Third-Order Elastic Constants in a Critical Region of Temperature

用改进的Stockbarger法生长了钙钛矿型晶体CsPbCl_3单晶。在本研究中获得了两个约1立方厘米的立方体样品。本文用脉冲回波重叠法测量了CsPbCl_3在超高压下的超声波声速。用基频为10 MHz的石英换能器产生纵模或横模超声波，由声速的压力导数导出了47-100 ℃范围内的三阶弹性常数C_<111>+2C<112>_、C_<111>-C_<123>和C_<144>+2C_<166>的组合，发现C_<111>+2C_<112>和C_<111>-C_的温度依赖性存在临界反常<123>。结果表明，序参量涨落是导致三阶弹性常数异常的主要原因。

Single crystals of perovskite-type crystal CsPbCl_3 were grown by the modified Stockbarger method. Two cubic samples of about 1 cm^3 were obtained in the present study. Ultrasonic wave velocities of CsPbCl_3 have been measured above the cubic-tetragonal phase trnsition temperature under hydrostatic pressure by the pulse-echo overlap method. Ultrasonic waves of the longitudinal or the transverse mode were generated by quartz transducers of fundamental frequency of 10 MHz.The combinations of third-order elastic constants C_<111>+2C_<112>'C_<111>-C_<123> and C_<144>+2C_<166> were deduced from pressure derivatives of the sound velocity over the temperature interval 47-100ﾟC.Critical anomalies were found in the temperature dependence of C_<111>+2C_<112> and C_<111>-C_<123>. It has been revealed that the order-parameter fluctuation is responsible for the observed anomaly in the third-order elastic constants .