X-Ray Study on the Thermal Hysteresis of the Modulation Wavevector in (Rb_1−xK_x)₂ZnCl₄

Abstract

The modulation wavevector (Remark: Graphics omitted.) exhibits remarkable thermal hysteresis over a wide temperature range including the incommensurate-commensurate transition point in the mixed crystal system (Rb_1−xK_x)₂ZnCl₄ with x=0, 0.005, 0.02, 0.28, 0.92, 0.997 and 1. This hysteresis seems to correspond to the thermal hysteresis observed in the dielectric constant and to support the proposal by Hamano et al. that the pinning of the modulation wave by defects causes the hysteresis. In the Rb rich case (x≤0.02), the parameter δ has a tendency to be fixed to the value realized at the normal-incommensurate transition point. In the K rich case (x=0.997), it decreases monotonically with decreasing temperature, with a plateau in a middle range of the incommensurate phase. In the middle range of x, δ is pinned to a constant value down to low temperature.