Ultrasonic investigation of antiferrodistortive phase transitions in betaine compounds

Abstract

The temperature dependencies of ultrasonic velocity and attenuation in deuterated betainie phosphite (DBPI) and its solid solutions with different content of betaine phosphate (DBP) are presented near the antiferrodistortive phase transitions. Measurements have been performed along all crystallographic X, Y and Z directions of the crystals. It was shown that the orientation dependencies of critical ultrasonic anomalies were different for pure DBPI and DBP crystals. In solid solutions DBPI/DBP orientation dependencies varied from those of DBPI to those of DBP. The ultrasonic experimental data in antiferrodistortive phase have been interpreted in terms of mean field Landau theory.