ENHANCED DIFFUSE PHASE-TRANSITION AND DEFECT MECHANISM OF NA-DOPED PB(MG1 3NB2/3)O-3 RELAXOR FERROELECTRICS/

The diffuse phase transition (DPT) characteristics and the associated defect mechanism of Na-doped Pb(Mg1/3Nb2/3)O-3 (PMN) relaxer perovskit e were studied. The enhanced DPT and the decrease in the intensity of the superlattice reflection were observed in the presence of Na2O. The se contradictory observations were interpreted in terms of the inhibit ion of the growth of the 1:1 nonstoichiometric short-range ordered dom ains and the increase in the microcompositional fluctuation of the B-s ite cations caused by the formation of negatively charged Na-Mg' sites , The mechanism of the associated defect process was then elucidated b y analyzing the electrical conductivity as a function of the oxygen pa rtial pressure. It was shown that the substitution of Na+ ions for Mg2 + ions in the B-site sublattice of perovskite PMN produced the negativ ely charged Na-Mg' sites with a concomitant generation of oxygen vacan cies (V-O(..)) for the ionic compensation. This expedites the enhancem ent of the compositional inhomogeneities of the B-site cations and sup presses the growth of the nonstoichiometrically ordered nanodomains in a disordered matrix.