Inorganic Materials (v.49, #9)

A microstructural study of a quenched InSb ingot by V. P. Sanygin; N. N. Lobanov; O. N. Pashkova; A. D. Izotov (857-861).
Samples cut from a quenched ingot of the compound semiconductor InSb have been characterized by precision X-ray diffraction. The results show that the central and top parts of the ingot have [110] texture, whereas its bottom part is polycrystalline, which is interpreted in terms of the heat removal geometry during quenching. The texture plane coincides with the easy cleavage plane (110), typical of the III–V compound semiconductors and due to dislocation pile-ups. The microstructure of the quenched InSb ingot includes characteristic microcracks, dotted with dislocation outcrops on the polished surface. The observed increase in the unit-cell parameters of quenched InSb is tentatively attributed to the high dislocation density in the quenched ingot.

Photoluminescence of Ca(Ba)Ga2S4:RE poly- and nanocrystals by A. N. Georgobiani; B. G. Tagiev; A. M. Pashaev; O. B. Tagiev; S. A. Abushov; Kh. B. Gambarova; I. Kh. Mamedov; R. A. Abdulkheiov (862-866).
The photoluminescence and photoluminescence excitation spectra and luminescence decay kinetics of CaGa2S4:Eu2+ bulk crystals and powders ranging in particle size from 100 to 600 nm have been studied in the temperature range 77–300 K. The results indicate that the full width at half maximum of the photoluminescence band of the CaGa2S4:Eu2+ nanopowders is about twice that of the bulk crystals. Analysis of the photoluminescence spectra shows that the energy position of the emission band is almost independent of the particle size, temperature, and excitation intensity in the ranges 77–300 K and 10−3 to 106 W/cm2, respectively. The shape of the photoluminescence band is well represented by a Gaussian. The excited state lifetime of the Eu2+ ion is ∼1000 ns as evaluated from the exponential portion of the luminescence decay curve.

Synthesis and electrical conductivity of crystalline and glassy alloys in the Ag3GeS3Br-GeS2 system by M. V. Moroz; P. Yu. Demchenko; O. G. Mykolaychuk; L. G. Akselrud; R. E. Gladyshevskii (867-871).
We have studied the formation of crystalline and glassy alloys in the Ag3GeS3Br-GeS2 system (0–52 mol % GeS2; Ag3GeS3Br is a glass-forming phase of variable composition) and determined the crystallographic parameters of the Ag3.179(9)Ge1.474(5)S4Br alloy as the saturated solid solution of GeS2 in Ag3GeS3Br: sp. gr. P213, a = 10.16572(3) Å, Z = 4. The electrical conductivity of the crystalline and glassy alloys was measured in the temperature range 250–410 K by a dc probe technique. The current carriers in the alloys are silver cations and halogen anions. We obtained materials with superionic conductivity and proposed a model for conduction in the alloys.

Magnetic phases in the Cu2GeSe3-Cr2Se3 system by T. G. Aminov; G. G. Shabunina; E. V. Busheva; V. M. Novotortsev (872-877).
We have studied the properties of magnetic phases in the Cu2GeSe3-Cr2Se3 system and identified a relation between the composition and magnetic structure of the phases, which can be divided into three groups according to their magnetic order. One group is an antiferromagnetic sample from the homogeneity range of the Cu2GeCr6Se12 compound (δ), containing 73 mol % Cr2Se3. Another group is constituted by spin glasses containing 65, 66.67, and 68.5 mol % Cr2Se3 in the homogeneity range of the Cu2GeCr4Se9 (γ) compound. The third group is a ferromagnetic sample in the same homogeneity range, containing 70 mol % Cr2Se3.

Information reliability evaluation of a Ge2Sb2Te5-based phase change memory cell by K. N. Egarmin; E. N. Voronkov; S. A. Kozyukhin (878-882).
The information reliability of phase change memory cells at different ambient temperatures has been assessed for the first time. The statistical approach chosen is based on A.N. Kolmogorov’s heuristic theory, which describes the kinetics of isothermal crystallization. We have analyzed the influence of the phase change memory cell size and critical size of crystalline nuclei, which depends on the physicochemical parameters of the material and temperature. The results demonstrate that the information reliability of phase change memory cells of typical dimensions can be sufficiently high up to 100°C. Calculation results are compared to available experimental data.

