Domain Growth in Pb(Mg_1/3Ta_2/3)O₃ Perovskite Relaxor Ferroelectric Oxides

Extensive studies that have been conducted on the Pb(Mg1/3Nb2/3)O-3 (PMN) family of relaxer ferroelectrics have led to the establishment and acceptance of the "space-charge" model as a basis for explaining their structures and dielectric properties. In this model, the arrangement of the metal cations on the octahedral sites of the perovskite structure is interpreted in terms of the formation of negatively charged ordered nanodomains that are dispersed in a positively charged disordered matrix. The primary experimental support for this interpretation has come from the apparent absence of any growth of the domains or change in the degree of ordering as the heat treatment is extended, Here, we report on experiments that have been conducted on the tantalate relaxer, Pb(Mg1/3Ta2/3)O-3 (PMT), and its solid solutions with PbZrO3 in which the size of the domains and the degree of cation ordering have been increased by two orders of magnitude through annealing that has been conducted at a temperature of 1325 degrees C. Moreover, fully ordered ceramics that are comprised of large domains retain relaxer behavior, These results cannot be explained by the space-charge model and support a charge-balanced, "random-site" model for the ordering of the metal cations.