Abstract
A high-resolution synchrotron diffraction study of the temperature dependence of thestructures of the two layered Bi oxides PbBi2Ta2O9 (PBT) and PbBi2Nb2O9 (PBN)is reported. The transition from the low-temperature orthorhombic ferroelectricstructure to the high-temperature tetragonal paraelectric structure in PBN involvesan intermediate orthorhombic paraelectric phase. We conclude that this has the sameAmamstructure as observed in SrBi2Ta2O9 and its Bi-rich analogue. Identifying thesequence of phase transitions in PBT is more challenging since above 200 °C thestructure is metrically tetragonal within the resolution of the synchrotrondiffraction measurements. By contrast, neutron diffraction measurements suggestthat PBT remains orthorhombic to above the Curie temperature ≈430°C. The possible identity ofthe intermediate space group is discussed.
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