Pressure dependences of the elastic constants of PbTe, SnTe and Ge_0.08Sn_0.92Te

Abstract

Measurements of the effects of hydrostatic and uniaxial pressures on ultrasonic wave velocities have been used to determine the six third-order elastic constants of PbTe. The hydrostatic pressure dependences of the elastic stiffness constants of SnTe and Ge0.08Sn0.92Te have also been obtained. Estimation of the third-order constants of PbTe on the basis of a Born-Mayer potential has established that nearest-neighbour repulsive forces are predominantly responsible for the large negative value of C111; however, this ionic model does not generally account well for the observed third-order elasticity of this mixed ionic-covalent compound. The Gruneisen mode gammas in the long-wavelength limit have been calculated for PbTe, SnTe and Ge0.09Sn0.92Te; the large anisotropy found has been explained in terms of the strong influence of the nearest-neighbour repulsive forces on C111. The elastic stiffness constants of SnTe have been measured as a function of pressure up to 15*108 Pa, quite close to the phase transition pressure of 18*108 Pa. C44 softens somewhat over about 9*108 Pa.