Rhombohedral to cubic phase transition in the relaxor ferroelectric PZN

The structure and phase transition in lead zinc niobate (PZN) were studied using very high resolution powder neutron diffraction between 4.2 and 450 K. The structure is unequivocally rhombohedral in space group R3m with a = 4.060 48 angstrom and alpha = 89.8693 degrees at 4.2 K. No low symmetry phases were observed, nor was an octahedral tilting transition to R3c as occurs in some parallel systems (e.g. PZT). Within the rhombohedral structure, large average ion displacements were found relative to the rather small spontaneous strains. On heating, a transition to a cubic perovskite occurs, with a critical temperature of similar to 384 K.