ANOMALOUS BEHAVIOR OF SOUND NEAR CURIE POINTS IN DISPLACIVE-TYPE FERROELECTRICS

The dynamical behavior of the acoustic mode in displacive-type ferroelectrics such as BaTiO3and SrTiO3is studied theoretically. The phenomenological theory of sound attenuation near the phase transition point due to Landau and Khalatnikov is extended to the system in which kinetic energy plays an essential role, so as to be applicable to displacive-type ferroelectrics. The nature implied in the phenomenological theory is examined. The dependence of the attenuation constant and the velocity change of sound upon temperature and wave number is explicitly calculated on the quantum-statistical basis by employing the Silverman Hamiltonian. Thereby the occurrence of anomalies in both the attenuation constant and sound velocity near the Curie points is predicted. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.