Thermal Expansion of Homogeneous and Gradient Solid Solutions in the System KZr2(PO4)3─KTi2(PO4)3

Low-thermal-expansion ceramics having arbitrary thermal expansion coefficients were synthesized from homogeneous solid solutions in the system KZr₂(PO₄)₃─KTi₂(PO₄)₃ (KZP–KTP). Dense and strong ceramics were fabricated by sintering at 1100° to 1200°C with 2 wt% MgO. The thermal expansion coefficient increased from 0 to +3 × 10⁻⁶/°C with increasing x in KZr_{2 − x}Ti_x (PO₄)₃ (KZTP). In addition, a functionally gradient material with respect to thermal expansion was prepared by forming a series of KZTP solid solutions in a single ceramic body. By heating a pile of KZP and KTP ceramics in contact with each other, KZP and KTP bonded together to form a KZTP gradient solid solution near the interface.     

Ionic Conductivity and Sinterability of NASICON-Type Ceramics: The Systems NaM2(PO4)3+yNa2o (M = Ge, Ti, Hf, and Zr)

Sodium-rich NASOCON-type ceramics, the NaM₂(PO₄)₃+_yNa₂O (M = Ge, Ti, Hf, Zr) system, were investigated in order to obtain a material having a high Na⁺ conductivity and high density. The ionic conductivity and the sinterability were greately improved by an increase in the valve of y for all of the system examined. Added Na₂O was not souble in teh NASICON-type skeletton, sice the lattice constants and teh X-ray diffraction patterns were not changed by the Na₂O addintion in all of the samples. Na₂O acts as a flux for obtaining highly dense ceramics and highly conductive grain boundaries. Partial A₂ site insertion by Na⁺ ions is effective for the enhancement of conductivity, because the conductivity for Na_1.5M(III)_0.5Zr_1.5(PO₄)₃ (M = In or Y) is about 1 order of magnitude higher than the maximum conductivity of the NaZr₂(PO₄)₃+_yNa₂O system.     

Effects of M3+ Ions on the Conductivity of Glasses and Glass-Ceramics in the System Li2O—M2O3—GeO2—P2O5 (M = Al, Ga, Y, Dy, Gd, and La)

Glasses with compositions Li_1.2M_0.2Ge_1.8(PO₄)₃ (M = Al, Ga, Y, Gd, Dy, and La) were prepared and converted to glass-ceramics by heat treatment. The effects of the M³⁺ ions on the conductivity of the glasses and glass-ceramics were studied. The main phase present in the glass-ceramics was the conductive phase LiGe₂(PO₄)₃. Al³⁺ and Ga³⁺ ions entered the LiGe₂(PO₄)₃ structure by replacing Ge⁴⁺ ions, but lanthanide ions did not. The glass-ceramics exhibited much higher conductivity than the glasses. With increased ionic radius of the M³⁺ ions, the conductivity remained almost unchanged at ∼3 × 10⁻¹² S/cm for the glasses, but it decreased from 1.5 × 10⁻⁵ to 8 × 10⁻⁹ S/cm for the glass-ceramics at room temperature. The higher conductivity for Al³⁺- and Ga³⁺-containing glass-ceramics was suggested to result from the substitutions of Al³⁺ and Ga³⁺ ions for Ge⁴⁺ ions in the LiGe₂(PO₄)₃ structure.     

Porous Glass-Ceramics with a Skeleton of the Fast-Lithium-Conducting Crystal Li1+xTi2−xAlx(PO4)3

Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li₂O─CaO─TiO₂─Al₂O₃–P₂O₅ system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ and β-Ca₃(PO₄)₂ phases. The median pore diameter and surface area of the resulting porous Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ glass-ceramics were approximately 0.2 μm and 50 m²/g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO₃ aqueous solution was 8 × 10⁻⁵ S/cm at 300 K or 2 × 10⁻² S/cm at 600 K.     

Negative Thermal Expansion in (HfMg)(WO4)3

A single-phase material (HfMg)(WO₄)₃ with an orthorhombic structure, A₂ (WO₄)₃-type tungstate, has been successfully prepared for the first time by the calcination of HfO₂, MgO, and WO₃, substituting Hf⁴⁺ and Mg²⁺ for A³⁺ cations in A₂(WO₄)₃. The new material shows a negative thermal expansion coefficient of approximately −2 ppm/°C from room temperature to 800°C. The mechanism of negative thermal expansion is assumed to be the same as that of Sc₂(WO₄)₃.     

