Phase transitions in [N(CH3)4]2ZnCl 4 and [N(CH3)4]2CuCl4 crystals 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.