Effect of graphite nitrate exfoliation conditions on the released gas composition and properties of exfoliated graphite by M. I. Saidaminov; N. V. Maksimova; N. E. Sorokina; V. V. Avdeev (883-888).
We have studied the fundamental aspects of the exfoliation of intercalation compounds of natural flake graphite with nitric acid and proposed a technique for qualitative and quantitative in situ analysis of the gases forming during graphite nitrate exfoliation. We have examined the effects of the graphite nitrate exfoliation atmosphere, temperature, and time on the released gas composition and the properties of the resulting exfoliated graphite.

The effect of cobalt powder morphology on the microstructure of WC-Co hard alloys produced by sintering cobalt + tungsten carbide powder mixtures has been studied using X-ray diffraction, laser diffraction, scanning electron microscopy, density measurements, and Vickers microhardness tests. The results indicate that, under identical sintering conditions, the densest and most homogeneous microstructure is formed in hard alloys sintered using cobalt powders consisting of rounded particles. The use of cobalt powders with dendritic morphologies impedes the homogenization of Co + WC powder mixtures and preparation of pore-free WC-Co hard alloys.

Effect of the composition of mineral and organomineral mixtures on the tribological properties of friction pairs by L. B. Leont’ev; N. P. Shapkin; A. L. Leont’ev; A. L. Shkuratov; V. V. Vasil’eva (894-898).
We have studied the tribological properties of friction pairs of chromium-plated steel parts after processing with geomaterials: serpentinite, a natural silicate, a mixture of serpentinite and the silicate, a polysaccharide-modified natural silicate, and a mixture of serpentine and the polysaccharide-modified silicate. The abrasive used was quartz dust ranging in particle size from 1 to 5 μm, whose concentration reached 1%. The mixtures were shown to be highly effective in producing composite coatings on friction surfaces of parts. The incorporation of the polysaccharide-modified silicate into a friction joint considerably reduces its coefficient of friction and, as a consequence, the energy level of contact interaction.

We have studied the kinetics of corundum formation in supercritical water fluid from aluminum hydroxide (hydrargillite) and from the products of its thermal decomposition at 300°C over a period of 5 h. In all cases, the reaction involves the formation of boehmite, AlOOH, as an intermediate. The use of the product of the thermal decomposition of hydrargillite as a precursor considerably increases the reaction rate and reduces the induction period in comparison with the parent hydrargillite. Cobalt doping further increases the reaction rate and reduces the induction period. When the product of the thermal decomposition of hydrargillite is used as a precursor, the temperature dependence of the reaction rate constant shows Arrhenius behavior, whereas that for synthesis from uncalcined aluminum hydroxide has a more complex character.

The synthesis of silicon oxide and silicon nitride surface nanostructures is used as an example to demonstrate the possibility of using correlation relationships with inductive parametric constants for quantitatively assessing the reactivity of surface functional groups and predicting the conditions of surface reactions.

Structure and mechanical characteristics of ceramic Nb2O5 and Nb2(1 − y)Ta2y O5 by M. N. Palatnikov; O. B. Shcherbina; V. V. Efremov; A. A. Yanichev; N. V. Sidorov; V. V. Pasichnyi (909-915).
The structure and mechanical characteristics of ceramic Nb2O5 and ceramic materials produced from coprecipitated Nb2(1 − y)Ta2y O5 pentoxides by a conventional ceramic processing technique and exposure to high-intensity light have been studied by scanning probe microscopy and Raman spectroscopy.