Grain Size-Microcracking Relation for NaZr2(PO4)3 Family Ceramics

The grain size-microcracking relation was examined for low thermal expansion NaZr₂(PO₄)₃ family ceramics. By measurements of the strength, Young's modulus, thermal expansion, and grain size of polycrystalline ceramics sintered at appropriate conditions, the critical grain size for microcracking was determined. The critical grain size was proportional to the inverse square of the maximum thermal expansion difference.     

Spark Plasma Sintering of LiTi2(PO4)3-Based Solid Electrolytes

Solid electrolytes, LiTi₂(PO₄)₃ (LTP), Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), and Li_1.3Al_0.3Ti_1.7(PO₄)_2.9(VO₄)_0.1 (LATPV), were prepared by conventional sintering (CS) and spark plasma sintering (SPS) methods, and the Li⁺ ion conductivity of the sintered pellets was examined using an impedance analyzer. SPS remarkably improved the densification compared to CS and resulted in dense ceramics (95–97% of theoretical density) irrespective of the substituted ions. The highest conductivity of 2.6 × 10⁻⁴ S/cm was found for the LATPV specimen sintered by spark plasma at 1100°C. LATP and LATPV exhibited an order of magnitude higher ionic conductivity than LTP in the specimens of similar densities. The results demonstrated that the enhanced conductivity in substituted LTP is not due to the enhanced densification alone. The other possible explanations are discussed in terms of bottleneck size, lithium content, and grain boundary characteristics.     

Flexible Ceramics in the System KZr2(PO4)3–KAlSi2O6 Prepared by Mimicking the Microstructure of Itacolumite

A ceramic composite mimicking the pervasively cracked microstructure of flexible sandstone (itacolumite) was successfully synthesized by sintering two ceramic materials with different thermal expansion coefficients. A combination of granular KZr₂(PO₄)₃ (high thermal expansion) and powdered KAlSi₂O₆ (low thermal expansion) resulted in a material with a jigsaw-like three-dimensional cracking microstructure similar to that of itacolumite. The synthesized composite was found to exhibit ductile deformation.     

Formation of Sm2+ lons in Sol-Gel-Derived Glasses of the System Na2 O-Al2O3-SiO2

Samarium ions (Sm²⁺) incorporated into aluminosilicate glasses by a sol-gel process showed persistent spectral hole burning at room temperature. Gels of the system Na₂O-Al₂O₃SiO₂ synthesized by the hydrolysis of Si(OC₂H₅)₄, Al(OC₄H₉)₃, CH₃ COONa, and SmCl₃·6H₂O were heated in air at 500°C, then reacted with H₂ gas to form Sm²⁺ ions. Whereas Al³⁺ ions effectively dispersed the Sm³⁺ ions in the glass structure, Na⁺ ions were not effective. The Al₂O₃-SiO₂ glasses proved appropriate for reacting the Sm³⁺ ions with H₂ gas and exhibited the intense photoluminescence of Sm²⁺ ions. The reaction of Sm³⁺ ions with H₂ in the Al₂O₂-SiO₂ glasses was determined by first-order kinetics, and the activation energy equaled 95 kJ/mol. At 800°C, the maximum photoluminescence of the Sm²⁺ ions was achieved within 20 min.     

Preparation of Porous Glass-Ceramics with a Skeleton of NASICON-Type Crystal CuTi2(PO4)3

A novel porous glass-ceramic with a skeleton of CuTi₂(PO₄)₃ was prepared by controlled crystallization of a glass and subsequent chemical leaching of the resulting dense glass-ceramic. A volume-crystallized dense glass-ceramic composed of CuTi₂(PO₄)₃ and Cu₃(PO₄)₂ whose surface was covered by a CuO thin layer was prepared by reheating a glass with a nominal composition of 50CuO·20TiO₂30P₂O₅ (in mol%) glass in air. When the resultant glass-ceramic was leached with dilute H₂SO₄, Cu₃(PO₄)₂ and CuO phases were dissolved out selectively, leaving a crystalline CuTi₂(PO₄)₃ skeleton. The specific surface area and the average pore radius of the porous glass-ceramic obtained were approximately 45 m₂g_-1 and 9 nm, respectively. The porous glass-ceramic showed catalytic activity in the conversion reaction of propene into acrolein.     

