Inorganic Materials (v.49, #8)

Structure and surface morphology of Si1 — x Ge x layers grown on Si/sapphire by molecular beam epitaxy using a sublimation silicon source and gaseous germanium source by S. A. Matveev; S. A. Denisov; V. Yu. Chalkov; V. G. Shengurov; D. E. Nikolichev; A. V. Boryakov; V. N. Trushin; E. A. Pitirimova (749-753).
Si1 − x Ge x epilayers have been grown on silicon-on-sapphire structures by molecular beam epitaxy using a sublimation silicon source and gaseous germanium source. Si1 − x Ge x layers grown directly on sapphire substrates had poorer structural perfection, so Si buffer layers were used in subsequent growth runs. Using X-ray photoelectron spectroscopy, we determined the concentration-depth profiles of Si, Ge, and background impurities across the layers. Varying the Si buffer thickness in the range 50–300 nm was shown to have no effect on the structure of the SiGe layers. Single-crystal SiGe layers were obtained at substrate temperatures in the range 360–410°C. Varying the germanium concentration in the range 5–25% had no effect on the structure of the layers but slightly increased their roughness.

We have studied the effect of continuous band-gap photoexcitation intensity on the extrinsic photosensitivity of structures based on semi-insulating GaAs with an epitaxial GaAs〈S〉 layer (n = 7 × 1015 cm−3). The results demonstrate that combined photoexcitation leads to sensitization of the structure in the low-energy (hν < 0.76 eV) region of the impurity photoconductivity spectrum owing to arsenic vacancies, isolated or involved in the formation of donor-acceptor pairs, which act as donors. The observed increase in photosensitivity in the spectral range hν < 0.76 eV is due to the increase in the concentration of (D 0-A 0)0* excited pairs. Weakly photoactive trapping centers (which are commonly studied by thermally stimulated conductivity measurements) can be identified by analyzing the temperature dependence of impurity photoconductivity due to deep centers at E c − (0.95–1.15) eV.

Using X-ray diffraction and scanning electron microscopy, we have studied general aspects of defect structure formation in thermoelectric materials in different stages of plastic flow in the equal-channel angular pressing process with three channels. The results demonstrate that materials prepared using this deformation configuration have a fine-grained, homogeneous microstructure with a favorable texture, such that the cleavage planes of the grains are oriented along the extrusion axis. Studies of the structure and properties of the thermoelectric materials allowed us to optimize the equal-channel angular pressing temperature, which should be below the recrystallization onset temperature.

Heat capacity of ZnTe above 298 K by A. S. Pashinkin; M. S. Mikhailova; V. A. Fedorov (763-765).
We have studied the temperature dependence of heat capacity for ZnTe at temperatures above 250 K. Based on analysis of the present and previous heat capacity data, we recommended the most reliable data in the temperature range 250–1000 K.

Some aspects of the chemical bonding in antimony by A. A. Ashcheulov; O. N. Manyk; T. O. Manyk; S. F. Marenkin; V. R. Bilynskiy-Slotylo (766-769).
We have studied the key features of the chemical bonding in hexagonal and rhombohedral antimony and determined polymorphism boundaries that would allow one to extend technological potentialities of creating novel antimony-based materials.

Hydride phases based on the intermetallic compounds LaNi5, CeCo3, NdNi3, GdFe3, DyCo3, and ErNi3 have been synthesized at a hydrogen pressure of 10 MPa and a temperature of 273 K. The phase composition of the synthesized materials and the lattice parameters of the hydride phases have been determined by X-ray diffraction. During storage in air at room temperature, the hydrides decompose more slowly than do their analogs synthesized at low pressure. The hydrogen content of the hydrides is higher than or similar to that of hydride phases synthesized at high pressure. X-ray diffraction results for the low-temperature RT3-based intermetallic hydrides demonstrate that their lattice is expanded to a lesser extent than that of their high-pressure analogs.

Formation of small volatile complexes during copper film growth by the combined synthesis-transport method by A. M. Badalyan; M. S. Polyakov; V. V. Kaichev; V. A. Nadolinnyi; I. K. Igumenov (775-780).
Stable heterogeneous synthesis products in combined synthesis-transport processes for the growth of thin copper films have been studied by ESR, X-ray photoelectron, and IR spectroscopies. The results demonstrate that the synthesized volatile compounds condensed on solid surfaces have the form of formate-like metal complexes of copper(I). We have identified the mechanisms underlying the formation of volatile monomeric metal complexes on the surface of copper-containing precursor particles and the mechanism of the thermal decomposition of metal complexes on a heated substrate.

High-temperature synthesis of cast Cr2AlC at an inert gas overpressure by P. A. Miloserdov; V. A. Gorshkov; V. I. Yukhvid (781-785).
This paper reports the high-temperature synthesis of cast Cr2AlC from mixtures of chromium(III) oxide, chromium(VI) oxide, aluminum, and carbon at an increased inert gas (Ar or N) pressure in a 3-L self-propagating high-temperature synthesis reactor at an initial argon pressure p i = 5 MPa. The reaction products were characterized by X-ray diffraction and X-ray microanalysis. The results indicate that the ingots obtained under optimized conditions consisted of Cr2AlC and Cr3C2 with a ratio of about 85 : 15.

