Vol 55, No 10 (2019)

We have studied the influence of a preload applied to a starting elemental powder mixture and the strain in the product of high-temperature synthesis during a bulk exothermic reaction on the grain structure of the Ni₃Al intermetallic compound and the temperature dependence of its strength. The results demonstrate that, during the bulk exothermic reaction responsible for the formation of the intermetallic compound under pressure in a closed press die, the average grain size varies along a vertical cut, from the minimum value on the upper and lower surfaces of the synthesized sample to the maximum value in its central part. As the preload applied to the starting powder mixture is raised, the average grain size decreases, whereas the general character of the grain size distribution in a cross section of the sample remains unchanged. Deformation of the high-temperature synthesis product in a press die with partial extrusion causes an appreciable grain size reduction, significantly averaging the grain size in the bulk of the synthesized sample, and raises the tensile strength of the intermetallic compound in the temperature range 20–1000°C.

Complex oxides in the Sm₂O₃–CaO–MO and Ln₂O₃–SrO–MO systems (Ln = Sm, Gd; M = Fe, Co) were prepared via the glycerol-nitrate technique at 1100°С in air. The homogeneity ranges for the solid solutions were determined as follows: Sr_1 – хGd_хCoO_{3 – δ} (0.1 ≤ х ≤ 0.4); Sr_2 – yGd_yCoO_4 – δ (0.8 ≤ y ≤ 1.2); Sr_1 – хGd_хFeO_3 – δ (0.05 ≤ х ≤ 0.30 and 0.80 ≤ х ≤ 1.0); Ca_1 – xSm_xFeO_3 – δ (0.70 ≤ x ≤ 1.0); Sr_2 – ySm_yFeO_4 – δ (0.7 ≤ y ≤ 0.8); Sr_2 – yGd_yFeO_4 – δ (0.75 ≤ y ≤ 0.8); Ca_2 – уSm_уFeO_4 – δ (у = 0.90); Sr_3 – zSm_zFe₂O_7 – δ (0 ≤ z ≤ 0.3 and z = 1.8); and Sr_3 – zGd_zFe₂O_{7 – δ} (0 ≤ z ≤ 0.3 and z = 1.9). For all single phase oxides, the crystal structure was determined and the unit cell parameters, the unit cell volume, and the structural parameters were refined.

The electrical conductivity (σ) and thermoelectric power (S) of Ca_{1 –x}Bi_xMnO_{3 – δ} (х = 0.05, 0.10, 0.15) manganites with a perovskite-like structure have been measured in air in the temperature range 298–1223 K. Doping with bismuth increases the electron charge carrier concentration and leads to an increase in σ and S. The observed decrease in σ and S with increasing temperature is due to partial Mn³⁺ disproportionation into Mn²⁺ and Mn⁴⁺.

This paper presents a study of the structure of the Nd_0.85Ba_0.15MnO₃ compound and its stability at a reduced oxygen partial pressure. Structural characteristics of Nd_0.85Ba_0.15MnO₃ have been determined by X-ray diffraction. The sequence of phase transformations in the Nd–Ba–Mn–O system as the oxygen pressure decreases from atmospheric to –21 atm has been identified by a static method using a vacuum circulation apparatus.

The crystallization kinetics of extrapure bismuth-doped Ge–S glasses, GeS_x〈nBi〉 (1.25 ≤ х ≤ 1.6, n = 1 at %), have been studied by differential scanning calorimetry (DSC) in the range 320–1000 K. A technique proposed for analysis of crystallization peaks offers the possibility of describing them with an accuracy comparable to that of the Erofeev semiempirical model and includes analytical expressions for the degree of crystallization, α(t,Т), further developing a simplified version of the Kolmogorov–Johnson–Mehl theory. The kinetic characteristics of glass crystallization in α(t,Т) found using this technique and graphical representation of the data in the form of a time–temperature–transition (TTT) diagram make it possible to optimize the optical fiber drawing temperature and time.