Hydration in the System Ca2SiO4–Ca3(PO4)2 at 90°C

Compositions along the Ca₂SiO₄–Ca₃(PO₄)₂ join were hydrated at 90°C. Mixtures containing 15, 38, 50, 80, and 100 mol% Ca₃(PO₄)₂ were fired at 1500°C, forming nagelschmidtite + a ¹-CaSiO₄, A -phase and silicocarnotite and a -Ca₃(PO₄)₂, respectively. Hydration of these produces hydroxylapatite regardless of composition. Calcium silicate hydrate gel is produced when Ca₂SiO₄≠ 0 and portlandite when Ca₂SiO₄ is >50%. Relative hydration reactivities are a -Ca₃(PO₄)₂ > nagelschmidtite > α ¹-Ca₂SiO₄ > A -phase > silicocarnotite. Hydration in the presence of silica or lime influences the amount of portlandite produced. Hydration in NaOH solution produces 14-A tobermorite rather than calcium silicate hydrate gel.     

Porous Glass-Ceramic in the CαO–TiO2–P2O5 System

A porous glass-ceramic in the CaO–TiO₂—P₂O₅ system has been prepared by crystallization and subsequent chemical leaching of the corresponding glass. By applying a two-step heat treatment to 45CaO · 25TiO₂· 30P₂O₅ glasses containing a few mol% of Na₂O, volume crystallization results in the formation of dense glass-ceramics composed of CaTi₄(PO₄)₆ and β-Ca₃(PO₄)₂ phases. By leaching the resultant glass ceramics with HCI, β-Ca₃(PO₄)₂ is selectively dissolved out, leaving a crystalline CaTi₄(PO₄)₆ skeleton. The surface area and mean pore radius of the porous glass-ceramics were approximately 40 m²/g and 13 nm, respectively.     

Thermal Expansion of the Low-Temperature Form of BaB2O4

Thermal expansion of the low-temperature form of BaB₂O₄ (β-BaB₂O₄) crystal has been measured along the principal crystallographic directions over a temperature range of 9° to 874°C by means of high-temperature X-ray powder diffraction. This crystal belongs to the trigonal system and exhibits strongly anisotropic thermal expansions. The expansion along the c axis is from 12.720 to 13.214 Å (1.2720 to 1.3214 nm), whereas it is from 12.531 to 12.578 Å (1.2531 to 1.2578 nm) along the a axis. The expansions are nonlinear. The coefficients A, B , and C in the expansion formula L _t = L ₀(1 + At + Bt ²+ Ct ³) are given as follows: a axis, A = 1.535 × 10⁻⁷, B = 6.047 × 10⁻⁹, C = -1.261 × 10⁻¹²; c axis, A = 3.256 × 10⁻⁵, B = 1.341 × 10⁻⁸, C = -1.954 × 10⁻¹²; and cell volume V, A = 3.107 × 10⁻⁵, B = 3.406 × 10⁻⁸, C = -1.197 × 10⁻¹¹. Based on α _t = (d L _t /d t )/ L ₀, the thermal expansion coefficients are also given as a function of temperature for the crystallographic axes a , c , and cell volume V.     

Peculiar Dielectric Behaviors of (Na1/2Bi1/2)0.87Pb0.13TiO3 Thin Films

PbTiO₃-doped sodium bismuth titanate (Na_1/2Bi_1/2)_{1− x} Pb _x TiO₃ of perovskite structure is one of the best-known piezoelectrics/ferroelectrics. However, it has not been properly investigated in any thin-film forms. In this study, the dielectric properties of (Na_1/2Bi_1/2)_0.87Pb_0.13TiO₃ thin films synthesized via a sol–gel route were investigated. They exhibit a strong frequency dispersion of the dielectric permittivity at relatively high frequencies, which is shifted to lower frequencies with increasing temperature. The electrical behavior can be fitted using Jonscher's universal law for dielectric relaxation. The peculiar dielectric behaviors observed can be ascribed to the coexistence of two different dielectric phases in the films, which is believed to be associated with the growth of the local Pb²⁺TiO₃ nanoclusters upon substitution of Pb²⁺ for Na⁺/Bi³⁺ in the (Na_1/2Bi_1/2)_{1− x} Pb _x TiO₃ films.     

Proton Conductivity in Zr4+-Ion-Doped P2O5–SiO2 Porous Glasses

The effect of zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P₂O₅–SiO₂ glasses. Porous glasses were prepared through hydrolysis of PO(OCH₃)₃, Zr(OC₄H₉)₄, and Si(OC₂H₅)₄. Chemical bonding of the P⁵⁺ ions was characterized using ³¹P-NMR spectra. The phosphorous ions, occurring as PO(OH)₃ in the ZrO₂-free glass, were polymerized with one or two bridging oxygen ions per PO₄ unit with increased ZrO₂ content. The chemical stability of these glasses was increased significantly on the addition of ZrO₂, but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P₂O₅·7ZrO₂·83SiO₂ glass. A fuel cell was constructed using 10P₂O₅·5ZrO₂·85SiO₂ glass as the electrolyte; a power of ∼4.5 mW/cm² was attained.     

