Structure, stability, and dielectric properties of chemically ordered relaxors in the Pb(Mg1/3Ta2/3)O3–PbZrO3 (PMT–PZ) system

Abstract

The nano-scale phase separated domain structures of Pb(Mg1/3Ta2/3)O3 (PMT) relaxors are shown to be metastable and responsive to high temperature heat treatments. For pure PMT the 2–3-nm ordered domains in an as-sintered sample coarsen to approximately four times their original size (∼8 nm) after thermal annealing at 1325°C for 48 h. The alterations in the domain coarsening and degree of cation order are greatly enhanced in solid solutions of PMT with PbZrO3 (PZ). For 5–15 mol% substitutions fully 1:1 ordered microstructures comprised of ∼40-nm domains were stabilized after the same type of annealing. Quenching experiments revealed that the enhancements in the degree of order were related to a thermodynamic stabilization of the 1:1 order by the Zr cations. Models based on the random site description gave the most consistent interpretation of the cation ordering. The retention of a relaxor ferroelectric response in all the 1:1 ordered large domain PMT-PZ ceramics, indicates that randomness on one of the positions of the ordered structure, and not the chemical domain size, is the critical factor in inhibiting normal ferroelectric coupling.