The Effect of Doping and Composition on the Dielectric Properties and Sintering of a Lead Magnesium Niobate-Lead Titanate-Based Ceramic Dielectric Composite

A series of lead magnesium niobate-lead titanate ((1-x)Pb(Mg _1/3Nb _2/3)O₃-xPbTiO₃) relaxor ferroelectrics (PMN-PT) are being used in the composite design of a stable high temperature high permittivity ceramic dielectric. However, pure PMN has a dielectric maximum no lower than -10degC. To extend this range to lower temperatures niobium was replaced with tantalum. The tantalum-based component (PMTa-PT) is more refractory and does not sinter as easily as the PMN-PT components of the dielectric composite. The effect of lead oxide and lithium oxide as sintering aids was explored. Both dopants enhanced the sinterability of the tantalum-based component, while the lead oxide reduced its permittivity. At compositions above 0.70PMN-0.30PT, PMN-PT becomes less relaxor-like limiting the design of the stable dielectric to 140degC. To extend this range to higher temperatures a composite approach was taken. A series of four compositions between 0.63 to 0.65 PMN-PT was fabricated. Trilayer composites were made from these compositions with 0.70PMN-0.30PT. By varying the thickness of the composite layers an optimal configuration for the high-temperature component of the composite dielectric was determined which extended the dielectric stable temperature range of the composite dielectric to 185degC.