REVISION OF CRYSTALLINE PHASES IN THE SYSTEM ZRO2-P2O5

Crystalline phases in the system ZrO₂-P₂O_s were reexamined. Samples of varied composition were prepared by the sol-gel route and calcining, as well as by reacting mixtures ofZrO₂ and NH4H2PO4, at temperatures from 200° to 1400°C. Confusion regarding compositions and structures was clarified, and the phase Zr₃(PO₄)₄ was confirmed. The latter can be written Zro.₂sZr₂(PO₄)₃ and is iso-structural withNaZr₂P₃O₁₂. The role of mineralizers and the influence of zirconium salts can now be understood.     

Preparation of Porous Ca10(PO4)6(OH)2 and β-Ca3(PO4)2 Bioceramics

Submicrometer-sized, pure calcium hydroxyapatite (HA, (Ca₁₀(PO₄)₆(OH)₂)) and β-tricalcium phosphate (β-TCP, Ca₃(PO₄)₂) bioceramic powders, that have been synthesized via chemical precipitation techniques, were used in the preparation of aqueous slurries that contained methyl cellulose to manufacture porous (70%–95% porosity) HA or β-TCP ceramics. The pore sizes in HA bioceramics of this study were 200–400 μm, whereas those of β-TCP bioceramics were 100–300 μm. The pore morphology and total porosity of the HA and β-TCP samples were investigated via scanning electron microscopy, water absorption, and computerized tomography.     

High-Temperature Mechanical Properties of Ceramic Materials: V, (Zn0.65, Mg0.35)2SiO4

The composition (0.65Zn,0.35Mg)₂ SiO₁ was investigated. Its thermal expansion was 32 × 10^-7/°C from room temperature to 1000°C. Modulus of rupture was approximately 7000 psi between room temperature and 800°C, whereas Young's modulus held at approximately 11 × 10° psi over the same range. The substitution of 0.35 m oles Mg⁺⁺ for Zn⁺⁺ in Zn₂Si0₄ causes little change in many of the physical properties, but the solid solution sinters much more readily than pure Zn₂Sio₄. The willemite solid solution studied has very good thermal shock resistance between room temperature and 1000°C.     

Photoluminescence Characteristics of Energy Transfer Between Eu3+and Bi3+in LiEu1−xBix (WO4)0.5(MoO4)1.5

A series of novel red phosphors LiEu_{1− x} Bi _x (WO₄)_0.5(MoO₄)_1.5 ( x =0, 0.05, 0.10, 0.15, 0.20, 0.30, 0.40, and 0.50) were synthesized by the conventional solid-state reaction method. The spectrum and the crystal structure of the phosphors were characterized by Fluorescence spectrophotometry and X-ray diffraction, respectively. The photoluminescent results show that all samples can be excited efficiently by UV (396 nm) and blue (467 nm) light and that they emit red light at 615 nm with line spectra, which are coupled well with the characteristic emissions from UVLED and blue light-emitting diode (LED), respectively. There is an efficient energy transfer from Bi³⁺ to Eu³⁺ ions, leading to the emission intensity of Eu³⁺ being enhanced by 1.5 times, and even more when Bi³⁺ ions are introduced into LiEu (WO₄)_0.5(MoO₄)_1.5. The introduction of Bi³⁺ ions broadened the excitation band of the phosphor, and the optimum doping concentration is found to be 10 mol% of Bi³⁺.     

Anisotropic Thermal Expansion of β-Ca2SiO4 Monoclinic Crystal

Crystals of β-Ca₂SiO₄ (space group P 12₁/ n 1) were examined by high-temperature powder X-ray diffractometry to determine the change in unit-cell dimensions with temperature up to 645°C. The temperature dependence of the principal expansion coefficients (α_i) found from the matrix algebra analysis was as follows: α₁= 20.492 × 10⁻⁶+ 16.490 × 10⁻⁹ ( T - 25)°C⁻¹, α₂= 7.494 × 10⁻⁶+ 5.168 × 10⁻⁹( T - 25)°C⁻¹, α₃=−0.842 × 10⁻⁶− 1.497 × 10⁻⁹( T - 25)°C⁻¹. The expansion coefficient α₁, nearly along [302] was approximately 3 times α₂ along the b -axis. Very small contraction (α₃) occurred nearly along [     01]. The volume changes upon martensitic transformations of β↔α_L' were very small, and the strain accommodation would be almost complete. This is consistent with the thermoelasticity.