Inorganic Materials (v.53, #7)

A physicochemical study of the Sb2Se3–Nd2Se3 system by F. M. Sadygov; T. M. Il’yasly; G. T. Ganbarova; V. P. Zlomanov; I. I. Aliev (665-669).
We have studied phase relations in the Sb2Se3–Nd2Se3 system and mapped out its Tx phase diagram using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements. The system contains one compound, with the composition NdSbSe3, which melts incongruently at 865 K and crystallizes in orthorhombic symmetry with the following lattice parameters: а = 12.77(1) Å, b = 14.08(1) Å, and c = 5.82(5) Å (Z = 8, ρmeas = 6.20 g/cm3, ρx = 6.38 g/cm3). At room temperature, the Nd2Se3 solubility in Sb2Se3 is 5 mol % and the Sb2Se3 solubility in Nd2Se3 is 2.5 mol %. The Sb2Se3–Nd2Se3 system has a eutectic located at 15 mol % Nd2Se3, with a melting point at 755 K. The electrical conductivity and thermoelectric power of the (Sb2Se3)1–x (Nd2Se3) x solid solutions have been measured as functions of temperature.
Keywords: Sb2Se3–Nd2Se3 system; NdSbSe3 compound; eutectic; electrical conductivity; crystal system

Crystal structure and electronic spectrum of InGaSe2 by E. M. Gojaev; Z. A. Jakhangirli; R. S. Ragimov; P. F. Alieva (670-674).
We report the synthesis and crystal growth of InGaSe2. The crystals have been characterized by X-ray diffraction and InGaSe2 has been shown to crystallize in tetragonal symmetry. Using first-principles density functional theory (DFT) calculations, we have found optimized lattice parameters and equilibrium atomic position coordinates of the compound semiconductor InGaSe2. Based on the optimization results, we have calculated the band structure and the total and projected densities of states in InGaSe2, found out the origin of its conduction and valence bands, and determined its band gap. Using the partial densities of states of its constituent atoms, we have evaluated the nature of the chemical bonding in InGaSe2.
Keywords: InGaSe2 ; X-ray diffraction; DFT; band structure

The Hall coefficient, resistivity, and thermoelectric power of quaternary tetradymite-like layered materials in the pseudoternary system Sb2Te3–GeTe–Bi2Te3 have been measured in the temperature range 100–800 K. The results demonstrate that all of the samples studied in the Sb2Te3–GeTe–Bi2Te3 system are p-type and have high hole concentration due to point defects. Plots of lnσ against 1/T in the intrinsic region were used to evaluate the band gap (ΔE) of two materials: GeSb3.91Bi0.03Te6.91E = 0.22 eV) and GeSbBiTe4E = 0.197 eV).
Keywords: electrical conductivity; thermoelectric power; thermal conductivity; thermoelectric figure of merit; Hall effect

Thin polycrystalline TbSb films have been grown by thermal evaporation in vacuum from two separate sources on glass-ceramic, sapphire, and single-crystal silicon substrates. The substrate material has been shown to have no significant effect on the phase composition and crystallinity of the films. The optimal substrate temperature is 1120–1145 K. The films have a cubic structure (NaCl type), their composition is 49 ± 0.01 at % Tb + 50.1 ± 0.01 at % Sb, and their components are uniformly distributed both on the surface and in the bulk of the films. The resistivity, Hall coefficient, and thermoelectric power of the films have been measured as functions of temperature in the temperature range 95–700 K. It has been shown that charge carriers in the films are electrons, with a concentration of ~1026 m–3 and mobility of ~10–3 m2/(V s). According to the electrical measurements, TbSb is a semimetal.
Keywords: film; electrical resistance; Hall coefficient; thermoelectric power; semimetal

Phase equilibria in the Tl5Te3–Tl9BiTe6–Tl9TbTe6 system by S. Z. Imamaliyeva; T. M. Gasanly; V. P. Zlomanov; M. B. Babanly (685-689).
Phase equilibria in the Tl5Te3–Tl9BiTe6–Tl9TbTe6 system have been studied using differential thermal analysis, X-ray diffraction, and microhardness measurements. We have mapped out a number of vertical sections, the 760-K isothermal section of its phase diagram, and projections of its liquidus and solidus surfaces. The composition dependences of lattice parameters and microhardness have been obtained. The system has been shown to contain a continuous series of solid solutions, which crystallize in a tetragonal structure (Tl5Te3 type, sp. gr. I4/mcm).
Keywords: thallium tellurides; terbium tellurides; thallium bismuth tellurides; phase equilibria; liquidus surface; solid solutions; crystal lattice

We have studied the effect of tungsten, molybdenum, and hafnium concentrations on the electrical conductivity, nanohardness, and elastic modulus of metal-containing silicon–carbon nanocomposite films. The results demonstrate that the addition of these metals to the films leads to the formation of metal carbide particles a few nanometers in size. At metal contents from 5 to 35 at %, the conductivity of the films varies over four orders of magnitude (from 10–1 to 103 S/cm). The composition dependences of the mechanical properties of the nanocomposites depend on the nature of the metal. We have analyzed the mechanisms underlying the effect of the metals on these properties.
Keywords: electrical conductivity; nanohardness; elastic modulus

