Metastable Modification of Y2CeO5

A metastable modification of Y₂GeO₅ is formed from an amorphous material prepared by the simultaneous hydrolysis of yttrium and germanium alkoxides. It has an orthorhombic unit cell with a =0.6068 nm, b =1.0695 nm, and c = 1.1994 nm. The chemical structure is described by the formula Y₄(Ge₂O₆)O₄.     

Phase Relationships in the Si3N4–SiO2–Lu2O3 System

Phase relationships in the Si₃N₄–SiO₂–Lu₂O₃ system were investigated at 1850°C in 1 MPa N₂. Only J-phase, Lu₄Si₂O₇N₂ (monoclinic, space group P 2₁/ c , a = 0.74235(8) nm, b = 1.02649(10) nm, c = 1.06595(12) nm, and β= 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si₃N₄–SiO₂–Lu₂O₃ system. The Si₃N₄/Lu₂O₃ ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu–J-phase, β-Si₃N₄, and a new phase of Lu₃Si₅ON₉, having orthorhombic symmetry, space group Pbcm (No. 57), with a = 0.49361(5) nm, b = 1.60622(16) nm, and c = 1.05143(11) nm. The new phase is best represented in the new Si₃N₄–LuN–Lu₂O₃ system. The phase diagram suggests that Lu₄Si₂O₇N₂ is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications.     

Crystal Structure of Zr2Al3C4

The crystal structure of Zr₂Al₃C₄ was refined by the Rietveld method from conventional X-ray powder diffraction data. The structure was hexagonal (space group P 6₃ mc , Z =2) with a =0.334680(6) nm, c =2.22394(3) nm, and V =0.215731(6) nm³, being isomorphous with that of U₂Al₃C₄. The final reliability indices were R _wp=8.57%, R _p=6.06%, and S =1.32. The crystal showed an intergrowth structure with NaCl-type ZrC slabs separated by Al₄C₃-type Al₃C₂ layers.     

New Compound in the System La2O3-Al2O3

A new compound, 5La₂O₃-2Al₂O₃, is formed from an amorphous material prepared by the simultaneous hydrolysis of lanthanum and aluminurn alkoxides. It has an orthorhombic unit cell with a=0.9704 nm, b=0.5967 nm, and c=1.5473 nm. The structure contains tetrahedral AlO₄ groups and octahedral AlO₆ groups.     

Syntheses and Unit-Cell Determination of Ba3V4O13 and Low-and High-Temperature Ba3P4O13

The syntheses and the results of unit-cell determinations ofBa₃V₄O₁₃ and the two forms (low- and high-temperature) of Ba₃P₄O₁₃ are presented. Ba₃V₄O₁₃ crystallizes in the monoclinic system, space group Cc or C2/c with unit-cell dimensions a=16.087, b=8.948, c=10.159 (x10nm), β=114.52° Low-Ba₃P₄O₁₃ crystallizes in the triclinic system, space group P1 or P1 with unit-cell dimensions a=5.757, b=7.243, c=8.104 (x10 nm) α=82.75°, β=73.94°, γ=70.71°. Low-Ba₃P₄O₁₃ transforms at 870°C into high-Ba₃P₄O₁₃ which crystallizes in the orthorhombic system, space group Pbcm (No. 57) (or Pbc2, No. 29) with unit-cell dimensions a =7.107, b=13.883, c=19.219 (x10 nm). No relations have been found between the structures of the tribarium tetravanadate and the tribarium tetraphosphate.     

Investigation of the Phase Diagram for the Pseudobinary System Li2SO4–La2(SO4)3 and Its Ionic Conductivity

The phase diagram of the pseudobinary system Li₂SO₄–La₂(SO₄)₃ has been investigated by means of X-ray diffraction and differential thermal analysis. LiLa(SO₄)₂ is formed by a peritectic reaction in this system; the peritectic temperature is 653±3°C. The eutectic reaction of Li₂SO₄ and LiLa(SO₄)₂ occurs at 553±3°C; the composition at the eutectic point is 17 mol% La₂(SO₄)₃. LiLa(SO₄)₂ is monoclinic with a=1.375 nm, b=0.6744 nm, c=0.7068 nm, and β=105.4°. The ionic conductivity of LiLa(SO₄)₂ has been studied from room temperature to 350°C and is found to be relatively low at room temperature or at lower temperatures. Its activation energy is 0.66 eV. Thus it is not suitable as a fast ion conductor.     

