Elastic wave propagation in Bi1⋅60Sb0⋅40Te3 and Bi2Te3

Abstract

The six independent elastic constants of the monocrystalline, pseudo-binary alloy Bi1·60Sb0·40Te3 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 Bi1.60Sb0.40Te3 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.