Phase Transitions in [N(CH3)4]2ZnCl4and [N(CH3)4]2CuCl4Crystals Related with the Incommensurate Modulation Existence

Abstract

The continuous phase transitions are observed in the crystals with incommensurate phase. They are transitions of parent–incommensurate phases (Ti); transitions between metastable states; incommensurate–commensurate phases (Tc). It was set that phase transition between parent and incommensurate phase is a continuous second-order phase transition with a critical index β = 0.5. The transition between metastable states is a continuous phase transition through the intermediate temperature region — incommensurate phase. The wave vector changes with the temperature here and wave vector q∗ = q1 − q2 appears, where q1, q2 denote commensurate values of incommensurability wave vector of neighboring metastable states. It was shown that the phase transition between incommensurate and commensurate phases is a continuous phase transition.