feature. This work provides initial insights into the crystallography of interfaces in a multiphase ceramic material.

Description: Pb x Sr 1-x TiO 3 (PST) thin films with the ratio Pb/Sr = 40/60 were deposited on silicon substrate with Pt or LaNiO 3 (LNO) bottom electrodes by radio frequency magnetron sputtering followed by a postannealing treatment. The structural and microstructural analyses were performed and a perovskite phase was obtained whatever the nature of the bottom electrodes and even at a low temperature (450°C). The optimal annealing temperature is 650°C at which the films have a dense and fine microstructure. For electrical characterization the different top electrodes (Pt and LNO) were used. In both cases, we demonstrate that PST films present excellent performances in terms of dielectric properties and in particular, the tunability and Figure of Merit. A large tunability (57% at 400 kV/cm) and low dielectric losses (1.4%) were measured at 10 kHz for Pt/PST/Pt structures postannealed at 500°C. For LNO/PST/LNO structures, postannealed at 650°C, the improved tunability (≈80%) and low loss factor (≈2%) were obtained. Prospects of PST as an alternative to BST for tunable applications with a real potentiality of monolithic integration with silicon, in terms of thermal budget, are considered.

Description: The 2.7 μm emission has been obtained using 980 nm laser excitation in Er 3+ /Tm 3+ /Pr 3+ triply doped ZrF 4 –BaF 2 –LaF 3 –AlF 3 –YF 3 glass. 2.7 μm emission characteristics and energy transfer are investigated. Population inversion between the 4 I 11/2 and 4 I 13/2 levels is significantly enhanced by way of Tm 3+ and Pr 3+ co-doping into Er 3+ -doped fluoride glass. These results indicate that this Er 3+ /Tm 3+ /Pr 3+ triply doped fluoride glass has potential applications in 2.7 μm laser.

Description: The changes in the ferroelectric and magnetic properties of the nanostructured Pb(Zr 0.52 Ti 0.48 ) 1-x Fe x O 3 (0 ≤ x ≤ 0.06) due to the doping of different amounts of acceptor ions (Fe 3+ ) have been studied. X-ray diffraction studies show that the system maintains the tetragonal phase up to the doping of 2 mol% of Fe 3+ and the formation of secondary phase magnetoplumbite (PbFe 12 O 19 ) on further doping. Electron paramagnetic resonance studies have revealed the formation of defect centers which in turn arise due to the interaction of Fe 3+ ions with oxygen vacancies, which are generated in the lattice. This results in the appearance of room temperature ferromagnetic (RTFM) behavior in the doped samples. The dielectric studies reveal that with the concentration of Fe 3+ the peak near the maxima of dielectric constant (ε′ m ) is broadened. Studies of the defect dipoles on the ferroelectric properties have been performed by polarization measurement. The variations of the above properties with the structural and morphological features of the samples have also discussed.

Description: We combine chelate-assisted solvent extraction (CASE) and hot hydrogen fluoride gas treatment to enable a general method for the preparation of high-purity binary metal fluorides. The fluorozirconate glass ZBLANI:Yb 3+ (ZrF 4 –BaF 2 –LaF 3 –AlF 3 –NaF–InF 3 –YbF 3 ), a solid-state laser-cooling material, is used as a test case to quantitatively assess the effectiveness of the purification method. The reduction of transition-metal and oxygen-based impurities is quantified directly by inductively coupled plasma mass spectrometry (ICP-MS) and indirectly by laser-induced cooling, respectively. The concentrations of Cu, Fe, Co, Ni, V, Cr, Mn, and Zn impurities in the ZrCl 2 O precursor solution were measured individually by ICP-MS at various stages of the purification process. CASE was found to reduce the total transition-metal concentration from 72500 to ~100 ppb. Laser cooling was most efficient in ZBLANI:Yb 3+ glass fabricated from CASE-purified metal fluoride precursors, confirming the results of the ICP-MS analysis and demonstrating the effectiveness of the purification methods in a finished optical material. High-purity metal fluorides prepared by the methods presented herein will enable new high-performance optical materials for solid-state optical refrigerators, crystals for vacuum ultraviolet (VUV) spectroscopy of the Thorium-229 nucleus, VUV optics, fibers, and thin-film coatings.

