High-Order Diffraction Satellites and Temperature Variation of the Modulation in the Incommensurate Phase of Rb2ZnCl4

The intensity of a set of main reflections and satellites up to seventh order has been measured as a function of temperature within the incommensurate phase of ltb2ZnC14. The observed temperature dependence of the diffraction peaks can be explained by a variation of the static structural modulation through the changes in 3 parameters: the amplitude of the primary mode, the soliton density that describes its anharmonicity, and the amplitude of a third harmonic modulation. The eigenvectors of the primary mode and the third harmonic used for the static modulation have been derived from previously published structural data on the incommensurate and the ferroelectric structure. The soliton density behaviour, determined for the first time from X-ray diffraction data, agrees with results derived from other techniques.