Discovery of difference in the diffuse scattering from nonstoichiometric Ca 0.87 La 0.13 F 2.13 and Ca 0.92 Er 0.08 F 2.08 crystals with different types of clusters of structural defects

A new approach to application of diffuse scattering (DS) for studying the defect structure of crystals on laboratory radiation sources is implemented. The basic principles of this approach are as follows: (i) choice of crystals with a high concentration of structural defects (highly nonstoichiometric Ca 1 − x R x F 2 + x phases), (ii) application of intermeasurement minimization method (experimental comparison) to select a weak desired DS signal from a superposition of signals of different nature, and (iii) choice of the basic model proceeding from the reliable information provided by accurate analysis of the contribution of structural defects to Bragg reflections. Significantly different DS diffraction patterns have been recorded for Ca 0.87 La 0.13 F 2.13 and Ca 0.92 Er 0.08 F 2.08 crystals, characterized by different types of structural-defect clusters, determined from the Bragg diffraction data. Experiments performed at 90–100 K proved that DS is caused by clusters with stable atomic configurations rather than cooperative thermal atomic vibrations. A set of methods is proposed which can efficiently be used in diagnostics of nanomaterials.