Near-phase pure perovskite lead magnesium niobate (PMN) with MgO or PbO additives was produced by reacting PbO with MgNbzOs at 800°C and sintering at 1200°C. Dense ceramics were characterized by scanning electron microscopy, X-ray diffraction, and dielectric measurements. The microstructural studies showed that excess MgO exists as micrometer spherical particles either in the grain boundary as a discrete particle or in the perovskite grain as an inclusion. The pyrochlore phase exists in large isolated grains in the microstructure. The 10 mol% MgO excess composition had a peak dielectric constant of 19500 at 100 Hz, which suggests very "clean" or uninhibiting grain boundaries. The excess addition of PbO did not improve the yield of perovskite PMN phase and decreased the dielectric constant. PMN grain boundaries are the dominant path of fracture. This paper, to a certain degree, explores the chemistry and characteristics of these grain boundaries. [
Lead scandium tantalate (PST) is a ferroelectric relaxor with the perovskite structure of A(B'B)03. By suitable heat treatment, the B-site cations can be brought from a structurally disordered state into various degree of ordering. The degree of ordering is strongly affected by the amount of vacancies present in the materials. To suppress PhO loss during the sintering or annealing process, a PbO-rich atmosphere is supplied by materials having high PhO vapor pressure, such as PbZr03. 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. [
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