Ultrasound absorption in mercury telluride

Abstract

Measurements have been made of the attenuation of longitudinal and transverse ultrasonic waves in the frequency range 10 Mhz to 300 Mhz in single crystal mercury telluride between 1·2°K and 380°k for wave propagation along the [100], [111] and [110] crystallographic directions. The important ultrasound dissipation mechanisms include the viscous drag of lattice phonons and forced dislocation motion; thermoelastic and piezoelectric coupling losses are negligible. The lattice phonon-thermal phonon interaction at a given frequency is found to be large, owing to the low Debye velocity; the effect gives rise to a sharp attenuation increase approximately as the cube of the temperature above 20°K. A second loss mechanism arises from forced motion of dislocation segments. The frequency dependence of the decrement shows the maximum (at 190 Mhz) predicted by the Granato-Lucke theory of dislocation damping and the results have been accounted for by the vibrating string model. The damping coefficient B which describes the drag on a moving dislocation has been estimated as 2·3 × 10⁻⁵ dyn sec cm⁻² at 4·2°K and the effective loop length as about 3 × 10⁻⁴ cm. Data for the ultrasonic wave velocities and attenuation before and after annealing and under stress are in agreement with the dislocation mechanism. Bordoni-type relaxation peaks occur between 170°k and 260°k; the activation energy estimated from the Arrhenius relationship is (0·094 ± 0·004) ev and the attempt frequency is (4 · 1) × 10⁹ HZ. The low value of the Peierls stress (about 3 × 10⁷ dyn cm⁻²) calculated from the experimental data casts doubt on the applicability to compounds of the Seeger interpretation of the peaks.