Description: The oxidation and scale crystallization kinetics of Hi-Nicalon TM -S SiC fibers were measured after oxidation in dry air between 700° and 1400°C. Scale thickness, composition, and crystallization were characterized by TEM with EDS, supplemented by SEM and optical microscopy. TEM was used to distinguish oxidation kinetics of amorphous and crystalline scales. Oxidation initially produces an amorphous silica scale that incorporates some carbon. Growth kinetics of the amorphous scale was analyzed using the flat-plate Deal-Grove model. The activation energy for parabolic oxidation was 248 kJ/mol. The scales crystallized to tridymite and cristobalite, starting at 1000°C in under 100 h and 1300°C in under 1 h. Crystallization kinetics had activation energy of 514 kJ/mol with a time growth exponent of 1.5. Crystalline silica nucleated at the scale surface, with more rapid growth parallel to the surface. Crystalline scales cracked from thermal residual stress and phase transformations during cool-down, and during oxidation from tensile hoop growth stress. High growth shear stress was inferred to cause intense dislocation plasticity near the crystalline SiO 2 –SiC interphase. Crystalline scales were thinner than amorphous scales, except where growth cracks allowed much more rapid oxidation.

Description: The phase transitions in unpoled lead-free (1− x )(Bi 1/2 Na 1/2 )TiO 3 – x BaTiO 3 ( x = 0.06 and 0.11) ceramics are investigated using hot-stage transmission electron microscopy (TEM). It is found that large ferroelectric domains in both ceramics start to disappear around T d , the depolarization temperature. After the transition, both compositions exhibit the P 4 bm tetragonal symmetry in the form of nanodomains. The structural transition observed by the in situ TEM experiments seems to be gradual and occurs within a temperature range of several tens of degrees, in contrast to the sharp anomaly at T d revealed by the dielectric characterization. With further increasing temperature, no structural change was observed for both compositions across T RE , where the dielectric frequency dispersion vanishes, and T m , where the dielectric permittivity reaches maximum. The tetragonal-to-cubic transition is diffuse and takes place in a broad temperature window well above both T RE and T m . These results of structural phase transitions are summarized in a phase diagram with its composition range covering the morphotropic phase boundary (MPB).

Description: Zinc-blende-type cubic InSe and β-In 2 Se 3 crystallites were synthesized using the solvo-thermal method in this study. The crystalline structure, electronic and optical characterization of indium selenide particles were investigated using transmission electron microscopy (TEM), X-ray diffractometer (XRD), UV–visible absorbance spectra. It was observed that the dominant crystalline structure of samples synthesized at 180°C for 1.5–48 h is zinc-blende-type cubic InSe phase with lattice parameter of about 0.573 nm. As the reaction temperature was raised to 200°C, the zinc-blende-type cubic InSe phase diminished and the β-In 2 Se 3 phase was produced. The zinc-blende-type cubic InSe phase band gap is about 1.68 eV. These synthesized compounds provide promising candidates for solar cell applications.

Description: Upconversion emission of Yb, Er co-doped Bi 4 Ti 3 O 12 (Bi 4 Ti 3 O 12 : Yb, Er) inverse opal photonic crystals was investigated. Strong green (548 nm) and red (660 nm) upconversion emission bands were observed under a 980 nm excitation at room temperature. The results showed that the intensity of upconversion emission bands can be tuned by controlling the structure of the inverse opal. Significant suppression of the green or red upconversion emission was obtained if the photonic band gap overlaps with the Er 3+ ions emission band, resulting in color tunable up-conversion photonic crystals with applications in solid-state color displays.

