Structural aspects of ferroelectric phase transitions in the complex metal oxides A2Sb2O7 (A=Pb, Sr, Ca) with weberite structure

Neutron powder diffraction measurements of ceramic samples A(2)Sb(2)O(7) (A = Pb, Ca, Sr) with weberite structure have been carried out. The atomic arrangement has been determined at temperatures below and above T-c. using the Rietveld analysis in order to clarify the nature of ferroelectric ordering in this structural family. The displacement of A(2+) cations in its local environment probably causes the spontaneous polarisation in this structure. The transition temperatures appear to depend mainly on the nature of the A-cation ( ionic radius, valence). Thus the A-sublattice seems more likely to be the ferroelectrically active one.