Inorganic Materials (v.54, #1)

This paper presents spatial structure optimization results and calculated electronic spectra for ZrGe n (n = 8–20) anion clusters. Comparison of density-functional calculation results and available experimental data allows us to identify real spatial structures of the clusters. The formation of stable endohedral ZrGe n clusters is possible for n ≥ 12. The clusters with a smaller number of germanium atoms predominantly have exohedral structures.
Keywords: spatial structure; density functional theory; ZrGe n clusters

Phase Equilibria in the Cu2Se–Cu3AsSe4–Se System and Thermodynamic Properties of Cu3AsSe4 by L. F. Mashadieva; Z. T. Gasanova; Yu. A. Yusibov; M. B. Babanly (8-16).
The Cu2Se–Cu3AsSe4–Se system has been studied using differential thermal analysis, X-ray diffraction, and emf measurements on concentration cells using Cu4RbCl3I2 as a solid electrolyte. We have constructed a number of vertical sections through the phase diagram, the room-temperature solid-state phase compatibility diagram, and a projection of the liquidus surface. The primary crystallization fields of the phases present and the types and coordinates of in- and univariant equilibria in the system have been identified. The system has been shown to contain a broad liquid–liquid immiscibility region. Using emf data, we evaluated the standard thermodynamic functions of formation and standard entropy of the Cu3AsSe4 compound.
Keywords: Cu–As–Se system; phase diagram; liquidus surface; copper arsenic selenides; Cu3AsSe4 compound; thermodynamic properties

The thermoelectric properties of layered compounds and solid solutions in the Sb2Te3–PbTe–Bi2Te3 system have been studied in a wide temperature range. The quaternary compounds and multicomponent solid solutions in this system have been shown to have a very low lattice thermal conductivity. The electrical conductivity of all the materials decreases with increasing temperature. All of the materials have been shown to be n-type. The layered compounds and multicomponent solid solutions have high thermoelectric efficiency, which makes them promising n-type thermoelectric materials.
Keywords: electrical conductivity; thermoelectric power; thermal conductivity; thermoelectric figure of merit; Hall effect

Effect of Annealing Atmosphere on Chromium Diffusion in CVD ZnSe by S. A. Rodin; E. M. Gavrishchuk; V. B. Ikonnikov; D. V. Savin (21-25).
This paper examines the effect of high-temperature doping conditions on Cr2+ diffusion in polycrystalline zinc selenide. The activation energy for the diffusion process is determined in the temperature range 900–1100°C for annealing in an argon atmosphere and zinc vapor, and the mechanism responsible for the enhanced chromium diffusion in the case of doping in zinc vapor is discussed.
Keywords: crystal growth; zinc chalcogenide; diffusion

Effect of Gallium Nitride Film Growth Conditions on Surface Segregation by Yu. Ya. Tomashpolsky; V. M. Matyuk; N. V. Sadovskaya (26-31).
The micro-and nanomorphology and local composition of gallium nitride (GaN) films produced by four different procedures have been studied with the aim of detecting autosegregation phenomena. As a result, a complex autosegregation picture has been demonstrated and discussed. Independent of the growth procedure, all of the gallium nitride films have nonstoichiometric chemical compositions (gallium deficiency), with a degree of nonstoichiometry ranging from ~0.30 to <0.10. We discuss the segregation mechanism, which presumably involves predominant selective diffusion of nitrogen atoms to the surface.
Keywords: surface segregation; gallium nitride films; chemical composition; nonstoichiometry; surface gallium deficiency

Thermomigration Kinetics in the Si–Al–Ga and Si–Al–Sn Systems by V. V. Kuznetsov; V. N. Lozovskii; V. P. Popov; E. R. Rubtsov; B. M. Seredin (32-36).
The thermodynamics and kinetics of the thermomigration of molten zones based on Al–Ga and Al–Ga melts in the preparation of silicon epilayers have been studied in detail. We have determined the threshold thermomigration temperature for zones of various compositions. The migration onset temperature has been shown to increase monotonically with increasing Ga or Sn concentration in the liquid phase. The thermomigration rate of Si–Al–Ga zones decreases with increasing gallium concentration at temperatures below 1473 K and increases at higher temperatures. The thermomigration rate of Si–Al–Sn zones decreases with increasing Sn concentration over the entire temperature range studied. No chemical compounds have been detected in the Si–Al–Ga or Si–Al–Sn system, which simplifies the use of the thermomigration method in these systems.
Keywords: thermomigration; molten zone; melt; phase diagram