Three Crystalline Polymorphs of KFeSiO4, Potassium Ferrisilicate

Orthorhombic α-KFeSiO₄ ( a =0.5478, b =0.9192, c =0.8580 nm), hexagonal β-KFeSiO₄ ( a =0.5309, c =0.8873 nm), and hexagonal γ-KFeSiO₄ ( a =0.5319, c =0.8815 nm) were synthesized by devitrification of KFeSiO₄ glass. Powder X-ray diffraction data are given for all three polymorphs. Alpha KFeSiO₄, the high-temperature polymorph, melts congruently at 1197°± 2°C. Mössbauer spectroscopy of the α phase indicates that Fe³⁺ occupies two tetrahedral sites in the lattice. Beta KFeSiO₄, the low-temperature polymorph, and γ-KFeSiO₄, a metastable polymorph, appear to be isomorphous with kalsilite, KAISiO₄, and synthetic kaliophilite, KAISiO₄, respectively, and it is proposed that β- and γ -KFeSiO₄ are linked by Si-Fe order-disorder. Beta KFeSiO₄ transforms slowly into α -KFeSi0₄ above 910°C but the transformation was not shown to be reversible in the present dry-heating experiments.     

Synthesis and Crystal Structure of a New Layered Carbide ZrAl4C4

A new ternary layered carbide, ZrAl₄C₄, has been synthesized and characterized by X-ray powder diffraction. The crystal structure was successfully determined using direct methods and further refined by the Rietveld method. The crystal is trigonal (space group P 3 m 1, Z =2) with lattice dimensions a =0.332471(3) nm, c =2.19717(2) nm, and V =0.210330(3) nm³. The final reliability indices calculated from the Rietveld refinement were R _wp=6.56% ( S =1.58), R _p=4.92%, R _B=1.90%, and R _F=0.98%. The compound shows an intergrowth structure with NaCl-type [Zr₂C₃] thin slabs separated by Al₄C₃-type [Al₈C₇] layers.     

Structural Disorder and Intracrystalline Microtexture of α'H-(Ba0.24Ca0.76)2SiO4

The structural disorder and twin microtexture of (Ba_0.24Ca_0.76)₂SiO₄ crystal were investigated by X-ray powder diffraction, precession method, and optical microscopy. The crystal at 298 K was orthorhombic (space group Pnma , Z =4) with a =0.70490(5) nm, b =0.55399(4) nm, c =0.95532(7) nm, and V =0.37306(4) nm³. The crystal structure was satisfactorily described by a split-atom model, involving the positional disorder of Ba/Ca and O atoms across the (010) mirror plane. The crystal was found to be isostructural with α'_H-Ca₂SiO₄, thus regarded as the stabilized α'_H phase. The crystal grain was composed of orthorhombic domains in three different orientations. The unit cells within each domain were related to one another by the threefold pseudo-symmetry axis lost during the α-to-α'_H transition. Each domain was most probably made up of sub-domains of the two mirror-related structural configurations with P 2₁/ n symmetry.     

Synthesis and Crystal Structure of a New Layered Carbide [Zr1.97Y0.03]Al4C5

A new layered carbide, [Zr_1.97Y_0.03]Al₄C₅, has been synthesized and characterized by X-ray powder diffraction (XRPD), transmission electron microscopy, and energy-dispersive X-ray spectroscopy (EDX). The atom ratios [Zr:Y] were determined by EDX, and the crystal structure was refined from laboratory XRPD data (Cu K α₁) using the Rietveld method. The crystal is trigonal (space group R 3 m , Z =3) with lattice dimensions of a =0.331934(4) nm, c =4.09459(3) nm, and V =0.390701(7) nm³. The final reliability indices were R _wp=10.29% ( S =1.31), R _p=7.45%, R _B=1.63%, and R _F=1.04%. The compound shows an intergrowth structure with NaCl-type [Zr_1.97Y_0.03C₃] thin slabs separated by Al₄C₃-type [AlC] layers. This material is isostructural with Zr₂[Al_3.56Si_0.44]C₅.     

