布里渊散射研究K_2SnCl_6晶体的弹性常数和声学模软化

Elastic constants and softening of acoustic Mode in K_2SnCl_6 crystal studied by Brillouin scattering

本文测量了六卤素金属化合物六氯锡钾室温布里渊散射纵声速和横声速。计算了晶体的弹性常数、折射率、体积压缩系数。并进一步研究了[111]方向声子的纵声速随温度的变化关系,发现当温度从高温降到256K附近,C_(11)+2C_(12)发生突变。利用Pippard关系进行了分析,得出晶体在T=256K附近发生一级相变。这种声学反常行为可以用均匀弹性应变场与软模坐标涨落的非线性耦合来解释。

Room-temperature Brillouin-scattering measurements of the longitudinal and transverse sound velocities for the hexahalometallate K2SnCl6 are presented. The elastic constants, refractive indices, volume compressibility are determined from the Brillouin line shifts. Furthermore, the sound velocity in the [111] -direction is investigated as a function of temperature in the range 252 K-270 K. An acoustic abrupt change of the Cu+2C12 mode is observed as the temperature approaches 256 K from above. This has been analysed using the Pippard relations. The conclusion is that this acoustic anomaly may be interpreted by nonlinear coupling of the elastic strain field to the fluctuation of the soft-mode coordinate.