A phenomenological study on ferroelastic KH3(SeO3)2 and KD3(SeO3)2

Abstract

The anomalous behavior of the Brillouin frequency shift ω of the soft acoustic mode for KH3(SeO3)2 and KD3(SeO3)2, and also the volume thermal expansion ∝V and the specific heat Cof KH3(SeO3)2 have been analyzed for various temperature intervals close to the phase transition temperatures TC at around 211 K and 302 K, respectively. Our extracted values of the critical exponent from C and ∝V of KH3(SeO3)2 within the temperature intervals of |T−TC|<7K are nearly zero, while the critical exponent extracted from the Brillouin frequency shift data of both KH3(SeO3)2 and KD3(SeO3)2 within the same temperature interval of |T−TC|<7K decrease very rapidly toward to zero as the phase transition temperatures are approached. Our results indicate that the critical behavior of ω, ∝V and C of both KH3(SeO3)2 and KD3(SeO3)2 can be described with the same critical exponent within the temperature interval of |T−TC|<2K.