Calorimetric investigations of overcritical behaviour in (TEA)(2)CuCl4 crystals

The results of experimental investigation of molar heat capacity of CN(C2H5 )(4)](2)CuCl4 - ferroelasto-ferroelectric crystals in a wide temperature ra nge are presented. The typical anomaly for the first order phase transition of order-disorder type at 258 K and additional anomaly with maximum at 195 K has been observed. We suggest that the low temperature anomalies of phys ical properties of [N(C2H5)(4)](2)CuCl4 crystals can be attributed to over critical traces of isomorphous phase transitions (similar to that observed in liquid-gas system). Results of numerical analysis of phenomenological mo del of phase transition in [N(C2H5)(4)](2)CuCl4 crystals are presented and compared with the experimentally determined temperature dependence of the s pecific hear and entropy changes.