ELASTIC BEHAVIOR OF RBHSEO4 AT THE SUPERIONIC PHASE-TRANSITION INVESTIGATED BY BRILLOUIN-SCATTERING

Brillouin investigations have been performed over the temperature rang e 160-200 degrees C, which includes the superionic phase transition ne ar similar to 178 degrees C. Strong discontinuities are obtained for t he three elastic constants C-11, C-22 and C-33 at the superionic trans ition. In the superionic phase, two longitudinal Brillouin doublets ca n be observed for every direction of the acoustic wave vector. This fa ct can be attributed to the presence of two kinds of regions above the transition. Besides, systematic broadenings of these longitudinal lin es are observed in the superionic phase. The results are qualitatively discussed in connection with theoretical expectations.