We have prepared chemically homogeneous Mn5Ge3 single crystals and evaluated the anisotropy in their electrical resistivity and linear expansion coefficient. These properties have been shown to vary anomalously with temperature near the ferromagnetic transition of Mn5Ge3. In the temperature range 320–900 K, its resistivity remains constant.
Keywords: anisotropy; electrical resistivity; linear expansion; germanides

Melting behavior of the Nowotny phase Mo4.8Si3C0.6 by B. A. Gnesin; I. B. Gnesin (701-707).
Mixtures of the Mo5Si3 silicide with 1.1–2.4 wt % carbon were melted after reaction sintering and the formation of the Nowotny phase (Mo4.8Si3C0.6), and the effect of various heat treatments on the phase composition of the samples was studied. The crystallization of the melted samples leads to a reduction of the volume fraction of the Nowotny phase relative to that after reaction sintering, but subsequent annealing below the liquid phase formation temperature allows the volume fraction of Mo4.8Si3C0.6 to be again raised. We discuss possible causes of the observed phase transformations.
Keywords: Nowotny phase; silicides; phase equilibrium; high-temperature materials

Thermal hysteresis of electromechanical characteristics of Y + 42° cut LiTaO3 single crystals by M. N. Palatnikov; V. A. Sandler; N. V. Sidorov; O. V. Makarova (708-712).
The temperature stability of electromechanical characteristics of Y + 42° cut LiTaO3 crystals has been studied using dielectric spectroscopy and static and dynamic piezoelectric effect measurements. It has been shown that, during thermal cycling, the piezoelectric properties of crystalline LiTaO3 samples exhibit a thermal hysteresis and that the thermal history of samples influences their resonance and antiresonance frequencies.
Keywords: crystals; lithium tantalate; piezoelectric modulus; piezoelectric resonance; residual strain; anisotropic; thermal cycling

Analysis of IR absorption spectra of LiNbO3:Zn (0.04–4.46 mol % ZnO) and LiNbO3:Mg (0.19–5.91 mol % MgO) single crystals in the stretching region of OH groups has been used to gain insight into composition-dependent structural changes in the crystals. The results demonstrate that, characteristically, the OH groups occupy different sites in the doped and congruent LiNbO3 crystals and have different quasielastic O–H bond constants in their structure. In stoichiometric lithium niobate crystals, all of the OH sites and quasi-elastic O–H bond constants are identical. At threshold Zn and Mg dopant concentrations, the frequencies, widths, and intensities of the observed lines change sharply. The linewidths in the spectra of the LiNbO3:Zn crystals near their first concentration threshold (≈2.0 mol % ZnO) and the LiNbO3:Mg crystals near their first and second concentration thresholds (≈3.0 and 5.5 mol % MgO) decrease markedly, indicating ordering of the position of the OH groups in the structure of the crystals.
Keywords: Fourier transform infrared spectroscopy; vibrational spectra; absorption spectra; phonon frequency; stretching vibrations; nonlinear optical crystals; doping

The mixing energies (interaction parameters) of solid solutions in orthophosphates La1–x Ln x PO4 of rare earth elements (REE) with monazite structure are calculated within the framework of the crystal energy theory of isomorphous replacement. Their values and contributions to the mixing energy depending on the size of replaceable structural units and the degree of ionicity of the chemical bond within the row of lanthanides from Ce to Dy expectedly increase. Accordingly, there is an increase in critical temperatures of solid solution decomposition (stability). This agrees with the previous results of ab initio quantum chemical calculations.
Keywords: solid solution; orthophosphate; mixing energy calculation

The studied samples ZnMoO4–MoO3, have been prepared by immersing an amount of molybdenum oxide in zinc acetate solution according to the appropriate molar ratio x = ZnO/MoO3 = 0, 0.2, 0.4, 0.6, 0.8 and 1. These samples were then heated at temperature of 500°C for 3 hours. Prepared samples were characterized using different techniques such as: X-ray diffraction, Fourier spectroscopy, Raman spectroscopy, differential thermal analysis and nitrogen adsorption-desorption measurements. The Photocatalytic activity was studied via degradation of methyl red in aqueous solution when subjected to UV radiation. The results of this work revealed some variations, by increasing ZnO quantity, in phase composition and textural characteristics of ZnMoO4–MoO3 samples. It was found that these changes affect the photocatalytic activity by enhancing the degradation rate of Methyl red during the UV irradiation process.
Keywords: MoO3 ; ZnMoO4 ; composites; photocatalyst; Methyl red

Thermodynamic properties of GdTaO4 by M. A. Ryumin; E. G. Sazonov; V. N. Guskov; P. G. Gagarin; A. V. Khoroshilov; A. V. Guskov; K. S. Gavrichev; L. Kh. Baldaev; I. V. Mazilin; L. N. Golushina (728-733).
The heat capacity of monoclinic gadolinium orthotantalate has been determined as a function of temperature by adiabatic and differential scanning calorimetry in the temperature range 8–1323 K. Smoothed heat capacity data have been used to calculate the thermodynamic functions of M-GdTaO4 with allowance for the contribution of its low-temperature magnetic transformations.
Keywords: adiabatic calorimetry; thermodynamic properties; gadolinium orthotantalate

