SURFACE EFFECT ON THE SOFT ACOUSTIC MODE OF KD3(SEO3)2 STUDIED BY MICROPROBED BRILLOUIN-SCATTERING

By the use of a nicroprobed Brillouin scattering system, theraally excited acoustic modes i n a ferroelastic KD3(Se03)2 crystal have been observed as a function of depth from the surface. Both a longitudinal aode c22 and a transverse soft node c44 propagating along the (0101 direction becone hard as the observation area closes t o the (110) surface just above the transition temperature. Especially, the transition temperature at the surface, determined as the minimum position of the frequency shift of the soft acoustic c44 mode, shifts to lower side by about 0.1 K. I t is concluded t h a t the soft acoustic mode associated with the bulk ferroelastic phase transition is modified near the surface. On the other hand, these modes do not show any drastic anomaly near the (001) surface. A configuration effect is suggested between the surface and the propagation direction of the acoustic modes. © 1990, Taylor & Francis Group, LLC. All rights reserved.