Temperature anomalies of the sound velocity and attenuation in structural phase transitions at low temperatures

Correction formulae to elasticity complex modulus are obtained in terms of model which takes into account interaction of acoustic wave with soft mode responsible for structure phase transition. In contrast to published results valid in high-temperature approximation for crystal lattice, calculations in this paper are conducted in low-temperature asymptotics. It is shown that the recent experimental data on temperature anomalies of sound velocity and of attenuation coefficient at structure phase transitions, which accompany superconducting transition in ceramics, may be explained in terms of low-temperature approximation. Detail comparison of the effort results with experimental data is conducted, temperature ranges, where the acquired theoretical formulae agree well with the experiment, are revealed. Conclusion is made, that soft mode responsible for structural transition in lanthanum ceramics, is, apparently, of overdamping character