Fractal Surfaces of ZrO2 , WO3 , and CeO2 Powders

The surface fractal properties of ZrO₂, WO₃, and CeO₂ powders prepared by the thermal decomposition of ZrO(NO₃)₂, (NH₄)₄W₅O₁₇, and (NH₄)₂Ce(NO₃)₆, respectively, were studied by mercury porosimetry. The results demonstrate that these oxides may, in principle, have fractal surfaces owing to topochemical processes of the type A(s) B(s) + C(g). The surface fractal dimension of individual crystallites and their aggregates are determined.     

Cathodoluminescence of Cd4SiS6 , Cd4SiSe6 , and Si-Doped CdS, CdSe, and CdTe Crystals

CdS, CdSe, and CdTe single crystals were vapor-phase-doped with the corresponding silicon chalcogenides under nearly equilibrium conditions. Cathodoluminescence studies revealed that the Si dopant produced new luminescence centers in the crystals. The cathodoluminescence spectra of Cd₄SiS₆and Cd₄SiSe₆crystals were measured. Metastable, sphalerite CdSSi and CdSeSi films were grown under highly nonequilibrium conditions. The maximum of edge emission in their spectra was redshifted as compared to the stable materials. The CdSSi and CdSeSi crystals were shown to be photosensitive.     

Interaction of Water with GeCl4 , SnCl4 , and AsCl3

The interaction of water with GeCl₄, SnCl₄, and AsCl₃ was studied by IR spectroscopy. The results demonstrate that these chlorides contain molecular water in monomeric form. At water concentrations above 10^–2 mol/l, GeCl₄ also contains H₃O⁺ ions. The mechanisms of GeCl₄ and AsCl₃ hydrolysis were studied over a wide range of water concentrations.     

Lead Recovery from PbO, PbCl2 , PbS, PbSO4 , and Their Mixtures in Carbonate Melts

The reduction (with and without carbon) of PbO, PbCl₂, PbS, PbSO₄, and their mixtures in Na₂CO₃ and K₂CO₃ melts was studied by thermodynamic modeling and experimentally.     

CrS–Yb3S4Phase Diagram and Magnetic Properties of Yb3Cr2S6 , Yb3CrS5 , and Yb9CrS13

Phase relations in the CrS–Yb₃S₄system were studied by differential thermal analysis, x-ray diffraction, and microstructural analysis. The compounds Yb₃Cr₂S₆, Yb₃CrS₅, and Yb₉CrS₁₃were obtained, and their magnetic properties were investigated. The three sulfides were found to be paramagnetic in the temperature range 80–300 K.     

Preparation of LiTaO3 , LiNbO3 , and NaNbO3 from Peroxide Solutions

A procedure is described for preparing peroxide solutions of LiTaO₃ and LiNbO₃. It is shown that the use of peroxide solutions makes it possible to obtain stoichiometric LiTaO₃, LiNbO₃, and NaNbO₃ and Li _x Na_{1 – x} Nb₃ solid solutions.     

Transmission and Absorption Spectra of Bi12GeO20 , Bi12SiO20 , and Bi12TiO20 Single Crystals

The absorption and transmission spectra of Bi₁₂MO₂₀ (M = Ge, Si, Ti) sillenite crystals were studied in the range 300–900 nm. Doping and vacuum annealing were found to have a significant effect on the transmission spectra of the crystals both near the fundamental absorption edge and in the long-wavelength region. The spectral dependences of the photocurrent through Bi₁₂GeO₂₀, Bi₁₂SiO₂₀, and Bi₁₂TiO₂₀ are also discussed.     

Phase Relations in the Systems Al2TiO5–Fe2O3 , Al2O3–TiO2–Fe2O3 , and Al2TiO5–Cr2O3

Phase relations in the systems Al₂TiO₅–Fe₂O₃, Al₂TiO₅–Cr₂O₃, and Al₂O₃–TiO₂–Fe₂O₃ are investigated, and the composition ranges of pseudobrookite Al_{2 – 2x} M_2x TiO₅ (M = Fe, Cr) solid solutions are determined.     

Phase Relations in the NaF–WO3 , NaCl–Na3WO3F3 , and NaCl–NaWO3F Systems

The NaF–WO₃, NaCl–Na₃WO₃F₃, and NaCl–NaWO₃F systems were studied by thermal analysis and x-ray diffraction. Solid-state transformations were revealed, and the primary crystallization ranges were outlined. The refractive indices of the sodium fluorotungstates were measured. The thermodynamic functions of Na₃WO₃F₃were derived from emf measurements.     

Phase Transitions of Cs3Sb2I9 , Cs3Bi2I9 , and Cs3Bi2Br9 Crystals

The phase transitions of Cs₃Sb₂I₉, Cs₃Bi₂I₉, and Cs₃Bi₂Br₉crystals were investigated by ¹³³Cs nuclear magnetic resonance. Cs₃Bi₂Br₉was also studied by ⁸⁷Br nuclear quadrupole resonance. The parameters of the Cs electric-field gradient tensors were determined. The phase transitions were shown to produce significant changes in the nearest neighbor environment of only one of two inequivalent Cs sites. In Cs₃Sb₂I₉, the tensors remain axisymmetric below the transition at 85 K, in line with the assumption relying on powder x-ray diffraction data that, below the transition temperature, Cs₃Sb₂I₉has a trigonal structure. The observed temperature variation in the shape of the ¹³³Cs NMR and ¹²⁷I NQR signals suggests that Cs₃Bi₂I₉may undergo a transition to an incommensurate phase.     

