Inorganic Materials (v.52, #8)
Solid solutions of offretite, direnzoite, and ferrierite by T. N. Kol’tsova (743-754).
The three-dimensional geometric analysis carried out in this study has made it possible to clearly outline the homogeneity regions of solid solutions rich in magnesium and potassium oxides. Common elements in the structures of the zeolites (offretite, direnzoite, and ferrierite-Mg) have been identified and the factors responsible for the distinctions between their structures have been analyzed.
Keywords: zeolites; structure; solid solution
Thermoelectric properties of Sb2Te3–Bi2Te3 solid solutions prepared through melt solidification in liquids by L. D. Ivanova; L. I. Petrova; Yu. V. Granatkina; A. G. Mal’chev; I. Yu. Nikhezina; D. S. Nikulin; O. A. Raikina (755-761).
Using scanning electron and optical microscopies, we have studied the morphology of fracture surfaces and microstructure of samples of an Sb2Te3–Bi2Te3 solid solution (p-type conductivity) prepared by hot pressing and extrusion of granules produced through melt solidification in liquids. All of the samples were found to contain an additional phase in the form of a tellurium-based eutectic, and their macroscopic structure was shown to depend on the granule comminution procedure. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the samples have been measured in the range 100–700 K. We have obtained materials with the highest dimensionless thermoelectric figure of merit ZT ~ 1.0 at temperatures from 300 to 440 K.
Keywords: solid solution between bismuth and antimony tellurides; melt solidification in liquid; hot pressing; extrusion; fractographic analysis; microstructure; thermoelectric properties
Position sensitivity characteristics of n-CdSe epitaxial layers grown on mica crystals in a quasi-closed system by E. A. Senokosov; V. I. Chukita; R. A. Khamidullin; V. N. Cheban; I. N. Odin; M. V. Chukichev (762-764).
Photosensitive epitaxial n-CdSe layers with high structural perfection have been grown on mica (muscovite) crystals in a quasi-closed system. We have studied polar diagrams of sensitivity for the epitaxial n-CdSe layers on mica as four-contact position-sensitive semiconductor photodetectors. Position sensitivity characteristics of the epitaxial n-CdSe layers on mica have been determined.
Keywords: epitaxial layers; cadmium selenide; photodetectors; polar diagrams; position sensitivity
Phase equilibria and thermodynamic properties of saturated solid solutions based on the compounds BiSeI, Bi19Se27I3, and BiI3 in the Ag–Bi–Se–I system by M. V. Moroz; M. V. Prokhorenko (765-769).
We have studied phase relations in the AgI–BiI3–Se–Bi2Se3 region of the Ag–Bi–Se–I system for T ≤ 530 K and derived equations of overall potential-forming reactions involving the phases BiSeI, Bi19Se27I3, and BiI3. The reactions were brought about in electrochemical cells of the form C |Ag| Ag3GeS3I glass |D| C (where C stands for an inert (graphite) electrode, Ag and D denote the electrodes of the cell, D is a mechanical mixture of four phases in the system under investigation, and Ag3GeS3I glass is a membrane with purely ionic (Ag+) conductivity). The linear temperature dependences of EMF for the cells in the range 485–510 K were used to calculate the standard thermodynamic functions of the compounds BiSeI, Bi19Se27I3, and BiI3.
Keywords: bismuth selenides iodides; phase equilibrium; thermodynamic functions; EMF method
Magnetic phase diagram of solid solutions in the CoCr2S4–Cu0.5In0.5Cr2S4 system by T. G. Aminov; G. G. Shabunina; E. V. Busheva; V. M. Novotortsev (770-782).
The magnetic properties of CoCr2S4–Cu0.5In0.5Cr2S4 solid solutions have been studied in the temperature range 5–300 K at different ac magnetic field frequencies (100, 500, and 1000 Hz) and an amplitude of 79.6 A/m. We have determined the temperatures of the magnetic transformations in the system, identified their nature, and constructed the magnetic phase diagram of the solid solutions.
