Acoustic phonons in cubic media: properties of their polarizations and of the diffusion coefficient

摘要

In terms of every's elasticity parameters the stability region of cubic media has the form of wedge (s_1 > 0) with triangular cross-section in the (s_2, s_3) plane. This stability triangle can be divided into four regions, one of them is newly introduced, in which polarizatons of long wavelength acoustic phonons behave quite differently. In three of them polarization properties of modes are anomalous. To achieve detailed specification of these anomalies we performed vast numerical calculations and devised new characteristics, namely the polarization indicators, surfaces of polarization angles and maps of polarization enhancement factors. The diffusion coefficient D related to elastic scattering of phonons by point mass defects is influenced by these anomalies. Properties of D are considered on the whole stability triangle. Calculating D we account for anomalous properties of Debye's velocity near the stability borders.