Superstructure and disorder in layered lead oxychlorides

We propose to study the relationship between short-range and long-range order in some layered lead oxychlorides characterized by a high degree of static disorder. The phases, consisting of layers of edge-sharing OPb4 tetrahedra alternated by Cl sheets, have a general formula Pb7XO8Cl2 with X= I, MO, As, V, Si. Single crystal X-ray diffraction (SC-XRD) data obtained with laboratory instruments and preliminary XAS data obtained on BM08 “LISA” at ESRF suggest that the lack of long-range ordering associated with the substitution of Pb by the X cations is related to a disordered occurrence the cavities hosting these elements within the OPb4 layer and/or to a disorder in the layer stacking. The superstructure and the correlated disorder of the structure could be analysed and understood with a precise diffraction measurement and a diffuse pattern mapping.