Dielectric properties of crystals of (Pb1–x Ba x )5Ge3O11 solid solutions by A. V. Stepanov; A. A. Bush; K. E. Kamentsev (734-740).
Crystals of (Pb1–x Ba x )5Ge3O11 (0 ≤ x < 0.12) ferroelectric solid solutions have been grown via slow melt cooling and characterized by X-ray diffraction and dielectric measurements. The results demonstrate that the partial Ba substitution for Pb atoms in the crystals leads to a monotonic increase in their hexagonal cell parameters and a rather drastic degradation of their ferroelectric properties: a decrease in their Curie temperature T C from 450 to 120 K and a decrease and broadening of the peaks in their dielectric permittivity εmax and dielectric loss tangent tan δmax at T C. In addition to the dielectric anomalies near T C, the dielectric properties of the crystals demonstrate features of relaxation character in the ranges 220–260 and 20–170 K. Starting in the composition range x = 0.06–0.08, εmax increases with Ba content, instead of decreasing. Moreover, in this composition range the dielectric properties of the crystals depend markedly on their thermal history. The observed anomalies in the temperature and composition dependences of the dielectric properties of the solid solutions have been interpreted in terms of the dynamics of the thermal localization of charge carriers at defect levels with ionization energies Ua1 ≈ 0.6 eV and Ua2 ≈ 0.2 eV, as well as at shallower levels, in the temperature range 240–280 K and below 160 K, respectively, and the shift of T C to these temperature ranges with increasing Ba content.
Keywords: lead barium germanate; ferroelectric solid solutions; dielectric properties

This paper presents a three-dimensional geometric analysis of the homogeneity regions of gismondine, cymrite, anorthite, and celsian solid solutions with the use of two composition tetrahedra: AO–BO0.5–AlO1.5–SiO2 and AO–AlO1.5–SiO2–H2O (where A = alkaline-earth element and B = alkali element). The main general aspects of the extension of the homogeneity regions are elucidated. The position of the homogeneity regions in the composition tetrahedra suggests that increasing the percentage of SiO2 should lead to a gismondine–cowlesite phase transition and that a few phase transitions should be expected in the course of gismondine dehydration, which will lead to the formation of a solid solution with the anorthite structure after all of the water will be removed.
Keywords: zeolites; feldspars; solid solution

Heterophase conversion of K2ZrF6 into zirconium hydroxide by A. V. Zhukov; S. V. Chizhevskaya; Pyae Phyo (752-757).
We have studied general kinetic aspects of the heterophase conversion of single-phase potassium hexafluorozirconate into zirconium hydroxide by potassium hydroxide solutions, related to the influence of the alkali concentration, the alkali-to-K2ZrF6 molar ratio, and temperature. The synthesized crystal-like X-ray amorphous zirconium hydroxide is an anamorphosis of potassium hexafluorozirconate. Heat treatment of the hydroxide at a relatively low temperature leads to the formation of nanostructured metastable tetragonal zirconium dioxide.
Keywords: heterophase conversion; zirconium hydroxide; nanostructured ZrO2

This paper describes a mathematical model for the behavior of impurity nanoparticles in two flowing contacting melts which takes into account the surface tension forces on the interface between the melts. The nanoparticle distribution in a bilayer cylindrical melt flow is shown to be significantly influenced by the diffusion mechanism and surface tension forces. The proposed calculation procedure is applied to As40S60–As35S65 (core–cladding) glasses and silica nanoparticles.
Keywords: impurity nanoparticles; interface; surface tension forces; computer simulation; chalcogenide fibers

Phase formation, microstructure, and ionic conductivity of (La,Sr)(Ga,Ge,Mg)O3–d ceramics by G. M. Kaleva; A. V. Mosunov; N. V. Sadovskaya; E. D. Politova (764-769).
We have prepared ceramic (La0.8Sr0.2){[Ga0.8–x (Ge0.5Mg0.5) x ]Mg0.2}O3–d (LSGGM) (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8) samples by solid-state reactions and studied their phase composition, structure, microstructure, and electrical conductivity. Phase-pure solid solutions have been obtained upon substitution of germanium and magnesium cations for up to 20 at % of the gallium cations. The modified samples have been shown to have high density, optimal microstructure, densely packed grains, and high electrical conductivity at high temperatures.
Keywords: ion-conducting ceramics; lanthanum gallate; perovskite structure; phase formation; microstructure; electrical conductivity

Model for the calculation of the volume change on melting of metals by V. N. Chuvil’deev; A. V. Semenycheva (770-773).
A phenomenological model has been proposed that allows the volume change on melting of metals to be related to the valence, thermodynamic properties, and crystallographic parameters of the solid phase. Basic to the model are ideas that a phonon “analog of the Casimir force” plays a key role in determining the metal melting process.
Keywords: first-order phase transition; Casimir force; crystallization