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.