Oxygen release from SrCo0.8Fe0.2O3 − δ by I. A. Starkov; S. F. Bychkov; A. A. Matvienko; A. P. Nemudry (916-922).
We have studied oxygen release from a membrane material with the composition SrCo0.8Fe0.2O3 − δ of various sizes in the temperature range 600–900°C in a flow reactor at oxygen partial pressures from 0.2 to 10−5 atm. The results demonstrate that the oxygen release from samples 50 μm to 2 mm in size at temperatures above 800°C can be described in terms of a quasi-equilibrium model. For fine powders, ≤63 μm in size, the temperature range of quasi-equilibrium oxygen release begins at t ≥ 600°C.

The incongruent melting of LiB3O5 (LBO) single crystals and transformations of the boron-oxygen groups in glasses and melts with the compositions Li2O · 2B2O3 and Li2O · 3B2O3 have been studied by Raman spectroscopy. The vapor over superheated melts of these condensed lithium borates has been shown to contain [BO2] radicals.

We have studied the formation of monovalent metal antimonate tungstates by solid-state reactions in the xM2CO3 · (yx)K2CO3 · ySb2O3 · 2(2 − y)WO3 (M = Na, Li; 0 ≤ xy; 1.0 ≤ y ≤ 2.0) systems and identified the stability regions of pyrochlore phases at a temperature of 1123 K in the KSbO3-WO3-MSbO3 (M = Na, Li) composition triangles. A model has been proposed for the ion distribution over the sites of the pyrochlore structure (sp. gr. Fd3m). The conductivity of the monovalent metal antimonate tungstates has been measured in the temperature range 500–1000 K, and a relationship between their ionic conductivity and structure has been established.

Sol-gel synthesis and properties of doped lanthanum chromite nanopowders by A. S. Anokhin; S. S. Strel’nikova; N. T. Andrianov; N. A. Makarov; D. A. Zhirov; K. A. Solntsev (935-938).
La1 − x Sr x CrO3 (0.2 ≤ x ≤ 0.3) powders have been prepared by a sol-gel process and dried in a microwave oven. Synthesis conditions were optimized using differential scanning calorimetry and mass spectrometry data. The phase composition of the synthesis products obtained at temperatures of 800, 850, 900, and 950°C was determined by X-ray diffraction. Scanning electron microscopy was used to determine the particle size of the powders and examine their morphology.

Mössbauer spectra and magnetic properties of Tm0.65Sr0.35Fe x Mn1 − x O3 (x = 0.3, 0.35, 0.4) by V. V. Parfenov; A. V. Pyataev; I. I. Nig’matullina; Sh. Z. Ibragimov (939-942).
We report Mössbauer spectroscopy results for Tm0.65Sr0.35Fe x Mn1 − x O3 (x = 0.3−0.4) at 300 and 80 K. Like in the case of lighter lanthanide ferromanganites, we observe phase separation of the magnetic sub- system: a magnetic phase shows up in the spectra in the form of a Zeeman sextet and “paramagnetic” dou- blets.

We demonstrate that the previously synthesized product of ethyl isothiocyanate insertion into tungsten hexachloride, WCl5{N(Et)C(S)N(Et)C(S)Cl}, whose partial hydrolysis yields {N(Et)C(S)-S-S-C=NH(Et)}[WOCl5] (I), can be used as a source of biologically active heterocyclic compounds. 1H and 13C NMR and gas chromatography-mass spectrometry data show that reaction of I with a saturated aqueous Na2CO3 solution yields a number of thiazolidine heterocycles, mostly 4-ethyl-5-ethylimino-[1,2,4]-dithiazolidin-3-trithione. The thermal Dimroth rearrangement leads to the formation of 2,4-diethyl-[1,2,4]-dithiazolidin-3,5-dithione and the products of partial hydrolysis of both heterocycles: 4-ethyl-5-ethylimino-[1,2,4]-dithiazolidin-3-on and 2,4-diethyl-3-thioxo-[1,2,4]-dithiazolidin-5-on.

