Most of the physical properties of crystals which belong to the A2BX4 family, are closely connected with the growth method, and also with the thermal and mechanical treatments applied to the samples. It is the case for the dielectric response which shows a large thermal hystresis over a wide temperature range including the commensurate-incommensurate region.1,2,3) In this paper, we report the results of the dielectric measurements performed on Rb2ZnCl4 and (N(CH3)4)2ZnCl4 crystals (or TMA)2ZnCl4) grown by various methods, and propose an interpretation of the different observed behaviours, involving the presence of defects which appear during and after the crystal growth.