An expression for the sound velocity change in anharmonic BaxSr1-xTiO3 ferroelectric crystal is obtained in presence of an external electric field, by using double time temperature dependent Green's function technique. We have considered higher order anharmonic and electric moment terms in modified Silverman Hamiltonian for it. The field, defect and anharmonic contribution change in sound velocity are separately discussed. The sound velocity decreases anomaously in vicinity of the Curie temperature. The presence of higher order anharmonicity and electric moment decreases the sound velocity. It varies with temperature and sound velocity decreases with addition of defect in BaxSr1-xTiO3.
Greens function, Anharmonicity, defect, Ultrasonic velocity
