Diffusion of phonons in cubic media with elastic anomalies

摘要

Elastic properties of cubic media are characterised by three elastic parameters: s_1, s_2 and s_3 introduced by Every. For semiconductor alloys exhibiting non-stoichiometrically driven valence fluctuations and semiconductor-to-metal phase transition the difference #epsilon# = (s_2 - s_3) is small. Such compounds show several elastic anomalies. We study the diffusion of long-wavelength acoustic phonons due to elastic scattering by point mass defects. For small #epsilon# the phonon conversion processes are weak by comparison with processes which randomise the directions of wave vectors. For such values of #epsilon# we calculate the phase, group velocities and diffusion constant. On the line s_2 = s_3 the diffusion constant is anomalously large and when s_2 = s_3 -> it becomes singular.