Ordering Structure and Dielectric Properties of Undoped and La/Na‐Doped Pb(Mg1/3Nb2/3)O3

Abstract

Transmission electron microscopy was used to study the ordered domain structures in undoped and La/Na‐doped Pb(Mg1/3Nb2/3)O3 (PMN), where the compositions of the doped samples were specifically chosen so as to elucidate the ordering mechanism. The results showed that the Mg2+ ions and Nb5+ ions are short‐range ordered on the B‐site sublattice in undoped PMN, with a domain size of 2 to 5 nm. This short‐range ordering gives rise to B‐site composition fluctuations occurring on a nanometer scale, and it is this compositional inhomogeneity which is believed to be responsible for the diffuse phase transition behavior. Donor doping with La2O3 can compensate for the local charge imbalance resulting from the short‐range order and thus enhances the degree of ordering. Acceptor doping with Na2O, however, increases the charge effect, and hence ordering is suppressed. The effect of Na doping and La doping on the dielectric properties of PMN is also discussed.