Elastic wave propagation in Bi_1⋅60Sb_0⋅40Te₃ and Bi₂Te₃

Abstract

The six independent elastic constants of the monocrystalline, pseudo-binary alloy Bi_1·60Sb_0·40Te₃ have been measured by the ultrasonic pulse-echo technique. The elastic behaviour is compared and contrasted with those of Bi₂Te₃ and the group V semimetals with crystal structures belonging to the same point group, ¯3m. Elastic wave-velocity surface cross-sections, particle displacement and energy flux vectors are presented and discussed; the pure mode axes — knowledge of which is most useful in experimental ultrasonic studies — are given. Elastic wave propagation in Bi_1.60Sb_0.40Te₃ and Bi₂Te₃ shows characteristics expected for layer-type crystals with weak interlayer binding, i.e., comparatively large ultrasonic velocities in thexy plane and lower velocities along the direction (z) of weakest binding.