Keywords: magnetic semiconductor; spin glass; magnetic phase diagram
Influence of the chemical composition of precursors and reduction conditions on the properties of magnesiothermic tungsten powders by V. N. Kolosov; M. N. Miroshnichenko; V. M. Orlov (783-790).
We have studied tungsten powders prepared by reducing the tungsten oxide compounds WO3, MgWO4, CaWO4, and Ca3WO6 with magnesium vapor in the temperature range 700–800°C. In the case of the reduction of WO3 and MgWO4, we observed segregation of reaction products: removal of most of the forming magnesium oxide from the reaction zone. The powders prepared by reducing WO3, MgWO4, and CaWO4 consisted of α-W, whereas the reduction of Ca3WO6 at temperatures below 740°C led to the formation of both α-W and β-W. The use of tungsten precursors containing refractory oxides (MgWO4, CaWO4, and Ca3WO6) allowed us to obtain tungsten powders with specific surface areas at a level of 20 m2/g and mesoporous structures.
Keywords: MgWO4 ; CaWO4 ; Ca3WO6 ; magnesiothermic reduction; specific surface area
Mechanisms of the formation of a surface phase with the matrix composition in a Ca2Nb2O7 single crystal by Yu. Ya. Tomashpolsky; V. M. Matyuk; N. V. Sadovskaya (791-795).
We have studied the local composition and nanoscale surface morphology of a calcium niobate, Сa2Nb2O7, single crystal after thermally stimulated heterosegregation with the aim of identifying the mechanisms underlying the formation of a surface phase with the matrix composition. The identity of the compositions of the surface phase and matrix is accounted for in terms of a liquid-phase model for surface segregation, which includes diffusion, melting, and crystallization processes.
Keywords: thermally stimulated surface autosegregation; heterosegregation; chemical composition; surface phases; surface morphology
Preparation of porous materials from a leucoxene concentrate by K. L. Zanaveskin; R. V. Lukashev; A. N. Maslennikov; A. V. Terekhov; M. N. Makhin; L. N. Zanaveskin (796-801).
We have studied the effect of leaching conditions on the physicochemical characteristics of titanium dioxide-based powders prepared by leaching a leucoxene concentrate from the Yaregskoe deposit. The results demonstrate that, by varying the leucoxene concentrate leaching conditions and reducing the SiO2 content, one can obtain a porous titanium dioxide-based material with predetermined characteristics: chemical and phase compositions, specific surface area, and others.
Keywords: leucoxene; Yaregskoe deposit; titanium dioxide; rutile; porous material; leaching; hydrothermal synthesis
Phase composition and thermal conductivity of zirconia-based thermal barrier coatings by I. V. Mazilin; L. Kh. Baldaev; D. V. Drobot; E. Yu. Marchukov; N. G. Zaitsev (802-810).
Atmospheric plasma spraying of powder materials has been used to produce thermal barrier coatings (TBCs) based on ZrO2 stabilized with 7 wt % Y2O3, including coatings doped with neodymium and samarium oxides, for state-of-the-art and next-generation high-temperature gas turbine engines. Doping with neodymium and samarium oxides has been shown to reduce the thermal conductivity of the TBCs by 10–20%. At the same time, changes in the phase composition, crystal structure parameters, and microstructure of the TBCs during heat treatment at the service temperature lead to an increase in the thermal conductivity of all the coatings by 50–70%.
Keywords: thermal barrier coating; zirconia; rare-earth oxides; thermal conductivity
High-temperature heat capacity and vibrational spectra of Eu2Sn2O7 by L. T. Denisova; L. A. Irtyugo; Yu. F. Kargin; V. M. Denisov; V. V. Beletskii; A. A. Shubin (811-814).
The Eu2Sn2O7 compound has been prepared by solid-state reaction (by sequentially firing a stoichiometric mixture of Eu2O3 and SnO2 in air at 1273 and 1473 K) and its heat capacity has been determined by differential scanning calorimetry in the temperature range 370–1000 K. The heat capacity data have been used to evaluate the thermodynamic properties of europium stannate: enthalpy increment H°(T)–H°(370 K), entropy change S°(T)–S°(370 K), and reduced Gibbs energy Ф°(T). Raman spectra of Eu2Sn2O7 polycrystals with the pyrochlore structure have been measured in the range 200–1200 cm–1.