New Modification of Pb5GeO7

A new modification of'Pb₅Ge0₇ was formed by the simultaneous hydrolysis of lead and germanium alkoxides, followed by washing and drying. It has a hexagonal unit cell with a =0.7589 nm and c = 1.2421 nm. The chemical structure is described by the formula Pb₅(GeO₄)O₃. Hexagonal Pb₅GeO₇ transforms to the orthorhombic modification at 460° to 485°C.     

Formation of AlVO4 Solid Solution from Alkoxides

Solid solutions of AlVO₄ crystallize at lower temperatures than amorphous materials between 50 and 70 mol% Al₂O₃ prepared by the simultaneous hydrolysis of aluminum and vanadyl alkoxides. They decompose into α-Al₂O₃, and V₂O₅, at 775° to 800°C. The compound AlVO₄ prepared from 50 mol% Al₂O₃ has a triclinic unit cell with a = 0.6471 nm, b = 0.7742 nm, c = 0.9084 nm, α= 96.848°, β= 105.825°, and γ= 101.399°. The volume of the unit cell increases continuously with increases in Al₂O₃ content. The structure contains tetrahedral AlO₄, octahedral AlO₆, and tetrahedral VO₄ groups.     

Crystal Structure and Thermoelectric Properties of YAl3C3

The crystal structure of YAl₃C₃ was refined from laboratory X-ray powder diffraction data (Cu K α₁) using the Rietveld method. The crystal structure is hexagonal (space group P 6₃ mc , Z =2) with lattice dimensions a =0.342157(4) nm, c =1.72820(1) nm, and V =0.175217(3) nm³. The final reliability indices were R _wp=9.94% ( R _wp/ R _e=1.18), R _p=7.36%, R _B=1.77%, and R _F=1.03%. The compound shows an intergrowth structure with electroconductive [YC₂] thin slabs separated by Al₄C₃-type [AlC] layers. This material had thermoelectric properties superior to those of the layered carbides Zr₂[Al_3.56Si_0.44]C₅, Zr₂Al₃C₄, and Zr₃Al₃C₅ in the temperature range of 500– 1073 K, with a maximal power-factor value of 1.96 × 10⁻⁴ W·(m·K²)⁻¹ at 1073 K.     

Liquid Formation at the Peritectic Temperature in Superconducting YBa2Cu3O7−x—Observation of a New Phase YBa4CuAIO8

In the system Y-Ba-Cu-O, partial melting of peritectically decomposing YBa₂Cu₃O_{7- x} (123) was used to produce a bulk material of high critical current density when the material was aligned. The liquid formation mechanism and its relation to reaction with alumina refractory was studied. A previously unreported phase of the approximate stoichiometric ratio Y:Ba:Cu:Al = 1:4:1:1 (YBa₄CuAlO₈) was detected. The crystal structure was determined to be tetragonal, with lattice parameters a ₀= b ₀= 1.651 nm, c ₀= 1.793 nm. The 1411 phase bears a close structural relationship to BaCuO₂.     

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⁺.     

