Transmission electron microscopy study of B-site cation configurations in perovskite-structured Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 ceramics

Abstract

Configurations of B-site cations in the perovskite-structured ternary system Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-PbTiO3 (PMW-PNN-PT) of interest for multilayer ceramic capacitors were studied by transmission electron microscopy. The evaluated specimens were four PMW/PNN/PT compositions: 10/30/60, 30/30/40, 50/30/20, and 70/30/0 on a compositional line with 30 mol % PNN content. A ‘‘core-shell-type’’ microstructure was seen in the 10/30/60 specimen composition, which has a ‘‘normal’’ ferroelectric characteristic, along with typical ferroelectric domain structures. The B-site cation ordering in the 10/30/60 composition was not detectable in the selected-area electron diffraction pattern. On the other hand, an ‘‘island-type’’ microstructure, consisting of clusters (∼1–2 nm) with B-site cations 1:1 ordered, was observed in the 30/30/40, 50/30/20, and 70/30/0 compositions, which have relaxor-type characteristics. In the 70/30/0 composition, larger stripe-shaped ordered regions (∼20–200 nm) were also observed. These ordered regions extended from the center of the grain to the boundary. On the basis of the results obtained, origins of the dielectric behaviors for this system, that is, a ‘‘normal’’ ferroelectric, a relaxor ferroelectric, and an antiferroelectric, were discussed from the point of view of the B-site cation configurations. The PMW component plays two roles in this ternary system, corresponding to its content. When the PMW content is low, Mg and W ions are disordered in the B-site sublattice, and interrupt the ferroelectricity. With increasing PMW content, small ordered clusters (∼1–2 nm) are formed, which are believed to localize superparaelectric potentials effectively and dominate a degree of a diffuse phase transition in the solid-solution system.