Elastic Characteristics of Laminated Gallium and Indium Chalcogenides

Abstract

Laminated gallium and indium chalcogenides are promising materials for the construction of mechanoelectrooptical sensors operating at high temperatures and pressures in aggressive media. The high-temperature annealing of these crystals in different atmospheres distorts their lattice, induces thermal stresses, and affects the elastic characteristics [1–5]. In what follows, we establish the exact values of the lattice constants of gallium and indium monochalcogenides in a broad temperature range and analyze the behavior of their elastic characteristics depending on the chemical composition and temperature. The Ga Te, Gax Se1 – x , Ga S, Inx Se1 – x , and Gax In1 – x Se alloys are synthesized by fusion in evacuated ampoules according to the procedure proposed in [6]. In the as-synthesized state, they have a well-pronounced laminated structure. The influence of temperature on the lattice constants of the crystals was studied with the help of a DRON-3 diffractometer in the monochromatic Cu Kα-radiation by scanning with steps of 0.05°. In this case, either an UVD-2000 (VR-5/20) high-temperature attachment [under the conditions of rarefied atmosphere (up to 13 mPa)] and an URNT-180 low-temperature attachment were used or the specimens were tested under the conditions of free inflow of air (the specimens were cooled by a flow of vapor of liquid nitrogen with automatic maintenance of temperature within the range ± 0.3 K) according to the well-known procedures [7, 8]. In the course of the tests, the temperature varied within the range ± 3 K. Oil-free zeolite getter-ion pumps mounted in the case where used to ensure the possibility of free rotation of the chamber on the goniometer. The minimum absorption of X-rays was attained by using beryllium sheets pasted to the case with a K-400 high-temperature glue stable in vacuum. The thickness of a window in the zone of penetration of X-rays was not larger than 0.5 mm. The accuracy of evaluation of the lattice constants was ± 0.001 A. The experimental data confirm the linear dependence of the lattice parameters of gallium and indium monoselenides on temperature (see Fig. 1). No abrupt changes (corresponding to phase transitions) were recorded. For In Se, the coefficient of linear thermal expansion along the a-axis remains constant at low temperatures and close to 10.5 ⋅ 10– 6 ; along the c-axis, this coefficient is equal to 2.3 ⋅ 10– 6 in agreement with the wellknown literature data [9, 10]. A similar tendency is observed for the Ga Se compound. In this case, the coefficient of linear thermal expansion is equal to 5.5 ⋅ 10– 6 along the a-axis and 1.15 ⋅ 10– 6 along the c-axis. Note that, at low temperatures, the physicochemical properties of high-resistance laminated crystals depend on large-scale inhomogeneities responsible for the formation of a nonuniform potential pattern. In this case, the mobility of charge carriers in the direction perpendicular to the layers is determined by the height of the drift barriers [11, 12]. According to the data of X-ray diffraction analysis, the X-ray diffraction patterns of the freshly prepared Ga0.47 Se0.53 alloy are indexed in the rhombohedral lattice of the γ-3R modification of Ga Se. Moreover, the 00l lines are thin and the other lines are blurred and thick. The analysis of the intensity of the (1010) line (one of the most typical in the γ-3R modification) by the method of high-temperature radiography shows that it is stable up to temperatures close to the melting point, despite the increase in the energy of thermal oscillations of atoms in the lattice.