Structural and Phase Transformations in Alloys during Spark Plasma Sintering of Ti + 23.5 at % Al + 21 at % Nb Powder Mixtures by B. K. Karakozov; M. K. Skakov; Sh. R. Kurbanbekov; V. V. Baklanov; A. A. Sitnikov; D. V. Dudina; V. I. Maly; V. I. Yakovlev (37-41).
We have studied the effect of sintering temperature on the structural and phase transformations of alloys produced by the spark plasma sintering of Ti + 23.5 at % Al + 21 at % Nb powder mixtures at temperatures in the range 1100–1550°C. The sintered alloys have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy (elemental X-ray mapping). The alloys sintered at temperatures of 1100 and 1200°C have been shown to have a nonuniform microstructure. According to electron microscopy results, the alloys consist of grains of the α2 and Nb2Al phases and small precipitates of the O-phase (intermetallic compound Ti2AlNb). In addition, there are particles of unreacted niobium and titanium. The alloys sintered at a temperature of 1300°C have a uniform lamellar structure.
Keywords: intermetallic compound; titanium aluminide; spark plasma sintering; microstructure

Interaction of R1 – x Zr x Si (R = La, Ce, Nd, Dy; x = 0–0.05) Silicides with Hydrogen by S. A. Lushnikov; E. A. Movlaev; V. N. Verbetsky (42-44).
The interaction of R1 – x Zr x (R = La, Ce, Nd, Dy; x = 0–0.05) silicides with hydrogen has been studied at hydrogen pressures of up to 250 MPa. At a high pressure and a temperature of 20°C, hydrogen solubility in the solid phase is very low. Raising the reaction temperature leads to disproportionation of the silicides. According to X-ray diffraction data, the disproportionation reaction yields a rare-earth hydride and RSi2 disilicide.
Keywords: rare-earth silicides; hydrogen; hydrides; high pressure

X-Ray Photoelectron Spectra of TbB66 by Yu. M. Shul’ga; E. N. Kabachkov; P. V. Fursikov; S. A. Mironova; S. P. Shilkin; B. I. Kornev; V. V. Novikov (45-48).
Polycrystalline TbB66 has been characterized by X-ray photoelectron spectroscopy. The surface layer of TbB66 has been shown to be substantially enriched in terbium. Moreover, the surface layer of TbB66 contains boron ions having a negatively charge whose magnitude exceeds that in the case of the reference compound TbB4.
Keywords: terbium borides; X-ray photoelectron spectra; magnetic susceptibility; X-ray diffraction

Structure and Properties of Boron-Doped LiNbO3 Single Crystals by O. V. Makarova; M. N. Palatnikov; I. V. Biryukova; N. A. Teplyakova; N. V. Sidorov (49-54).
We have studied the macro-and microstructure and properties of LiNbO3〈B〉 crystals in comparison with LiNbO3〈Zn〉 and stoichiometric and congruent lithium niobate crystals. The optical characteristics of the LiNbO3〈B〉 crystals have been shown to approach those of the stoichiometric LiNbO3 and LiNbO3〈Zn〉 crystals.
Keywords: crystal; lithium niobate; doping; optical microscopy; spectroscopy

The radiation hardness and optical characteristics of beta-and gamma-irradiated LiNbO3〈ZnO〉 crystals have been studied in a wide range of doping levels: ~0.04–5.9 mol % ZnO. The optical absorption (transmission) of the beta-and gamma-irradiated LiNbO3〈ZnO〉 crystals has been evaluated as a function of the type and dose of radiation and dopant concentration. The optical damage resistance and radiation hardness of the crystals have been shown to be interrelated and depend on threshold effects in the LiNbO3〈ZnO〉 crystals.
Keywords: crystals; lithium niobate; doping; beta and gamma irradiation; optical absorption; radiation hardness

Vanadium oxide-based nanomaterials have been prepared by cryochemical synthesis (CCS) and supercritical drying (SCD) in n-hexane and acetone. We have performed the first comparative analysis which demonstrates differences in the physicochemical and electrochemical properties of the products, related to the key features of the effect of the CCS and SCD approaches. The nanomaterials prepared from the same precursor using CCS and SCD (in acetone and n-hexane) have been shown to differ in phase composition and morphology. The oxidizing annealing of the resultant aerogels and cryogel at 500°C in air leads to the formation of only one phase: α-V2O5. In all cases except the aerogel prepared using SCD in n-hexane, the crystalline α-V2O5 has a higher discharge capacity in comparison with the unannealed aerogels and cryogel. The highest discharge capacity among the annealed aerogels is offered by the sample prepared using SCD in acetone (255 mAh/g), and the highest discharge capacity among the unannealed materials is offered by the sample prepared using SCD in n-hexane (280 mAh/g). The samples range in energy density from 110 to 640 Wh/kg. The highest energy density is also offered by the aerogel prepared using SCD in n-hexane.
Keywords: lithium ion batteries; cathode; aerogel; vanadium oxides; supercritical drying; cryochemical synthesis

