Study of dielectric anomalies in Cu(HCOO)2· 4H2O and Cu(HCOO)2· 4D2O around their antiferroelectric phase transitions using pseudospin model

Abstract

Abstract Using two-sublattice pseudospin model and statistical Green's function techique, the anomalous dielectric behaviour in copper formate tetrahydrate (CFTH) and its deuterated form (CFTD) around their antiferroelectric (AFE) phase transitions have been studied. Expressions for the dielectric constant (e'), transition temperature (Tc) and the Curie-Weiss constant (C) have been derived. A single set of model parameters (like renormalized phonon frequency, tunneling frequency, pseudospin phonon interaction constants etc.), being different for different salts, have also been obtained from fitting of the experimental data for dielectric constants. The model parameters are used to calculate the transition entropy (ΔS) from Ps 2=(C/8τ)ΔS (where Ps is the sub-lattice polarization). These values of ΔS are found to be 0.67 and 0.81 cal/mole°C, respectively, for the CFTH and CFTD salts, which agree quite well with those available from experiment (viz. 0.78 and 0.90 cal/mole°C).