Vol 52, No 6 (2016)

We derive analytical expressions for the free energy of mixing of (YbTe)_х(PbTe)_1–х and (YbTe)_х(SnTe)_1–х solid solutions in the temperature range 600–1095 K and accurately determine the location of their phase boundaries. Т–х–у relations for the solidus surface and the spinodal decomposition of solid solutions in the pseudoternary system YbTe–PbTe–SnTe are found.

The characteristic details of the carbothermal synthesis of TiB₂ powders from the stoichiometric mixture TiO₂–H₃BO₃–C at temperatures lower 1700 K are investigated using thermal analysis (ТG—thermogravimetry and DSC—differential scanning calorimetry), as well as X-ray diffraction and scanning electron microscopy. In the temperature interval 300 K → 1673 K → 1273 K and at a heating rate of 10 K/min, the reaction in the powder mixture begins at approximately 1300 K and ends at 1470 K during cooling. After 3 h of isothermal synthesis at 1473 K, the TiB₂ yield is more than 90%. The resulting products are hexagonal plate-like crystals 5–10 μm across with thickness of 3 to 4 μm. Kinetic analysis showed that in the temperature range of 1330 to 1673 K the TiB₂ synthesis reaction is of the first-order, and the calculated activation energy of the process is 315 ± 24 kJ/mol.

We have identified structural and morphological changes produced by irradiation with 167-MeV ⁺²⁴Xe¹³⁶ ions to a fluence of 5.3 × 10¹⁴ cm^–2 in Ti, Zr, and Hf nitrides prepared using oxidation-assisted engineering. Irradiation of TiN_x and HfN_x leads to the formation of nano- and micropores in the surface layer of the samples. The surface layer of ZrN_x samples contains nanopores both before and after irradiation. The presence of pores in the unirradiated ZrN_x samples probably ensures the possibility of structural relaxation without further pore formation under irradiation. The irradiated ZrN_x samples have local crystal structure distortions unrelated to dislocations and attributable to the impact of high-energy xenon ions.

The heat capacity of InVO₄ has been determined by differential scanning calorimetry in the temperature range 339–1089 K. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of indium orthovanadate: enthalpy increment H°(T)–H°(339 K), entropy change S°(T)–S°(339 K), and reduced Gibbs energy Ф°(Т). The specific heats of GaVO₄ and TlVO₄ have been evaluated.

Gd₂Sn₂O₇ gadolinium stannate with the pyrochlore structure has been prepared by solid-state reaction and its high-temperature heat capacity has been determined by differential scanning calorimetry in the temperature range 350–1020 K. The C_p(T) data are shown to be well represented by the classic Maier–Kelley equation. The experimental C_p(T) data have been used to evaluate the thermodynamic functions of gadolinium stannate: enthalpy increment H°(T)–H°(339 K), entropy change S°(T)–S°(339 K), and reduced Gibbs energy Ф°(Т).

We have studied the thermal, electrical, and thermoelectric properties of Ca_3–xBi_xCo₄O_{9 + δ} (0.0 ≤ x ≤ 1.5) ceramics prepared by solid-state reactions. Phase-pure Ca_3–xBi_xCo₄O_{9 + δ} solid solutions were obtained at x ≤ 0.3. The samples with 0.3 < x < 1.5 consisted of three phases: Ca_2.7Bi_0.3Co₄O_{9 + δ}, Bi₂Ca₂Co_1.7O_y, and Со₃О₄. The sample with the composition Ca_1.5Bi_1.5Co₄O_{9 + δ} consisted of two phases: Bi₂Ca₂Co_1.7O_y and Co₃O₄. The materials are p-type semiconductors with linear thermal expansion coefficients in the range (10.6–12.8) × 10^–6 К^–1. Their electrical and thermal conductivities are nonmonotonic functions of x, and their thermoelectric power increases with increasing x. The mixed-phase ceramics have been shown to have better thermoelectric properties: the highest thermoelectric power factor, ≈0.24 mW/(m K²) at T = 1100 K, is offered by the ceramics with x = 0.9–1.0, which contain nearly equimolar amounts of Ca_2.7Bi_0.3Co₄O_{9 + δ} and Bi₂Ca₂Co_1.7O_y. This power factor is 2.5 times that of the layered calcium cobaltite Ca₃Co₄O_{9 + δ} and solid solutions based on it: 0.094–0.098 mW/(m K²) at the same temperature.

Differential scanning calorimetry (DSC) characterization of tellurite glasses doped with lanthanum oxide, which improves their crystallization resistance, has revealed a phase transformation specific to such glasses, in which partial crystallization of a sample is followed by melting of the crystals formed. The experimentally observed dependence of the decrease of crystallization–melting peaks across a series of disperse samples of (TeO₂)_0.72(WO₃)_0.24(La₂O₃)_0.04 glass with increasing particle size upon extrapolation to the size of a bulk sample has been used to assess the crystallization resistance of tellurite glasses for optical applications. The assessment technique comprises DSC characterization of particle-size-classified glass samples and the use of a mathematical model for obtaining the degree of crystallization as a function of temperature and time, α(T, t) through analysis of nonisothermal DSC peaks representing a partial glass crystallization process passing into melting. The crystallization resistance of glass is estimated by extrapolating the maximum α values as a function of particle size to a preform size. Tested for (TeO₂)_0.72(WO₃)_0.24(La₂O₃)_0.04 glass, the technique offers the possibility of selecting preforms for producing fibers from compositionally new, chemically pure tellurite glasses at a given phase purity level.

We present results of experimental studies of structure formation in SHS materials under conditions combining combustion and high-temperature deformation. Such conditions are realized by the unconstrained SHS compression method proposed here, which allows the moldability of a material being synthesized to be assessed under real technological conditions. We discuss the capability of combustion products for high-temperature plastic deformation in the case of various SHS materials in relation to the ratio of the combustion temperature to the melting points of the starting components and combustion products during synthesis.

The simplest components (atoms, diatomic molecules, and simple free radicals) of an inductively coupled rf plasma in a hexamethyldisilazane–argon mixture have been identified by optical emission spectroscopy. We have studied the influence of process conditions (plasma power and hexamethyldisilazane concentration in the mixture) on the intensity of lines and bands corresponding to these components and the corresponding changes in the composition and physicochemical properties of SiC_xN_yH_z films grown in this plasma.