Preparation of ZrF4-NaF-BaF2-LaF3-YbF2 glasses with YbF2 substitution for BaF2 (LaF3) by A. P. Ivanenko; N. M. Kompanichenko; A. A. Omel’chuk; R. N. Savchuk; V. F. Zinchenko (947-952).
We have prepared glasses and semicrystalline phases with a green color in the systems ZrF4(53.5)-NaF(20)-BaF2(20)-LaF3(6.5 − x)-YbF2(x) (0 ≤ x ≤ 6.5 mol %) (I) and ZrF4(53.5)-NaF(20)-BaF2(20 − x)-LaF3(6.5)-YbF2(x) (0 ≤ x ≤ 20 mol %) (II). Thermal analysis results demonstrate that, in both systems, the glass transition temperature of the samples containing ≤3 mol % YbF2 lies in the range 200–250°C, their heating curves show two or three crystallization events (at 320–340, 380–460, and 415–490°C), and their melting points range from 460 to 490°C. Increasing the YbF2 content of the glasses to 4 mol % and above (system I) has no effect on their glass transition temperature, reduces the temperature of the first crystallization event from 340 to 305°C, and produces extra peaks in the range 545–600°C, above the major melting peak, which can be accounted for by a nonequilibrium state of the glasses. Ytterbium difluoride substitution for barium difluoride (10 to 20 mol %) (system II) leads to the formation of semicrystalline phases and increases the glass-transition (305°C), crystallization (470–515°C), and melting (570–690°C) temperatures. The IR spectra of such samples show, in addition to a so-called “featureless continuum” (∼500 cm−1), absorption bands characteristic of the Yb-F bond. Electronic spectra also confirm that the glasses contain both divalent and trivalent ytterbium.

Formation and crystallization of chlorine- and bromine-containing hafnium fluoride-based glasses by M. N. Brekhovskikh; L. N. Dmitruk; L. V. Moiseeva; V. A. Fedorov (953-956).
We have studied glass-forming regions for ZBLAN-type hafnium fluoride-based glasses with the compositions (63–53)HfF4 · 20BaF2 · 4LaF3 · (1–3)InF3 · (0–20)NaF in which fluorine anions are partially replaced by chlorine and bromine anions. The crystallization mechanism of the glasses has been investigated by differential thermal analysis and X-ray diffraction. The results demonstrate that characteristic features of the glasses are a significant decrease in glass transition temperature (t g) and the precipitation of fine-particle crystalline chloride and bromide phases at temperatures well below the crystallization temperature (t x) of their fluoride analogs. We have studied the effect of the Cl/F and Cl/Br ratios in the glass batch and the melt cooling rate after glass preparation on the crystallization behavior of the glasses and determined the heat treatment temperature and time for the formation of transparent glass-ceramic samples upon heat treatment in the temperature range where chloride and bromide phases precipitate. Doping of the glasses with 1 at % or smaller amounts of rare-earth metals is found to have no significant effect on the phase segregation process during heat treatment.

Effect of barium on the structure and dielectric properties of multicomponent ceramics based on ferroelectric relaxors by M. V. Talanov; O. N. Razumovskaya; L. A. Shilkina; L. A. Reznichenko (957-961).
High-density ceramic samples of mPb(Mg1/3Nb2/3) · yPb(Zn1/3Nb2/3) · nPb(Ni1/3Nb2/3) · xPbTiO3 (m = 0.4541, y = 0.0982, n = 0.1477, x = 0.3) solid solutions, unmodified and barium-modified, with the composition lying in a morphotropic phase region, have been prepared by a conventional ceramic processing technique. We demonstrate that barium substitution for 5% of the lead on the A site allows one to obtain ceramics containing no pyrochlore phase. Modification with barium shifts the solid solution from the morphotropic to a tetragonal phase region. In addition, barium doping increases the average grain size of the ceramic from 2–3 to 3–4 μm and changes the type of fracture from intergranular to mixed (intergranular and transgranular). Modification with barium increases the relative dielectric permittivity ɛ/ɛ0 (at E = 0) of the material by more than a factor of 2 (from 4300 to 9100). We conclude that materials based on the ceramics studied can find practical application and examine ways of further improving their piezoelectric performance.