Effect of ordered vacancies on ultrasonic wave propagation in some mercury-indium tellurides

Abstract The compounds HgTe, Hg 5 In 2 Te 8 and Hg 3 In 2 Te 6 constitute a series in which the concentration of vacancies, sited regularly on the lattice array, increases progressively from zero. To assess the effect of vacancies on the mechanical properties the propagation of 10 MHz ultrasonic waves has been studied in these compounds. The elastic constants show a regular trend through the series, namely that the stiffness decreases as the vacancy concentration increases. In particular, the reduced bulk modulus is found to be directly proportional to the number of vacancies present. Bordoni-type relaxation peaks occur in all three compounds and are consistent with dislocation motion on the {111} and {110} slip planes. The activation energies for kink formation and the Peierls stresses, calculated on the basis of the kink nucleation theory, show that dislocation motion becomes easier with increased vacancy concentration and takes place more readily on the {111} slip planes.