Anisotropy of acoustic and thermal expansion properties of TlInSe <sub/>2</sub> crystals

摘要： Based on experimental studies of acoustic wave velocities in TlInSe2 crystals, all components of their elastic stiffness and compliance tensors are determined. TlInSe2 has three acoustic axes parallel to the principal crystallographic directions. The lowest velocities of acoustic eigenwaves are used to estimate the acousto-optic figure of merit. We analyse deviations from purely longitudinal and transverse polarization states, as well as the obliquity of acoustic energy flow. Temperature dependences of strains along the three principal crystallographic directions and of acoustic wave velocities v11, v22 and v33 are measured. Anomalous behaviour of these parameters occur at T1≈245 K and T2≈145 K. It is shown that the symmetry of TlInSe2 becomes lower than tetragonal below the temperature point T1.