SOUND ATTENUATION IN FERROELECTRIC SOLIDS

Abstract
An expression for the sound-attenuation constant in doped displacive ferroelectrics, in the presence of an external electric field, is obtained by using the double-time thermal- Green's -functions technique. The mass and force constant changes between the impurity and the host lattice atoms are taken into account in the Silverman Hamiltonian augmented with higher -order anharmonic and electric-moment terms. The defect-dependent, electric- field-dependent, and anharmonic contributions to the attenuation constant are discussed seperately. An anomalous increase in the attenuation constant is predicted in the vicinity of the Curie temperature. The soft mode is held responsible for this effect. The effect of defect, anharmonicity, and electric-field parameters on the stabilization of the soft mode frequency is also studied.