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

Abstract

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 σ_c is 55 ± 12 MPa. With increasing temperature, σ_c varies only slightly, but at 620 K the samples become more plastic and their relative elongation ε_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.