Processing and characterization of lead magnesium tantalate ceramics

Using a processing route that employed platinum crucibles, single phase ceramics of Pb(Mg1/3Ta2/3)O-3 (PMT) relaxer ferroelectrics were prepared with densities greater than 95% of their theoretical value. The improvements in the sintering characteristics of this system that result from this route were reflected by the dielectric properties, epsilon(max)' = 6300 at 182 K, which are similar to those reported for single crystal PMT. Contrast originating from nanosized polar clusters was evident in dark-field TEM images collected from the PMT ceramics at room temperature and showed little change upon cooling through the permittivity maximum. The electron diffraction patterns contained weak superlattice reflections at (h +/- 1/2, k +/- 1/2, l + 1/2) that originate from a 1:1 ordering of the B-site cations. High resolution imaging indicated that the length scale of the chemical ordering in PMT is essentially identical to niobate relaxers such as PMN, with the 1-2 nm ordered domains being surrounded by a disordered matrix.