X-Ray and Dielectric Studies of Commensurate-Incommensurate Phase Transition in Rb₂ZnCl₄

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The commensurate (C)-incommensurate (IC) phase transition in Rb₂ZnCl₄ has been investigated through studies of the X-ray diffraction and the P-E hysteresis loop. Simultaneous observation of the P-E hysteresis loop and the misfit parameter reveals that the double hysteresis loop observed in the IC phase corresponds to the field induced C–IC transition. The “triple”-like hysteresis loop observed in the vicinity of the C–IC phase transition temperature corresponds to the coexistence of the IC and the C state near E=0 followed by the field induced C–IC transition at a finite value of E. The effect of pinning on the electric field dependence of the misfit parameter and the polarization is considered on the basis of the Landau type theory. The tendency of the calculated results agrees well with that of the experimental results.