Thermally Induced Coarsening of the Chemically Ordered Domains in Pb(Mg1/3Nb2/3)O3 (PMN)-Based Relaxor Ferroelectrics

The effect of different tetravalent octahedral-site substitutions (M 5 Zr, Tb, and Ce) on the stability of the 1;1 chemically ordered phase in Pb(Mg1/3Nb2/3)O3 (PMN) relaxor ferroelectrics were investigated using X-ray diffractometry and transmission electron microscopy. In their as-sintered form, all the samples adopted a phase-separated microstructure that consisted of nanosized 1;1 ordered domains dispersed in a disordered matrix. However, after annealing at 1250°C for 24 h, a fully 1;1 ordered microstructure with large domains (>100 nm) was stabilized in 10 mol%-terbium-doped PMN. No ordered-domain coarsening was observed in pure or zirconium-doped PMN, which indicated that the size of the solid-solution additives was critical to stimulating the growth and stability of the 1;1 order. The observation of complete 1;1 order in the terbium-doped system supports the “random-site” model description of the Pb(b* 1/2b( 1/2)O3 structure. This model also can be used to explain the insensitivity of the diffuse frequency-dependent dielectric properties to the size of the chemically ordered domains.