Higher order elasticity of amorphous As₂S₃

Abstract

Abstract The third-order elastic constants of amorphous As2S3 have been determined from measurements of the effects of hydrostatic and uniaxial pressure on ultrasonic wave velocities. They are found to be negative, in contrast to those of silica-based glasses, which are anomalously positive. The third-order elastic constant results, combined with the temperature dependences and the second pressure derivatives of the second-order elastic constants, have been used to estimate the fourth-order elastic constants. These complete sets of third- and fourth-order constants provide the coefficients of the Hamiltonian with respect to strain, and hence knowledge of the anharmonicity of the long-wavelength vibrational states of a chalcogenide glass. Positive Grüneisen parameters obtained for both longitudinal (γ1 = +2·6) and transverse (γt = + 2·4) modes show that the normal-mode frequencies increase under pressure. To establish the influence of vibrational anharmonicity on phonon dynamics, scattered wave displacement amplitudes have been calculated for the possible types of three-phonon interactions on the basis of first-order time-dependent perturbation theory.