Synthesis and Study of Sr[HSiUO6]2·2H2O and Ba[HSiUO6]2·2H2O

Uranosilicates of the general formula M^{I I}[HSiUO₆]₂·2H₂O (M^{I I} = Sr, Ba) were prepared by hydrothermal synthesis. Previously unknown intermediate crystal hydrates were separated and studied by X-ray diffraction (XRD), IR spectroscopy, and thermal analysis. Polymorphic transitions -Sr[HSiUO₆]₂ -Sr[HSiUO₆]₂ and -Ba[HSiUO₆]₂ -Ba[HSiUO₆]₂ were revealed at 700 and 780°C, respectively.     

Computer Simulation of Noncrystalline P2O5 , an Ionic–Covalent Oxide

The semiclassical molecular dynamics simulation method proposed earlier for studying ionic–covalent oxide systems was applied to noncrystalline P₂O₅. The expressions for the potentials of ionic–covalent bonds were found. The internal energy comprises the contributions from the ionization energy of phosphorus, electron affinity of oxygen, Coulombic interaction, repulsion between ionic shells, and covalent interaction. The ionic charges were computed by minimizing the potential energy at each simulation step. Taking into account mixed bonding improves agreement with the experimental data on the density, energy, and structure of condensed P₂O₅. The bond ionicity in glassy P₂O₅is about 68%. The proposed potentials are shown to be suitable for computing a number of properties of isolated P₄O₁₀molecules.     

Comparison Between γ-Bi2MoO6 and Bi2WO6 Catalysts in the CO Oxidation

Bismuth molybdate (-Bi₂MoO₆) and bismuth tungstate (Bi₂WO₆) catalysts were prepared by solid-state reaction and their catalytic properties evaluated in the CO oxidation reaction. We characterize their structure by X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and BET nitrogen absorption. X-ray diffraction analysis shows that both -Bi₂MoO₆ and Bi₂WO₆ are structural analogs (SG P2₁ ab). Auger analysis shows that Bi₂WO₆ catalysts have more bismuth on the surface than -Bi₂MoO₆, although both samples are bismuth deficient as compared to the stoichiometric compound. The results regarding catalytic activity show that Bi₂WO₆ prepared at 1073 K reaches total conversion of CO (100%) at a lower temperature when compared to -Bi₂MoO₆. It indicates that Bi₂WO₆ is a potential candidate to be used as catalyst in the CO to CO₂ oxidation.     

Synthesis of Ternary Intercalation Compounds in the Graphite–HNO3–R (R = H2SO4 , H3PO4 , CH3COOH) Systems

The reactions of stage II–IV graphite nitrates with concentrated H₂SO₄, H₃PO₄, and CH₃COOH were studied at graphite : acid weight ratios from 3 : 1 to 1 : 1. The results demonstrate that the reactions in question follow different paths. In the graphite nitrate–H₂SO₄system, the reaction decreases the stage index and yields a ternary graphite intercalation compound. The contents of intercalated HNO₃and H₂SO₄are controlled by the amount of H₂SO₄and the stage index of the parent graphite nitrate. The reaction between graphite nitrate and H₃PO₄leads to partial replacement of HNO₃by H₃PO₄, increasing the identity period without changes in the stage index. The results for the graphite nitrate–CH₃COOH system provide no direct evidence for the formation of an intercalation compound with HNO₃and CH₃COOH. It is shown that varying the nature and amount of the second intercalate species opens up possibilities for preparing oxidized graphite with controlled physicochemical properties.     

c-axis Superfluid Response and Quasiparticle Conductivity in Bi2Sr2CaCu2O8+δ and Bi2Sr2CuO6+δ

Josephson plasma resonance for underdoped Bi ₂ Sr ₂ CaCu ₂ O ₈₊ and Bi ₂ Sr ₂ CuO ₆₊ have been measured by sweeping the microwave, frequency continuously. The resonance enables us to determine the superfluid density and quasiparticle conductivity in the c-axis accurately. We show that the. superfluid response and the low energy excitations out of the condensate in the c-axis of these materials are very different from those in the ordinary Josephson multilayer tunnel junctions. The Josephson coupling energy in single layer Bi ₂ Sr ₂ CuO ₆₊ is more than 5000 times smaller than is predicted in interlayer tunneling model.     

Flux Flow Resistance and Transmittivity in Overdoped Tl2Ba2CuO6+δ

We have measured the surface resistance and transmittivity of overdoped Tl ₂ Ba ₂ CuO ₆₊ in magnetic field up to 7 T in order to investigate the unusual dc resistive transition. Introduction of columnar defects largely shifts the irreversibility line to higher field, showing that the resistive transition is caused by the melting of the vortex lattice. It is found that flux flow resistance of this compound is unusual as compared with that expected from the dc resistivity.     

Microstructure and microwave dielectric properties of MgNb2O6–ZnTa2O6 composite ceramics prepared by layered stacking method

ZnTa₂O₆/MgNb₂O₆/ZnTa₂O₆ layered ceramics with different volume fractions were designed and prepared to tailor the microwave dielectric properties of ZnTa₂O₆–MgNb₂O₆ composite ceramics. The crystal structure, microstructure and microwave dielectric properties of the composite ceramics were systematically investigated in this work. The formation of solid solutions at interface was confirmed by X-ray diffractometer. Scanning electron microscopy and energy dispersive spectroscopy were used to analysis the ionic diffusion behavior across the interface. The typical core–shell structure based on MgNb₂O₆ solid solution was clearly discerned in the composite ceramics. The ionic diffusion coefficients simulated by semi-infinite diffusion couple could give a reasonable explanation for the formation of the special structure. The tri-layered ZnTa₂O₆/MgNb₂O₆/ZnTa₂O₆ ceramic with the volume fraction of 6:1:6 had the optimum microwave dielectric properties of ε _r  = 31.98, Q × f = 82,778 GHz, and τ _f  = 0 ppm/°C, demonstrating a unique potential for low-loss microwave applications in resonators, filters and antenna substrates.