Pressure dependences of the elastic constants of PbTe, SnTe and Ge0.08Sn0.92Te

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 Ge 0.08 Sn 0.92 Te 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 C 111 ; 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 Ge 0.09 Sn 0.92 Te; the large anisotropy found has been explained in terms of the strong influence of the nearest-neighbour repulsive forces on C 111 . The elastic stiffness constants of SnTe have been measured as a function of pressure up to 15*10 8 Pa, quite close to the phase transition pressure of 18*10 8 Pa. C 44 softens somewhat over about 9*10 8 Pa.