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.
X-Ray Study of LiCsSO 4 in Connection with Its Ferroelastic Phase Transition
The crystal structure of LiCsSO 4 was studied at 25, 0, -20 and -40°C in the normal phase and -71, -78 and -100°C in the ferroelastic phase by using X-ray reflection data collected by an automatic four circle diffractometer. The librational motion of SO 4 is highly anisotropic in the high temperature phase. Temperature variation of the atomic position of S or O atoms was small in the low temperature phase. The mutual proportionality between the temperature dependence of observed structure factors of reflections 201, 203, 205, 311 and 131 and that of the deviation angle Δ γ of the monoclinic angle γ from 90° was found, which suggests that the phase transition is characterized by the order-disorder nature of the SO 4 ion coupled with the shear strain x 6 .
Acoustical studies of LiKSO4, K4LiH3(SO4)4, and LiCsSO4 crystals
Abstract Results of ultrasonic study of LiKSO4 crystals in the range of high temperature phase transitions, K4LiH3(SO4)4 crystals above room temperature and LiCsSO4 crystals in the whole range of the low temperature pseudoproper ferroelastic phase transition are reported.