The dissolution of manganese oxides in sulfuric acid solutions of various concentrations has been studied by kinetic methods. We have investigated the dissolution of manganese oxides of various compositions in sulfuric acid solutions of various concentrations. The composition of the manganese oxides and the sulfuric acid concentration have been shown to influence the dissolution rate. We have calculated kinetic parameters of the dissolution of manganese oxides in sulfuric acid solutions (dissolution rate, activation energy for dissolution, and reaction orders) and proposed a model for the dissolution of manganese oxides in sulfuric acid solutions.
Keywords: sulfuric acid (H2SO4); disproportionation; rate equation for heterogeneous reactions; process steps; mathematical model of a process; activation energy; manganese oxides (MnO, Mn3O4, Mn2O3, MnO2); dissolution rate

Barium titanyl oxalate (BTO) with small deviations from stoichiometry has been synthesized by a chemical and a sonochemical method (under ultrasonication). Ultrasonic processing has been shown to reduce the particle size of the resultant BTO powder by about ten times and ensure a nearly spherical shape of the particles. The morphology of barium titanate powders prepared by decomposing the BTO at a temperature of 900°C is similar to that of the parent BTO and independent of stoichiometry. The powders have a barium to titanium ratio Ba/Ti = 1.002 and 0.987. The barium titanate powders synthesized using the sonochemical method contain a smaller amount of residual phases and have a larger specific surface area, smaller crystallite size (~100 nm), and smaller unit-cell parameters than do the powders prepared without ultrasonication.
Keywords: ultrasound; powders; barium titanyl oxalate; barium titanate

Preparation and Characterization of Nanoceramics for Solid Oxide Fuel Cells by L. V. Morozova; M. V. Kalinina; I. A. Drozdova; O. A. Shilova (79-86).
Precursor powders in the ZrO2–HfO2–Y2O3–CeO2, In2O3–ZrO2, and NiO–Nd2O3 systems for components of solid oxide fuel cells have been prepared by liquid-phase synthesis. We have determined formation conditions and the particle size of ZrO2- and In2O3-based solid solutions and neodymium nickelate (Nd2NiO4), demonstrated the feasibility of producing nanocrystalline powders (10–30 nm) of tailored chemical composition in the temperature range 500–900°C, and optimized powder consolidation conditions. Nanoceramics with a crystallite size from 60 to 90 nm have been obtained and their microstructure and phase composition have been investigated. We have studied the electrical properties of the ZrO2- and In2O3-based solid solutions and the Nd2NiO4 compound and established the range of their electrical conductivity at temperatures from 300 to 1000°C: 2.27 × 10–3 to 2.51 S/cm for the ZrO2-based solid solution, 8.91 × 101 to 6.59 × 103 S/cm for the In2O3-based solid solution, and 3.98 × 102 to 5.02 × 102 S/cm for Nd2NiO4.
Keywords: zirconia; indium oxide; solid solutions; neodymium nickelate; nanocrystalline powders; consolidation; ceramics; electrical conductivity

Preparation of β-Ca3(PO4)2/Poly(D,L-lactide) and β-Ca3(PO4)2/Poly(ε-caprolactone) Biocomposite Implants for Bone Substitution by D. M. Zuev; E. S. Klimashina; P. V. Evdokimov; Ya. Yu. Filippov; V. I. Putlyaev (87-95).
Highly permeable macroporous implants of various architectures for bone grafting have been fabricated by thermal extrusion 3D printing using highly filled β-Ca3(PO4)2/poly(D,L-lactide) (degree of filling up to 70 wt %) and β-Ca3(PO4)2/poly(ε-caprolactone) (degree of filling up to 70 wt %) composite filaments. To modify the surface of the composite macroporous implants with the aim of improving their wettability by saline solutions, we have proposed exposing them to a cathode discharge plasma (2.5 W, air as plasma gas) in combination with subsequent etching in a 0.5 M citric acid solution. It has been shown that the main contribution to changes in the wettability (contact angle) of the composites is made by the changes produced in their surface morphology by etching in a low-temperature plasma and citric acid. An alternative approach to surface modification of the composites is to produce a carbonate hydroxyapatite layer via precipitation from a simulated body fluid solution a factor of 5 supersaturated relative to its natural analog (5xSBF).
Keywords: 3D printing; bioresorbable materials; composites; tricalcium phosphate; thermal extrusion; plasma processing; surface hydrophilicity

This paper analyzes results obtained in studies of K/W/Mn/SiO2 composite catalysts for the oxidative coupling of methane (OCM) and examines phase transformations involving melts that form in the K2O–WO3–Mn2O3–SiO2 system at typical temperatures of the heterogeneous OCM process.
Keywords: phase transformations; multicomponent systems; oxide composites; catalysts