We present the first low frequency (0.1-20 Hz) measurements of the complex elastic constant on KSCN single crystals. Our measurements show very slow sample-size dependent elastic relaxations, at temperatures ranging from $T_c-40\mathrm{}$ K up to the order-disorder phase transition temperature $T_c$. The data can be well explained with the assumption of temperature or equivalent entropy fluctuations. This phenomenon, although intimately related to the thermal-diffusion central peak phenomenon is, to our knowledge, for the first time seen in a macroscopic elastic susceptibility.

• Received 27 April 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.2575