Landau behaviour of the ferroelectric phase transition in RbH₂PO₄

Abstract The ferro-paraelectric phase transition in Rubidium di-Hydrogen Phosphate, has been analysed using the Landau Theory. Birefringence, Thermal Expansion and AC Calorimetric measurements around the transition temperature together with previous data, have provided the necessary experimental information for a thermodynamic description of this phase transition within the classical frame. The values of the phase transition thermodynamic functions (ΔH =118 cal/mol and ΔS = 0.811 cal/mol.°C) are similar to those found in KDP and the specific heat behaviour around the Curie temperature excludes any noticeable contribution from the order parameter critical fluctuations.