MICROSTRUCTURES OF PYROCHLORE-PEROVSKITE MIXTURES IN PBO-MGO-NB2O5 SYSTEM

Variation in Mg content lit the pyrochlore phase of composition Pb1.83 Mg0.29+xNb1.71-xO6.39-1.5x, where 0.1 less than or equal to x less tha n or equal to 0.522, resulted in the formation of PMN perovskite and w hen x=0.522, near pure perovskite phase was obtained. Sintering temper ature also played an effective role in the formation of perovskite in the pyrochlore. For small amounts of excess Mg, the perovskite general ly existed as inter- and intragranular inclusion particles with occasi onal clusters of perovskite grains, and when x greater than or equal t o 0.4, pyrochlore became the minor phase and perovskite formed the mat rix. Invariably, Mg rich phases were also observed in the microstructu re. Dielectric measurements sheaved that the relative permittivity of the mixtures increased with Mg concentration as a result of a decrease in the pyrochlore content. (C) 1997 The Institute of Materials.