Order-Disorder Phenomenon in Lead Scandium Tantalate

Lead scandium tantalate (PST) is a ferroelectric relaxor with the perovskite structure of A(B'B")O₃. By suitable heat treatment, the B-site cations can be brought from a stucturally disordered state into various degree of ordering. The degree of ordering is strongly affected by the amouth of vacancies present in the materials. To suppress PbO loss during the sintering or annealing process, a PbO-rich atmosphere is supplied by materials having high PbO vapor pressure, such as PbZrO₃. For PST ceramics with nearly zero weight loss, very long annealing times and higher annealing temperatures are required for ordering. The higher Pbo-loss materials are found to be easily ordered. The introduction of a reducing atmosphere during annealing enhances the ordering process. The ordering process is characterized quantitatively by X-ray diffraction and qualitatively by Raman spectroscopy.