Structural models for lead magnesium niobate

Structural models for the low and high temperature phases of lead magnoniobate, Pb(Nb2/3Mg1/3)O-3 (PMN), are proposed. Two structural types, belonging to space group Pnma (S.G. Nr. 62) and Cmcm (S.G. Nr. 63), have been identified for the low and high temperature PMN phases. Simulations based on these structural types yield superlattice reflections in good agreement with those recently reported Zhang and coworkers [10]. Disorder effects related to the intergrowth of pseudo-rhombohedral and orthorhombic phases, are included in the model by increasing the symmetry of the tetragonal phase, which resulted in a pseudo-cubic structure consistent with the observed superlattice reflections. (C) 1997 Elsevier Science Ltd.