Description: This article describes a study involving three-dimensional FIB tomographic characterization of Vickers microindentation sites in an alumina material containing pores. The study was carried out using a dual beam FIB instrument for loads in the range 50–200 g. The results obtained show that this technique can be used to obtain 3-D distributions of indentation-generated cracks. Although, compared to a dense material, presence of pores in alumina reduced the ability to generate and/or propagate radial cracks, the significant probability of crack-pore interactions indicates that pores assist in the generation/propagation lateral cracks. The subsurface images show that pores act as sites for crack initiation and/or assist in crack propagation. In addition, a clearly reduced ability to generate and/or propagate radial cracks has been noted. However, considering that FIB tomography is destructive and invasive, microstructural changes seem to have occurred during the process and consequently it is not possible to identify all the generated cracks. Moreover, propagation of some of the cracks also occurred due to material removal in FIB milling.

Description: Mesosporous carbon-bonded titanium-carbide/silicon-carbide (C-TiC/SiC) ceramics with a high specific surface area (221 m 2 /g), ultra fine grains (10–50 nm), and high crystallinity were synthesized from direct carbothermal reduction (1100°–1450°C) of monolithic Ti–Si–O–C precursors made from controlled sol–gel process. The nano-sized carbide grains are bonded into bulk materials by poly(furfuryl alcohol) (PFA) derived nanocrystalline carbon framework by “bridge,” “entanglement,” and “adhesive” effects. Graphenes were found to grow on {111} planes of TiC grains but this was not observed for SiC. The bonding of graphitic carbon layers on carbide grains support the nanostructure and also result in the desired combination of functional and mechanical properties.

Description: Infrared radiative properties of 8-mol%-yttria-stabilized zirconia (8YSZ) ceramics of porosity 3% as applied as electrolyte for solid oxide fuel cells (SOFCs) were studied at room and elevated temperatures in the wavelength range from 2 to 20 μm. The room-temperature directional-hemispherical measurements of reflectance and transmittance for thin samples were combined with normal emittance measurements at several temperatures up to 1700 K. The use of the radiation transfer theory in a region of semi-transparency enabled identification of absorption and scattering properties of the material. Both a detailed numerical procedure using the known discrete ordinates method and a novel iterative analytical solution were employed. An analysis based on the Mie theory confirms volumetric scattering by sub-micron size polydisperse pores in the ceramics. It is shown that the absorption coefficient of 8YSZ increases considerably with temperature. This effect should be taken into account in combined heat transfer calculations for SOFCs.

Description: A Ba 0.75 Sr 0.25 Ti 0.95 Zr 0.05 O 3 ceramic was developed for use in nonlinear transmission line (NLTL) applications. The sol–gel process was used to synthesize Ba 0.75 Sr 0.25 Ti 0.95 Zr 0.05 O 3 nanoparticles to achieve a uniform composition and a high surface area. Simultaneous thermal gravimetric analysis and differential thermal analysis (TGA/DTA) was used to identify the decomposition sequence as a function of temperature for the as-synthesized powders. The phase transformation was confirmed by X-ray diffraction (XRD). The calcined nanoparticles were hot-pressed at 1300°C to achieve a high density. Microstructures were characterized using scanning electron microscopy (SEM). Several dielectric properties were measured and are reported.

Description: Highly porous ceramics are critical components of Solid Oxide Fuel Cells. Nevertheless, their mechanical properties are poor and not fully understood. Herein, Discrete Element simulations are used to quantitatively assess the relation between the particulate microstructure of highly porous ceramics and their mechanical properties. Partially sintered ceramics are numerically generated with complex microstructures including pore formers and bilayers. These microstructures are then tested in tension and compression to obtain their elastic and fracture behavior. Compiling experimental data from the literature and simulations results, an Orowan–Petch type relation between strength and particle size is proposed for highly porous ceramics. It is based on the local fracture model at the length scale of solid bonds between sintered particles.

