PRESSURE AND TEMPERATURE-DEPENDENCE OF THE ELASTIC PROPERTIES IN AL-MN-PD QUASI-CRYSTAL

In icosahedral quasi-crystals the second-order elastic constant tensor is known theoretically and experimentally to be isotropic; however, elastic isotropy does not hold if higher-order elasticity tensors are considered. In particular the stress dependence of sound velocities which involves at least a sixth-rank tensor is expected to be anisotropic in quasi-crystals. In this paper, the pressure dependence of sound velocities is calculated for both longitudinal and shear ultrasonic waves propagating in an icosahedral structure and the first measurements of sound velocities in a quasi-crystal under pressure are reported; the longitudinal and shear waves velocities are also measured from 4 to 300 K. The temperature dependence of sound velocities confirms the elastic isotropy, while the pressure dependence exhibits an unusual behaviour.