Keywords: high-temperature heat capacity; Raman spectra
Unique hyper-kagome atomic order in the noncentrosymmetric structure of Na3Ir3O8 by M. V. Talanov; V. B. Shirokov; V. M. Talanov (815-823).
The formation of a unique hyper-kagome atomic order in the structure of the ordered spinel phase Na3Ir3O8 has been analyzed in terms of the Landau theory of phase transitions. We have identified a critical six-component order parameter generating a phase transformation of the spinel parent phase to ordered P4132 (P4332) spinel-like enantiomorphs and examined the structural mechanism behind the development of hyper-kagome order and the detailed crystal chemistry of Na3Ir3O8.
Keywords: hyper-kagome order; ordered spinels; enantiomorphs; double helix
Preparation of PbGeO3 by the oxidation of Pb–Ge melts and its properties by L. T. Denisova; Yu. F. Kargin; L. A. Irtyugo; V. M. Denisov (824-827).
This paper presents experimental data on the oxidation kinetics of a liquid 65 at % Pb + 35 at % Ge alloy in air. Lead metagermanate, PbGeO3, in a glassy state has been prepared by high-temperature oxidation of the melt at 1273 K. Interaction of molten PbGeO3 with crucible materials (SnO2, Au, Pd, and Pt) has been studied by the sessile drop method. Liquid lead germanate has been shown to be highly reactive with substrates from these materials. The heat capacity of the glassy lead metagermanate obtained has been determined by differential scanning calorimetry in the temperature range 300–800 K. In the range 330–630 K, the C p (T) data for glassy PbGeO3 can be represented using the Maier–Kelley equation. Above 630 K, there is a characteristic peak due to glass crystallization processes.
Keywords: oxidation kinetics; high-temperature gravimetry
Tb3+ photoluminescence in mesoporous glasses, terbium nitrate and terbium chloride hexahydrates, and coordination compounds by V. S. Gorelik; S. N. Ivicheva; L. S. Lepnev; A. O. Litvinova (828-835).
We have compared the intensity and shape of photoluminescence spectra of Tb3+ ions in mesoporous glasses, inorganic phosphors (terbium nitrate and terbium chloride hexahydrates), and coordination compounds (terbium benzoate, terbium o-phenoxybenzoate, and terbium terephthalate). The excitation sources used were a repetitively pulsed nitrogen laser with an emission wavelength of 337 nm and cw semiconductor light-emitting diodes with wavelengths of 369 and 385 nm. It has been shown that the highest photoluminescence intensity normalized by the percentage of terbium is offered by terbium terephthalate and terbium- doped mesoporous glass. We are thus led to conclude that introducing terbium terephthalate into the pores of mesoporous photonic glass and mesoporous photonic crystals is a promising approach for obtaining efficient laser operation in the green spectral region on the 5 D 4–7 F 5 transition of the terbium ion.
Keywords: photoluminescence; mesoporous glass; phosphors; terbium; lanthanides; precursor; laser; semiconductor light-emitting diode; energy level
Phase formation and dielectric properties of lithium fluoride-doped (Na0.5Bi0.5)TiO3–(K0.5Na0.5)NbO3–BiFeO3 ceramics by G. M. Kaleva; A. V. Mosunov; E. D. Politova (836-841).
Single-phase ceramic samples in the morphotropic phase boundary region of the (1–y)[(1–x)(Na0.5Bi0.5)TiO3 ∙ x(K0.5Na0.5)NbO3] ∙ yBiFeO3 system (х = 0.06, 0.08, 0.10; y = 0.025, 0.05, 0.075, 0.10) have been prepared by solid-state reactions, and the effect of LiF as a low-melting-point additive (5 wt %) on the phase formation process and the dielectric properties of the solid solutions has been studied. The addition of LiF has been shown to activate the phase formation process and lower the sintering temperature of ceramic samples. The modification of the ceramics with lithium fluoride slightly increases the unit-cell parameters of the solid solutions. The addition of LiF lowers their Curie temperature.
