Ferroelastic domain switching behaviors of superionic conductor M_3H(SO_4)_2 (M = K, Rb, and NH_4) single crystals

摘要

We have measured the temperature dependences of the optical polarizing microscopy and the stress-strain hysteresis curves in the K_3H(SO_4)_2, Rb_3H(SO_4)_2, and (NH_4)_3H(SO_4)_2 crystals grown by using the slow evaporation method. From these temperature dependences, it was determined that the three single crystals undergo the ferroelastic phase transitions near T_c. We also studied the ferroelastic domain switching that occurs in the three single crystals due to external mechanical stress. The critical stress values for switching from the ferroelastic twin domain to the paraelastic single domain were obtained. The ferroelastic domain switching stress of Rb_3H(SO_4)_2 crystals (0.7 MPa) was found to be higher than those of K_3H(SO_4)_2 and (NH_4)_3H(SO_4)_2 crystals (0.3 and 0.25 MPa, respectively). (NH_4)_3H(SO_4)_2 and K_3H(SO_4)_2 can therefore be more easily transformed by a weak external mechanical stress. This domain switching from the ferroelastic twin domain to the paraelastic single domain is explained by the restriction of the rotation of the SO_4 tetrahedron by the external stress.