Mechanism of 1:1 nonstoichiometric short-range ordering in La-doped Pb(Mg1/3Nb2/3)O-3 relaxor ferroelectrics

The mechanism of the 1:1 nonstoichiometric short-range ordering in donor-doped Pb(B-1/3'B-2/3'')O-3-type relaxer perovskites was examined using the La2O3-doped Pb(Mg1/3Nb2/3)O-3 (PMN) system as a typical example. Based on the dielectric analysis and the transmission electron microscopy (TEM) observation, the observed increase in the degree of diffuse phase transition (DPT) in the presence of La2O3 was interpreted as the enhancement of the 1:1 nonstoichiometric short-range ordering accompanied with the growth of the negatively charged nanodomains. The mechanism of the defect process responsible for the 1:1 nonstoichiometric short-range ordering was elucidated by analyzing the electrical conductivity of the La-doped PMN system as a function of the partial pressure of oxygen. It was shown that the substitution of La3+ ions for Pb2+ ions in the A-site sublattice of perovskite PMN produced the positively charged La-Pb(.) sites with a concomitant generation of electrons for the electronic compensation. This expedites the growth of the nonstoichiometrically ordered nanodomains in a disordered matrix.