Defect and fluctuation effects at the incommensurate-commensurate phase transition in Rb2ZnCl4

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Abstract
The influence of defects and thermal fluctuations on the incommensurate-commensurate transition in modulated ferroelectric structures is studied. It is shown that the deviations near Tc from the equilibrium Landau theory can be understood in terms of an intermediate defect-dominated phase which they describe with a model of random internal fields. Choosing Rb2ZnCl4 as an example for quantitative comparison the authors use NMR, dielectric and X-ray satellite broadening data to evaluate the internal fields, the variation of the soliton density and the defect pinning energies. The roughness of the discommensuration walls in Rb2ZnCl4 is also estimated.