Low-Temperature Synthesis of Bismuth Titanate Niobate (Bi7Ti4NbO21) Nanoparticles from a Metal-organic Polymeric Precursor

This paper describes the preparation of homogeneous Bi₇Ti₄NbO₂₁ single-phase ceramic powders of ∼55 nm crystallite size, at temperatures as low as 400°–500°C using a metal citrate complex method based on the Pechini-type reaction route. The thermal decomposition/oxidation of the polymerized resin, as investigated by TG/DTA, XRD, and SEM, led to the formation of a well-defined orthorhombic Bi₇Ti₄NbO₂₁ compound with lattice parameters a = 0.544, b = 0.540, and c = 2.905 ± 0.0005 nm. Reaction takes place through an intermediate binary phase with a stoichiometry close to Bi₂₀TiO₃₂ which forms between 300° and 375°C. The metal-organic precursor synthesis method, where Bi, Ti, and Nb ions are first chelated to form metal complexes and then polymerized to give a gel, allows control of the Bi/Ti/Nb stoichiometric ratio leading to the rapid formation of nanosized bismuth titanate niobate (Bi₇Ti₄NbO₂₁) ceramic powders, at temperatures much lower than usually needed by conventional processing of mixed-oxide powders.     

Microstructure of a Complex Oxide, Er2Mn2/3Mo4/3O7, with a Pyrochlore-Related Structure

The ternary compound Er₂Mn_2/3Mo_4/3O₇, with a pyrochlore-related structure, was synthesized in a vacuum-sealed quartz tube at 1373 K. The compound was characterized by X-ray diffractometry, electron probe microanalysis, and transmission electron microscopy. The compound possessed a monoclinic structure, with lattice parameters of a = 1.2781(2) nm, b = 0.7378(5) nm, c = 1.1643(6) nm, and β= 100.53(1)°. The compound had a large number of lamellar domains, which were composed of a microtwinned structure on the twin axis 〈1¯1¯0〉.     

A β-Phase Based Superstructure in Bi2O3 Doped with PbF2

A new phase was prepared from Bi₂O₃·15 mol% PbF₂ by heating it at 700°C and then quenching to room temperature. The crystal structure (tetragonal, a =0.765 and c = 1.77 nm, P4₂/nmc) is related to that of the β-phase of Bi₂O₃ by a supercell which is 3 times larger in the c direction.     

Structural Analysis of a New Layered Compound: La0.05Sr0.95MnO3

We have found a new phase of La_0.05Sr_0.95MnO₃ with a 30-layer rhombohedral structure by using electron microscopy. The lattice constants were hexagonal axes of a = 0.5444 nm and c = 6.7582 nm. Both weak and strong intensities appeared in selected area diffraction (SAD) patterns. The strong intensities were caused by the periodicity of 15 (Sr,La)O₃ layers that had a new stacking sequence of (cchch)₃. However, the weak intensities indicated that the 15-layer structure has modulation along the c -direction that is twice as long as that of the structure indicated by the strong intensities. We concluded that the modulation of the 30-layer structure was produced by the introduction of two kinds of oxygen octahedra, Mn³⁺O₆ and Mn⁴⁺O₆.     

SiO2–PbO–CaO–ZrO2–TiO2–(B2O3–K2O), A New Zirconolite Glass–Ceramic System: Crystallization Behavior and Microstructure Evaluation

Zirconolite (CaZrTi₂O₇) is a mineral that has a high containment capacity for actinides and lanthanides and is considered to be a good candidate for the immobilization of radioactive wastes. The glass–ceramic technique seems to be a very suitable and convenient method to produce zirconolite crystals by precipitating them in a specific glass matrix. In this study, development of a new zirconolite-based glass–ceramic belonging to SiO₂–PbO–CaO–ZrO₂–TiO₂–(B₂O₃–K₂O) system was investigated. The presence of PbO, together with B₂O₃ and K₂O, allowed the preparation of a X-ray diffraction (XRD) amorphous glass with a relatively high concentration of ZrO₂ and TiO₂, which was successfully converted to a glass–ceramic containing 34 wt% of zirconolite after heating at 770°C for 4 h. Differential thermal analysis, XRD, scanning electron microscope, and energy dispersive X-ray spectroscopy were used to determine the crystallization conditions, identify the crystallized phases, determine their compositions and quantities and observe and analyze the microstructures. The zirconolite crystals showed a platelet morphology with a monoclinic structure characterized by a =1.246 nm, b =0.7193 nm, c =1.128 nm, and β=100.508°.