Vol 53, No 6 (2017)

Spray pyrolysis of aqueous solutions, with thiourea as a sulfurizing agent, has been used to grow cubic indium sulfide films on single-crystal substrates: In_3–xS₄(111)/Si(100), In_3–xS₄(111)/GaAs(100), and In_3–xS₄(111)/InP(100). The lattice parameter a of the sulfide has been shown to increase with an increase in the lattice parameter of the substrate, whereas the film grown on GaAs has the highest lattice strain (as assessed from X-ray diffraction line broadening). The films have a constant phase composition and (111) texture, in contrast to films grown on glassy substrates by the same method.

We have carried out a comparative study of the electrical properties of lithium tantalate (LiTaO₃) crystals in a wide temperature range (300–900 K) before and after reductive treatment in H₂O vapor and subsequent oxidative annealing. The results demonstrate that, in the temperature range of Li⁺ ion conduction (550–900 K), the activation enthalpy for ionic conduction in the reduced lithium tantalate crystal is H_a = 1.37 eV, which slightly exceeds that in the initial state of the crystal (1.34 eV). In the temperature range 390–450 K, the σ(T) data for the unannealed crystal are well represented by the Arrhenius law in the presence of two carrier types, with activation energies E₁ = 1.03 eV and E₂ = 0.29 eV, characteristic of proton and electron hopping conduction, respectively. After reductive annealing, the activation energy for conduction is ~0.65 eV, characteristic of the activation energy for bipolaron conduction. After subsequent oxidative annealing of the reduced crystals in dry air, the activation energy is ~1.2 eV. It seems likely that the presence of oxygen vacancies in the reduced LiTaO₃ crystal stimulates hydrogen release from the crystal during oxidative annealing.

The electrical conductivity (σ) of Ca_1–xPr_xMnO_3–δ (х = 0–0.15) manganites with a perovskite-like structure has been measured by the four probe method in air at temperatures (T) from 320 to 1220 K. The results have been analyzed in terms of a model of small adiabatic polarons. The observed decrease in σ with increasing T is primarily due to the decrease in carrier concentration as a result of Mn³⁺ disproportionation into Mn²⁺ and Mn⁴⁺. The polaron mobility ranges from 0.2 to 1.2 cm²/(V s) and decreases with increasing praseodymium content.

The surface morphology and composition of MoO₂ prepared via the low-temperature decomposition of a molybdenum(VI) isopropylhydroxylaminate complex, MoO₂(i-C₃H₇NHO)₂, have been studied by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). During the sample preparation process for XPS, the molybdenum dioxide, which has the form of nanocrystals, actively reacts with atmospheric oxygen and moisture because of the small particle size of the material. The composition of the surface layer in terms of molybdenum is 5 at % MoO₂, 10 at % Mo₂O₅, and 85 at % MoO₃, and the E_b(Mo 3d_5/2) binding energy is 230.0, 231.4, and 233.1 eV, respectively. After argon ion etching of the sample surface for 45 s, the surface composition is 52 at % MoO₂, 23 at % Mo₂O₅, and 25 at % MoO₃. In addition, there are ~3 carbon atoms per Mo atom. Based on analysis of the structure of the C 2s, 2p valence electron spectra, we assume that the carbon on the sample surface is present as amorphous or nanoparticulate carbon phases. The material studied here does not become charged when exposed to an X-ray beam, which suggests that it is a weak dielectric.

The isobaric heat capacity of p-Sm₂Zr₂O₇ (pyrochlore phase) has been determined in the temperature range 10–1400 K using adiabatic, differential scanning, and relaxation calorimetry, and its enthalpy increment, entropy, and reduced Gibbs energy have been calculated with allowance for the contributions of its low-temperature magnetic transformations.

This paper discusses correlations in the impurity composition of the purest solid group 13–16 elemental substances so far, exemplified by a set of samples in the Exhibition–Collection of Extrapure Substances, a permanent exhibition. The abundance of particular elemental impurities in the samples of the high-purity substances has been determined. Dividing the entire set of impurities into classes, we have accurately determined integral characteristics (average and total concentrations) of impurities in the samples and evaluated the contribution of each impurity class to the total impurity concentration.

We have calculated the impurity distribution in a spherical material during sublimation. The solutions found depend on two dimensionless parameters: separation factor β and diffusional Peclet number Pe = wR₀/(ρ₁D), where w is the mass vaporization rate, R₀ is the initial sphere radius, ρ₁ is the density of the material, and D is the impurity diffusion coefficient. For the limiting cases Pe ≫ 1 and Pe < 1, we derived analytical expressions for the impurity distribution in the subliming material and for the average impurity concentrations in the residue and condensate as functions of time t or the degree of sublimation g(t). The present results can be used to optimize the dimensions of subliming materials and sublimation conditions.

Spark plasma sintering is widely used for the fast sintering of powders under controlled grain growth conditions and for simultaneous sintering of compounds and consolidation of powder materials. Spark plasma sintering facilities can be used as well for heat-treating powders and compact materials. In this study, an assembly without the upper punch has been used for heat treatment. It has been shown that annealing results depend on geometric features of the position of the sample in the graphite die. In a layer of a material heat-treated in a die without its upper punch, graded structures can be obtained. An example of the annealing of detonation coatings demonstrates the possibility of producing layers on substrates with compositions similar to those of compact materials produced by the spark plasma sintering of the starting powders.