Specific heat anomalies in ferroelectrics LiNaGe4O9 and Li1.1Na0.9Ge4O9

The heat capacity of LiNaGe4O9 and Li1.1Na0.9Ge4O9 crystals has been measured using AC calorimetry method. It is shown, that the temperature evolution of the excess heat capacity and the excess entropy of both crystals, in the ferroelectric phase, can be described by the formulas resulting from the classical Landau theory of phase transition. The values of the Landau expansion coefficients are determined. The obtained results lead to the conclusion that the spontaneous polarization can be reckoned as an order parameter in the phase transition of the weak ferroelectric LiNaGe4O9. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.