DOI: 10.1051/jp1:1997150
J. Phys. I France 7 (1997) 371-383

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

I. Aramburu¹, G. Madariaga², D. Grebille³, J.M. Pérez-Mato² and T. Breczewski<sup>4

1</sup>  Departamento Física Aplicada I, Escuela Técnica Superior de Ingenieros Industriales y de Telecommunicación, Universidad del País Vasco, Alameda de Urquijo s/n. 48013 Bilbao, Spain
²  Departamento Física de la Materia Condensada, Facultad de Ciencias, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain
³  Laboratoire de Chimie-Physique du Solide UA 453, École Centrale, 92295 Châtenay-Malabry Cedex, France
⁴  Departamento Física Aplicada II, Facultad de Ciencias, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain

(Received 23 July 1996, received in final form 7 October 1996, accepted le 21 October 1996)

Abstract
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 Rb ₂ZnCl ₄. 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.

© Les Editions de Physique 1997