Dielectric studies of ferroelectric phase transition in LNG crystal

The ferroelectric phase transition in LiNaGe4O9 crystal has been studied by means of classical macroscopic electric measurements. The obtained results are discussed within the frame of the classical dielectric state equation. It is shown that the classical P5-model can be applied only as a first approximation for the description of LNG critical behavior. The expansion coefficients of the state equation are estimated. The discrepancies between model and real behavior of the crystal have been observed close to the phase transition temperature for weak electric fields. It has been shown that the temperature dependence of dielectric constant, in a wide temperature range, can be described by a formula similar to that one resulting from the two-sublattice model proposed for LGO crystal.