Keywords: ceramic solid solutions; perovskite structure; phase formation; Curie temperature; dielectric properties; piezoelectric properties
Irradiation behavior of ytterbium-doped calcium fluoride crystals and ceramics by M. Kh. Ashurov; S. T. Boibobeva; I. Nuritdinov; E. A. Garibin; A. A. Demidenko; S. V. Kuznetsov; P. P. Fedorov (842-850).
We have studied the radiation resistance of CaF2:Yb3+ (3 mol % YbF3) laser ceramics and a single crystal of similar composition (3.6 mol % YbF3) exposed to gamma rays in a 60Co source. The unirradiated samples have been shown to be similar in spectral characteristics. Even though irradiation leads to identical valence changes, Yb3+↔Yb2+, in the single crystals and ceramics, it produces characteristic defect centers in the ceramic samples, which are responsible for the observed marked differences in the rate of valence changes and the annealing rate of radiation-induced defects.
Keywords: radiation resistance; laser ceramics; gamma rays; spectral characteristics; defects
Modification of the properties of tin sulfide films grown by spray pyrolysis by I. G. Orletskii; P. D. Maryanchuk; E. V. Maistruk; M. N. Solovan; D. P. Koziarskyi; V. V. Brus (851-857).
n-Type SnS and SnS2 sulfide films up to 0.6 μm in thickness, with resistivity in the range 2 ≤ ρ ≤ 17 kΩ cm have been grown by spray pyrolysis of aqueous solutions of the SnCl2 ∙ 2H2O, SnCl4 ∙ 5H2O, and (NH2)2CS salts at substrate temperatures in the range 523 ≤ T s ≤ 623 K. At constant thermal conditions of sulfide film growth, varying the chemical composition of the solutions for spray pyrolysis makes it possible to obtain films with substantially different optical properties. Undoped SnS and SnS2 have high transmittance, T ≈ 40–70%, and a sharp intrinsic absorption edge. The optical band gap of the SnS and SnS2 sulfide films has been shown to depend on film growth conditions.
Keywords: spray pyrolysis; SnS; SnS2 ; thin films; electrical properties; optical properties
Stable suspensions of doped ceria nanopowders for electrophoretic deposition of coatings for solid oxide fuel cells by E. G. Kalinina; O. M. Samatov; A. P. Safronov (858-864).
We have studied nonaqueous suspensions of Ce0.8Sm0.2O1.9 (CSO), Ce0.8Gd0.2O1.9 (CGO), and Се0.8(Sm0.75Sr0.2Ba0.05)0.2O2–δ (CSSBO) nanopowders produced by laser evaporation of a target. The nanoparticles were nearly spherical in shape and their average diameter was 9, 7, and 15 nm, respectively. Using ultrasonic processing, we obtained stable nanopowder suspensions in an isopropanol + acetylacetone mixed medium, investigated their particle size composition, evaluated their zeta potential as a function of pH, and obtained potentiometric titration curves. The starting nanopowder suspensions have been shown to be weakly acidic and have a rather high initial zeta potential. During titration of the nanopowder suspensions with 0.17 N KOH in isopropanol, no isoelectric point was observed. The maximum positive values of the zeta potential, favorable for electrophoretic deposition (EPD), were reached in weakly acidic media in the pH range 4–6. Using EPD, we obtained a coating from a stable self-stabilized CSSBO suspension (ζ = +31 mV, pH 4.0), which was then sintered in air at a temperature of 1400°C. Our results demonstrate that the starting nonaqueous suspensions of the CSO, CGO, and CSSBO nanopowders suit well for producing gas-tight, homogeneous solid oxide fuel cell coatings by EPD.
Keywords: nanopowders; zeta potential; electrophoretic deposition