Description: We have studied the synthesis and near-infrared luminescent properties of Ni 2+ -doped ZnO–Al 2 O 3 –SiO 2 nanocomposite glasses embedded activated spinel nanocrystals prepared using a sol–gel technique. Nanocrystal-dependent optical properties in Ni 2+ -doped nanocomposite glasses were systematically investigated. We found that Ni 2+ ion is optically active only in the composite embedded nanocrystals, which can provide octahedral position with appropriate crystal field strength. Near-infrared emission ranging from 1100 to 1600 nm was observed in the Ni 2+ -doped composite fabricated by sol–gel method. Such an ultra-broadband luminescence from the nanocomposite could cover the infrared emission bands obtained from multiple rare earth ions (Ho 3+ , Pr 3+ , and Tm 3+ ) doped glasses.

Description: The (1- x - y )K 0.5 Na 0.5 NbO 3 - x CaZrO 3 - y LiNbO 3 (KNLNCZ- x - y ) lead-free piezoelectric ceramics were fabricated by conventional technique, and the effect of the addition of CaZrO 3 and LiNbO 3 on the phase transitions and piezoelectric properties of the KNN-based ceramics was investigated. The addition of CaZrO 3 will shift the orthorhombic-rhombohedral transition temperature of the ceramics to above room temperature, and with the increase of the CaZrO 3 additives, a dielectric peak rises up near the orthorhombic-tetragonal phase transition of the ceramics resulting in the spread of the ferroelectric-paraelectric phase transition over a rather wide temperature range due to polar nanoregions arising from composition fluctuation. For x = 0.05, the addition of LiNbO 3 is effective to shift the T R-O and T O-T downward and T C upward in KNLNCZ-0.05- y ceramics. Optimum piezoelectric properties ( d 33 = 216 pC/N and k p = 42.9%) were obtained for the KNLNCZ- x - y ceramics with x = 0.05 and y = 0.07 due to the decrease of T O-T to be around room temperature.

Description: Alumina-matrix composite containing 2.0 wt% boron nitride nanotubes and monolithic alumina were fabricated by hot pressing, and their thermal and mechanical properties were investigated. Thermal shock resistance was evaluated by water quenching and subsequently by measuring the residual flexural strength by three-point bending test. Though the residual flexural strength of the composite is higher than that of the monolith at temperature differences lower than 280°C, the thermal shock of the composite is more sensitive to temperature change, exhibiting no significant improvement in thermal shock resistance. The variation in thermal shock resistance for the composite is resulted from the introduction of BNNTs.

Description: Bulk 0.7PbZr 0.52 Ti 0.48 O 3 –0.3NiFe 2 O 4 nanoceramic composites with a grain size of ~50 nm were fabricated using chemical synthesis, high-energy ball-milling, and spark plasma sintering. The composite produced broad dielectric constant peaks and frequency dispersion, similar to relaxor ferroelectrics, and was ferroelectric and ferromagnetic. The dielectric and piezoelectric properties of nanoceramics are lower than those of microceramics due to grain-size effects. “Butterfly”-type magnetoelectric (ME) loops indicate that direct stress coupling between magnetostrictive and piezoelectric phases is still active in composite ceramics when the grain size is ~50 nm.

Description: The room temperature onset plastic deformation and crack behavior of 3C-SiC under contact load were investigated using nanoindentation and transmission electron microscopy (TEM). During loading, abrupt bursts or pop-in in the load–displacement curves was observed at a depth of ~60 nm. The 3C-SiC deforms elastically before the pop-in depth, but exhibits a plastic-elastic behavior after that. TEM observations reveal that the shear slip is the predominant deformation mechanism in 3C-SiC during indentation. The cracks usually initiate at the intersection of shear bands or grain boundary. In addition, theoretical analysis confirms that the pop-in event is associated with the onset plasticity of 3C-SiC.

