STRUCTURAL STUDY OF A TUNGSTEN BRONZE RELAXOR COMPOUND [PB2KTA5O15]

The structure of the tungsten bronze Pb2KTa5O15 relaxer above T-max wa s determined using X-ray and neutron diffraction data together. The Pb and K distributions have been determined. Moreover it was established that the Pb atom with 15 coordination sites are not on the special po sition (2mm) but distributed on two disorder positions. Preliminary re sults of a structural evolution are also presented. No phase transitio n was found as in the isotype compound Pb2KNb5O15. The diffraction pro files do not show significant evolution. It seems that there are no na nodomains similar to those of the PMN relaxer at low temperature.