Crystallization and mechanical properties of solid solutions between bismuth and antimony chalcogenides

Using scanning electron microscopy, we have studied how the conditions of preparation of granules of Sb2Te3-Bi2Te3 and Bi2Te3-Bi2Se3 solid solutions through melt solidification in a liquid influence their morphology, fractographs of fracture surfaces of samples prepared by hot-pressing the granules, and the contents of the major components in the samples. The granules are rounded (solidification in water and liquid nitrogen) or platelike (solidification in water under an excess pressure and in liquid-nitrogen-cooled ethanol) in shape. Fracture surfaces of hot-pressed samples prepared from granules comminuted in a ball mill have a uniform, fine microstructure, with faceted grains several microns in size. Characteristically, samples prepared from granules comminuted in a cutting mill have transgranular layered fractures, with layers up to hundreds of microns in thickness. The mechanical properties of the samples (ultimate strength and relative elongation) have been studied using compression tests at temperatures of 300 and 620 K. The samples experience brittle fracture. Their compression strength sigma(c) is 55 +/- 12 MPa. With increasing temperature, sigma(c) varies only slightly, but at 620 K the samples become more plastic and their relative elongation epsilon(b) increases by a factor of 2-4. The ultimate strength of hot-pressed samples prepared by uniaxial compression is 20% higher than that of samples prepared by biaxial compression.