Study of the Ferroelastic Phase Transition of TlH<sub>2</sub>PO<sub>4</sub>Acoustic Phonon Softening
作者:Kazuhiro Hanazawa、Masaru Komukae、Toshio Osaka、Yasuharu Makita、Masazumi Arai、Toshirou Yagi、Akira Sakai
DOI:10.1143/jpsj.60.188
日期:1991.1.15
Elastic, thermal and dielectric measurements of TlH 2 PO 4 were carried out in a temperature range covering the upper phase transition point at 357 K. The specific heat shows a λ-type anomaly associated with the upper phase transition of second order and yields the transition entropy Δ S =1.46 J/mol·K. The elastic stiffness c 55 among c i i ( i =1, 2,···, 6) determined from the ultrasonic velocity
TlH 2 PO 4 的弹性、热和介电测量是在覆盖上相转变点 357 K 的温度范围内进行的。比热显示出与二阶上相转变相关的 λ 型异常,并产生转变熵 Δ S =1.46 J/mol·K。从频率为 10 MHz 的超声波速度数据确定的 cii ( i = 1, 2,..., 6) 中的弹性刚度 c 55 表现出很大的异常,并在上相变点处趋于接近零值. 结果表明,上部铁弹性相变是由 B 2g 横向声学模式的不稳定性引起的,铁弹性相变点附近的弹性、热和介电行为可以用唯象理论来合理解释。