Anomalous behavior of phonon diffusiveness coefficient of cubic compounds with anomalous elastic properties

The phonon diffusiveness coefficient D related to scattering of phonons by point mass defects embedded in cubic crystalline media can be written as product of diffusiveness coefficient for a corresponding reference isotropic medium D-is, and the dimensionless coefficient (D) over tilde which depends on two dimensionless elastic parameters s(2), s(3). This coefficient is studied in. the triangle-shaped region of plane (s(2), s(3)) in which cubic elastic crystalline media care mechanically stable. As a function of s(2) and s(3) the coefficient (D) over tilde is nonmonotoneous and behaves singularly on the line s(2) = s(3) The underlying physical mechanism is considered.