Preparation and characterization of mesoporous TiO2-Al2O3 composites by T. A. Sedneva; E. P. Lokshin; M. L. Belikov; A. I. Knyazeva (786-794).
We have established conditions for the synthesis of multiphase nanocomposites in a wide range of TiO2/Al2O3 ratios. The nanocomposites have a thermally stable mesoporous structure and large specific surface area. Some of them exhibit photocatalytic activity at λ ≥ 670 nm.

We have studied the distinctive features of the reaction between titania and molybdenum trioxide in the sol-gel synthesis of TiO2/MoO3 composite materials (1–10 mol % MoO3). The results demonstrate that interactions between phases, which depend on MoO3 concentration in the composites and are stronger at higher heat-treatment temperatures, lead to suppression of titania crystallization, inhibit the anatase-to-rutile phase transition, and influence the morphology and structural perfection of the oxide phase.

Growth and optical properties of synthetic opal filled with Bi12SiO20 and Bi12GeO20 nanocrystals by V. S. Gorelik; G. I. Dovbeshko; A. V. Evchik; V. N. Moiseenko; M. P. Dergachev (802-806).
We report a technique for producing Bi12SiO20 and Bi12GeO20 nanocrystals in pores of synthetic opal. Bragg reflection and Raman spectroscopies are used to assess the degree of filling of opal pores and diagnose the state of the substance in the pores. The substance in the pores is shown to be in a crystalline state. The measured Raman spectra of the nanocrystals are compared to those of powders and single crystals. The spectra of the photonic crystals obtained contain new lines. We observe intensity redistribution at low frequencies and changes in the frequency of several Raman lines compared to the spectra of powders and single crystals.

Ca10.5 − x Pb x (PO4)7 and Ca9.5 − x Pb x M(PO4)7 ferroelectrics with the whitlockite structure by D. V. Deyneko; S. Yu. Stefanovich; A. V. Mosunov; O. V. Baryshnikova; B. I. Lazoryak (807-812).
We have prepared Ca9.5 − x Pb x M(PO4)7 (M = Mg, Zn, Cd) and Ca10.5 − x Pb x (PO4)7 solid solutions. A polar whitlockite-like (sp. gr. R3c) crystal structure exists in the range 0 ≤ x ≤ 1.5 for all of the M cations in Ca9.5 − x Pb x M(PO4)7 and in the range 0 ≤ x ≤ 2.5 for Ca10.5 − x Pb x (PO4)7. X-ray powder diffraction profile analysis results for Ca8.5PbCd(PO4)7 powder demonstrate that the small divalent M cations reside predominantly on the octahedral site M5 of the whitlockite structure, the calcium cation occupy the M1–M3 sites, and the lead cations are located primarily on the M4 site. Differential scanning calorimetry, second-harmonic generation, and dielectric permittivity data indicate that all of the synthesized phosphates are high-temperature ferroelectrics. The highest Curie temperatures are offered by the x = 0.5 materials, in which most of the lead resides in the spacious oxygen polyhedra M4 and only a small amount of lead is incorporated into the smaller polyhedra around M1–M3. The nonlinear optical activity has a maximum in the middle of the solid-solution series and is an order of magnitude higher than that of the parent, lead-free phases.

Synthesis of nanostructured sodium calcium tripolyphosphate using organic templates by L. S. Skogareva; V. K. Ivanov; O. S. Ivanova; A. E. Baranchikov; T. A. Tripol’skaya; Yu. D. Tret’yakov (813-820).
We have developed a process for the synthesis of nanostructured sodium calcium tripolyphosphate with the use of organic templates, including amino acids (glycine and L-aspartic, L-glutamic, and ɛ-aminocaproic acids), polysaccharides (sodium and calcium alginates and maltodextrin), and Trilon B. The synthesized sodium calcium tripolyphosphate nanopowders have been characterized by scanning electron microscopy, X-ray diffraction, and IR spectroscopy. The particle size of the nanopowders is shown to be determined by the properties of the template and ranges from ∼20 nm to ∼20 μm. We have studied the biological activity of peroxo derivatives of sodium calcium tripolyphosphate for Escherichia coli.

Radiation hardness of lithium niobate nonlinear optical crystals doped with Y, Gd, and Mg by M. N. Palatnikov; I. N. Efremov; N. V. Sidorov; O. V. Makarova; V. T. Kalinnikov (821-825).
We have studied the effect of gamma irradiation to various doses on optical characteristics (optical transmission spectra) of nominally undoped, rare earth-doped, and alkaline earth-doped lithium niobate crystals: LiNbO3, LiNbO3:Y (0.46 wt %), LiNbO3:Y,Mg (0.32, 0.24 wt %), LiNbO3:Mg (0.27 wt %), and LiNbO3:Gd (0.004, 0.04, 0.26, 0.43 wt %). We have examined the influence of the ionizing radiation dose, the nature of dopants, and their concentration on the optical transmission of the gamma-irradiated doped lithium niobate crystals. The results suggest that gamma-induced changes in the optical transmission of LiNbO3:Gd (≃0.004 and 0.04 wt %) crystals can be used for gamma dosimetry in the dose range ≃101 to 1.5 × 104 rad.

