TEMPERATURE-DEPENDENCE OF THE STATIC DISTORTION IN INCOMMENSURATE DISPLACIVE PHASES AND ITS EFFECT ON THE DIFFRACTION PATTERN .2. SATELLITEREFLECTIONS

The effect on satellite reflections of the temperature variation of th e static structural modulation in incommensurate phases is studied. A structural model is introduced that includes the anharmonicity describ ed by the soliton density and follows the assumptions and predictions of the Landau theory generalized to incommensurate phases. Within thes e premises, a simulation of the diffraction pattern as a function of t emperature of Rb2ZnCl4 has been carried out. It is shown that the inte nsity of satellites does not always decrease monotonically with their order and its temperature dependence varies, depending on the satellit e, so that it cannot be reduced to a common effective power law. Satel lites of first order, for instance, can decrease or increase near the lock-in transition, depending on the particular reflection considered. A simple method for measuring the soliton density is proposed that is based on the expected correlation of the intensities of close first-o rder and higher-order satellites. Finally, the effect that high-order harmonics can have in a standard refinement of an incommensurate struc ture near the lock-in transition is discussed.