Temperature anomalies in the dispersion and absorption of sound near phase transition points at low temperatures

We examined the attenuation and dispersion of sound during phase transitions with an overdamped soft mode at low temperatures. The obtained temperature and frequency dependences differ from results known at the high-temperature asymptote. The temperature anomalies are sharper. At low frequencies, the attenuation behaves like (T – T_c)^–5/2 for a critical phonon spectrum isotropic in k, and like (T–T_c)^–2 for uniaxial ferroelectrics. The presence of a temperature anomaly is characteristic also for high-frequency attenuation, behaving like (T–T_c)^–1/2 and ln(T–T_c)., respectively. We discuss briefly the results obtained from an experimental test.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 70–74, January, 1989.