Ordering of Mg and Nb in the octahedral positions of the “cubic” perovskite structure of Pb3MgNb2O9

Abstract

Abstract Selected-area electron-diffraction patterns and x-ray diffraction powder patterns were taken of crushed single crystals of Pb3MgNb2O9. Although the x-ray patterns did not indicate any deviation from the cubic perovskite structure, the single-crystal electron-diffraction patterns showed additional spots which were attributed to a superlattice. Those superlattices which are compatible with the experimental data were derived. The diffuse phase transition of Pb3MgNb2O9 and the direction in which the spontaneous polarization occurs may be explained by the proposed B-site ordering.