Slowness surfaces study of the ferroelastic phase transition of LiCsSO4 crystal

The method of slowness surface is used to study the ferroelastic phase transition of LiCsSO₄. The slowness surfaces of the crystal have been plotted between 202K and 293K. The direction of the maximum slowness is on the XZ plane and the angle of it and X axis is -49.5 degree when temperature is above 206K. At 206K, the direction of the maximum slowness is along X axis. As the temperature decreases from 206K to 202K, the direction of the maximum slowness doesn´t change anymore but the slowness surfaces change dramatically. According to the soft mode theory and the elastic constitutive relations, we obtained that LiCsSO₄ crystal is in the same symmetry between 202K and 206K.