Description: The crack growth resistance behavior of single crystal and polycrystalline 0.71Pb(Mg 1/3 Nb 2/3 )O 3 -0.29PbTiO 3 (PMN-29%PT) was determined with compact-tension specimens. Two different single crystal orientations were produced by the solid-state crystal growth technique (SSCG) and characterized, allowing for the direct comparison to polycrystalline material. Single crystal R -curve behavior was observed to be anisotropic, which is explained by the effects of ferroelasticity and stress-induced phase transformations on toughening. Results of the polycrystalline samples display comparable toughness to that observed in single crystal measurements.

Description: The certification of a boron carbide reference material for chemical composition is described. The mass fractions of 16 elements and two boron species are certified in an international interlaboratory comparison with 35 participating laboratories from six different countries. Beside chemical characterization the certification process includes homogeneity and stability testing of the candidate material boron carbide (type F360, 305M422). Details of the analytical methods used for chemical characterization and of the calculation of the uncertainties of the certified mass fractions are given. The new reference material ERM ® -ED102 with certified mass fractions of 18 parameters (elements and species) and of the amount fraction of the isotope 10 B is a valuable tool for laboratories working in the field of advanced ceramic materials analysis to improve their analytical results.

Description: The thermoelectric properties of the fluorite-related oxide, In 4 Sn 3 O 12 , have been investigated by studying the system In 4− x Ga x Sn 3 O 12 , with 0 ≤  x  ≤   0.15. It has been shown that Ga does not enter the In 4 Sn 3 O 12 matrix, and two secondary phases form via the Ga introduction: SnO 2 and Ga 2 In 6 Sn 2 O 16 . By reactive sintering between In 2 O 3 , SnO 2 , and Ga 2 O 3 precursors, the density of the samples is considerably increased from 66% (actual density/theoretical density) for x  =   0 up to 90% for x  =   0.15, which significantly decreases the electrical resistivity. This is attributed to the large number of grain boundaries localized among the secondary phases, which inhibit the grain growth and hence favor the densification. The phase In 4 Sn 3 O 12 is for the first time reported to exhibit a semi-metallic behavior. The Seebeck coefficient does not change significantly with respect to the pristine matrix in accordance with the fact that Ga does not play any role as a doping agent. The thermal conductivity increases with the Ga content. The maximum figure of merit, ZT  = 0.23, at 1000 K obtained at a very low Ga content ( x  =   0.05), is comparable to the value obtained for Ge doped In 2 O 3 ( ZT  ~ 0.3). This study suggests that In 4 Sn 3 O 12 can be a potential material for thermoelectric applications.

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: Lead-free (1− x )(K 0.48 Na 0.52 )NbO 3 –( x /5.15)K 2.9 Li 1.95 Nb 5.15 O 15.3 (KNN–KLN100 x , x =0–0.25) piezoelectric ceramics have been prepared by a conventional solid-state sintering technique. The effects of potassium lithium niobate (KLN) content on the phase structure and piezoelectric properties were investigated. The addition of KLN markedly increased the paraelectric cubic-ferroelectric tetragonal phase transition temperature ( T C ), but greatly shifted the polymorphic phase transition from the ferroelectric orthorhombic to the ferroelectric tetragonal phase ( T O–T ) to near room temperature. At room temperature, coexistence of the orthorhombic and tetragonal phases was identified at approximately 0.12≤ x ≤0.18 by the analysis of X-ray diffraction patterns and dielectric spectroscopy, which led to a significant enhancement of the piezoelectric properties. The ceramics with x =0.16 exhibited excellent piezoelectric properties: piezoelectric constant d 33 =235 pC/N, planar electromechanical coupling factor k p =41.6%, and Curie temperature T C =473°C. Moreover, they also have an excellent thermal stability in the severe aging test up close to their Curie temperatures. These results indicated that the KNN–KLN100 x ceramics are very promising lead-free piezoelectric candidates, especially for high-temperature applications.

