Ferroelastic domain switching behaviour of [N(CH3)(4)](2)CUCl4 and [N(CH3)(4)](2)ZnCl4 single crystals studied by external stress

We studied the temperature dependence of the stress-strain hysteresis in [N (CH3)(4)](2)CuCl4 and [N(CH3)(4)](2)ZnCl4 single crystals grown by the slow evaporation method. From the obtained results, we determined that [N(CH3)( 4)](2)CuCl4 and [N(CH3)(4)](2)ZnCl4 single crystals have ferroelastic chara cteristics in phase IV and III, and phase V and IV, respectively. Also, the ferroelastic domain switching stress due to saturation effect is approxima tely 0.9 MPa in [N(CH3)(4)](2)CuCl4 and 0.4 MPa in [N(CH3)(4)](2)ZnCl4 crys tals. In order words, the ferroelastic phase transition due to external mec hanical stress applied to these crystals causes a transformation from the t win-domain state to the single-domain state.