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 and optical study of the phase transition in LiCsSO4
Abstract Lattice parameters of LiCsSO4 have been measured in the temperature range 160–550 K with an X-ray single-crystal Bond diffractometer. The monoclinic angle γ in the low-temperature ferroelastic phase has been interpreted as an order parameter. Detailed results of X-ray studies of the ferroelastic domain structure supported by observations under a polarizing microscope are presented. An earlier report on the existence of an intermediate phase in LiCsSO4 has not been confirmed.
Acoustic Studies of LiKSO4 Crystals in the 290 to 930 K Region
The temperature dependence of velocity and absorption coefficient of longitudinal and transverse acoustic waves are studied for LiKSO 4 crystals within the temperature range 290 to 930 K. Anomalies in the velocity and absorption values are detected near 708 and 743 K. The observed considerable hysteresis of velocity for the longitudinal wave propagating along the y-axis of the hexagonal structure at room temperature, suggests the presence of an intermediate incommensurate phase. A similar hysteresis was also observed for the transverse wave, propagating along the x-axis and polarized along the y-axis