Symmetry and Order Parameter of Antiferroelectric PbHfO3

On the bases of the result of X-ray diffraction at room temperature, the structure of antiferroelectric PbHfO3 has been studied in detail. For the paraelectric-antiferroelectric phase transition at 873K, the symme- try of antiferroelectric PbHfO3 is P2/m(C2i) . An axial vector R is selected as the order parameter to reflect the change of symmetry in antiferroelectric phase transition. According to Curie principle, the satisfying results are obtained relative to the change of symmetry group in the phase transition.