Description: The properties of yttria-stabilized tetragonal zirconia polycrystalline (YTZP) ceramics, such as low thermal conductivity, excellent biocompatibility, high fracture toughness, high strength, and low wear rates, make them suitable for many applications. To further increase these properties, the use of nanostructured materials and/or the addition of reinforcing second phases such as carbon nanotubes are being investigated. In the present work, it has been demonstrated that with the addition of zirconia partially coated multiwall carbon nanotubes to a nanostructured YTZP matrix the densification is enhanced at lower temperatures and a finer microstructure is obtained.

Description: Zirconium diboride (ZrB 2 ) ceramic matrix composites reinforced by silicon carbide platelets (SiC pl ) were prepared by hot pressing. Five groups of specimens were prepared, in which the contents of SiC platelets were 0, 5, 10, 15 and 20 vol%, respectively. The oxidation behaviors of specimens at different temperatures from 800° to 1600°C for 1 h and at 1200°C for different times from 0.5 to 4 h were investigated. With the increase of SiC pl content, the mass gain exhibited a decreasing trend. Oxidation thermodynamics and kinetics of the SiC pl /ZrB 2 composites were discussed. A characteristic structure of hollow quadrangular prismy ZrO 2 crystal emerged on the sample surface after oxidation was found and the possible formation mechanism was also presented. The surface element analysis indicated that the main products of oxidation were m -ZrO 2 , SiO 2 , and borosilicate (aluminosilicate).

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: The effect of composite binder on the mechanical property of lightweight bubble alumina ceramics was studied. The ceramics were prepared using bubble alumina and α-Al 2 O 3 fines as raw materials, phosphoric acid (H 3 PO 4 ) and aluminum ammonium sulfate (NH 4 Al(SO 4 ) 2 ·12H 2 O) as binders. During sintering, most phosphoric acid react with aluminum ammonium sulfate and the rest react with bubble alumina and α-Al 2 O 3 fines, forming aluminum phosphate on the surface of the alumina particles, which effectively improves the sintering process. The mechanical property of the ceramic bonded by composite binder was greatly improved compared with that bonded by single binder

Description: A Ba 0.6 Sr 0.4 TiO 3 –ZnO–B 2 O 3 composite ink was prepared and used for the manufacturing of fully inkjet-printed metal-insulator-metal varactors. The dielectric thick films were co-fired with printed silver electrodes at 850°C and show a fine grained microstructure. The films have a relative permittivity of ε r  = 129 and a dielectric loss of tan δ = 0.043 at f  =   3 GHz. Printed varactors with different dielectric film thickness were prepared. The characterization of the printed structures and 3D electromagnetic simulations of the layout reveal the strong influence of electrode inductance and fringing effects on the properties of the components. The printed varactors reach tunabilities between 14.4% and 16.4% by applying a tuning field of 5 V/μm. To demonstrate the capability of the inkjet printing process for the preparation of tunable microwave devices, a fully inkjet-printed phase shifter was fabricated. It is based on seven pairs of the printed varactors and reaches a phase shift of 180° and a figure of merit of 19°/dB at 3.4 GHz.

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: This article demonstrates a method to fabricate VO 2 powder by annealing a precursor that was obtained by electrochemical intercalation of lithium into layered structured V 2 O 5 . The method includes three steps. First, Li + was intercalated into interlayers of V 2 O 5 through an electrochemical process with precisely controlled electrical discharging currents and intercalation amounts, and at the same time V 5+ would be deoxidized into V 4+ . Secondly, the Li + -intercalated powder was rinsed in an acid solution to achieve an ion exchanging process of replacing the Li + in the V–O frame with H + . Thirdly, the powder was annealed at 800°C in N 2 atmosphere for dehydration and VO 2 crystallization. By DSC investigation, the as-produced final product has a strong endothermic peak at around 68°C in a heating semicycle, which is indicative of the phase transition from VO 2 (M) to VO 2 (R). This approach can be extended to the fabrication of other sub-valence oxides by lithium intercalation and deoxidization of its higher valence layer-structured precursors.

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.