SIMULATION OF THE TEMPERATURE DEPENDENCE OF THE Rb₂ZnCl₄ INCOMMENSURATE PHASE DIFFRACTION PATTERN. I. Aramburu, G. Madariaga^*, J. M. Pérez-Mato^*, Dpto. Física Aplicada I. Escuela Técnica Superior de Ingenieros Industriales y de Telecomunicación, Universidad del País Vasco, Alameda de Urquijo s/n, 48013 Bilbao, Spain, ^*Dpto. Física de la Materia Condensada, Facultad de Ciencias, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain

The temperature variation of the intensity of 1935 main reflections and 6991 satellites up to the 7^th order within the incommensurate phase of Rb₂ZnCl₄ has been simulated. The static structural modulation has been varied through the changes in 3 structural parameters: the amplitude of the primary mode, the soliton density and the amplitude of a third harmonic modulation. Contrary to what it is usually expected, the temperature dependence of main reflections shows a great variety of behaviours, due to the strong influence of the modulation first harmonic on some of them. In the case of satellites, the temperature variation of their intensities has been described through the "effective exponents" [[beta]]_n(T): I_n ~ t ^[[beta]]n(T), where t T - T_I. At every temperature, a great dispersion of values for the effective exponents of the satellites of the same order is obtained. This clearly prevents to obtain a direct information of the structural changes from the only knowledge of the [[beta]]_n(T) for some selected reflections, as it has been sometimes assumed. Besides, the average values obtained for these effective exponents at every temperature and for each satellite order do not satisfy the simple relation <[[beta]]_n> ~ n <[[beta]]₁>, either. Finally, the influence of the different distortions present in the static modulation on a standard refinement of the structure at a fixed temperature has been analyzed. In particular, it will be shown that the common assumption of taking as many harmonics in the structural modulation as the maximum order of satellites systematically measured may not always be the most appropriate.