Elastic Constants and Thermal Expansion of CsPbCl3

The sound velocities in perovskite-type CsPbCl 3 were measured around the three successive structural phase transition points at 37, 42, and 47°C using the ultrasonic pulse-overlap method. "Detwinned" samples were used, so that the measured velocities can be connected with the elastic constants in each phase. The results are analysed in terms of the phenomenological and fluctuation theories. In contrast to large critical anomalies in c 11 and c 12 in the cubic phase, the thermal expansion coefficient shows no corresponding anomaly even just above the cubic to tetragonal transition point. The measured elastic stiffness constants in the cubic phase at 50°C (80°C), in units of 10 11 dyn/cm 2 , are c 11 =2.95 (3.24), c 12 =1.60 (1.45), and c 44 =0.504 (0.509).