BRILLOUIN-SCATTERING STUDIES OF K2ZNCL4 (100-300 K)

High resolution Brillouin spectroscopy has been used to study the elas tic properties of K2ZnCl4 crystal in the temperature range from 100 to 300 K in order to establish the temperature behaviour of elastic stif fness tensor components. Ten Brillouin modes have been observed for th e phonons propagating in the six directions. All phonon velocities rev eal different anomalies at the phase transition (T-0 = 144.7 K). The o btained results allowed a calculation of the temperature dependence of elastic constants of the prototype phase. A comparison of the present ed results with the earlier low-frequency data indicates a strong rela xational character of the order parameter in K2ZnCl4 and the anomalous dispersion behaviour of quasilongitudinal and quasitransverse phonons propagating along the [110] direction.