Preparation and dielectric properties of potassium sodium niobate-based solid solutions by G. M. Kaleva; A. V. Mosunov; S. Yu. Stefanovich; E. D. Politova (826-833).
We have prepared ceramic samples of solid solutions based on Bi-containing perovskite-like oxides near the morphotropic phase boundary in the K0.5Na0.5NbO3-BiScO3-AgSbO3 system and modified with LiF and MnO2 additions; investigated the phase relations, structure, and dielectric and ferroelectric properties of the ceramics; and determined their phase transition temperatures. The choice of superstoichiometric additives capable of intensifying the sintering process has been substantiated, and the effect of the additives on the Curie temperature of the ceramics has been examined.

Thermal and luminescent properties of M2Zn(VO3)4 (M = Rb, Cs) by B. V. Slobodin; A. V. Ishchenko; R. F. Samigullina; B. V. Shul’gin (834-838).
We have developed processes for the synthesis of the Rb2Zn(VO3)4 and Cs2Zn(VO3)4 tetrametavanadates. Rb2Zn(VO3)4 has been prepared by solid-state reaction (350°C) between presynthesized RbVO3 and ZnV2O6 powders, and Cs2Zn(VO3)4 has been prepared by the Pechini method (sol-gel process). Both metavanadates crystallize in monoclinic symmetry (sp. gr. P21/m). Thermochemical characterization results demonstrate that the vanadates undergo complex transformations during heating to 450°C and subsequent cooling. As a result, the materials are in a nonequilibrium state at room temperature and consist of both the parent double metavanadates and their peritectic decomposition products. We believe that the formation of the structure of the M2Zn(VO3)4 compounds from their melts is a kinetically hindered process. These compounds are structurally stable only at temperatures below 369 (Rb2Zn(VO3)4) or 420°C (Cs2Zn(VO3)4). We have measured for the first time the diffuse reflectance and photoluminescence excitation spectra of the two tetrametavanadates in their emission range and their photoluminescence spectra at various excitation wavelengths and determined their chromaticity coordinates. Their X-ray luminescence and scintillation decay characteristics have been determined for the first time under pulsed electron beam excitation. The electron excitation dissipation processes in the cesium and rubidium compounds are shown to be similar. We discuss the origin of the emission bands in the mixed vanadates and their potential application areas.

We have developed a new method for determining oxygen nonstoichiometry (3 − δ) as a continuous function of oxygen partial pressure $$left( {p_{O_2 } } ight)$$ at high temperatures in mixed ionic-electronic conducting oxides. A proposed mathematical model allowed us to assess the contribution of the oxygen released from a sample to the oxygen partial pressure at the outlet of a flow reactor after a steplike change of oxygen partial pressure in the incoming gas from 0.2 to 10−5 atm and to calculate 3 − δ as a function of $$p_{O_2 }$$ . The accuracy of the method was demonstrated by comparing our experimental data and data in the literature for the well-studied oxygen-ion-conducting membrane materials SrCo0.8Fe0.2O3 − δ and Ba0.5Sr0.5Co0.8Fe0.2O3 − δ

X-ray diffraction study of the NaF-LiF-NdF3 eutectic in the liquid and solid states by V. E. Sokol’skii; A. S. Roik; A. O. Davidenko; N. V. Faidyuk; R. N. Savchuk (844-851).
The ternary eutectic alloy with the composition 33 mol % NaF + 53 mol % LiF + 14 mol % NdF3 has been studied in the liquid and crystalline states using differential thermal analysis and X-ray diffraction at room and high temperatures. The results demonstrate that the alloy undergoes no phase transformations below its melting point: the only phases identified with certainty are NaF, LiF, and NaNdF4. The melt contains complex microgroups differing in cation composition. Analysis of structural models for the melt indicates that there is no dense noncrystalline packing of the fluorine anions, in contrast to what was observed previously in the eutectic NaF-LiF-LaF3 melt.

Thermodynamic properties of the Al-Eu-Sn melts by M. I. Ivanov; V. V. Berezutski; V. G. Kudin; M. A. Shevchenko; V. S. Sudavtsova (852-855).
Mixing enthalpies of melts of the binary systems Al-Eu at 1300–1473 K (in the concentration ranges 0 < x Eu < 0.2 and 0.57 < x Eu < 1) and Eu-Sn at 1250–1300 K (0 < x Sn < 0.2; 0.51 < x Sn < 1) were studied for the first time by the isoperibolic calorimetry technique. It was determined that there are moderate (ΔHmin = −23 kJ/mol at x Eu = 0.39) and large (ΔHmin = − 63 kJ/mol at x Sn = 0.42) exothermic formation effects for these melts, correspondingly. Using the information obtained by us and taken from literature, thermodynamic properties of these melts were calculated in the wide temperature range by the model of ideal associated solutions (IAS). The mixing enthalpies of melts of the ternary Al-Eu-Sn system were modeled using the analogous data for the binary boundary systems.