Mechanism of 1:1 nonstoichiometric short-range ordering in La-doped Pb(Mg 1/3 Nb 2/3 )O 3 relaxor ferroelectrics

The mechanism of the 1:1 nonstoichiometric short-range ordering in donor-doped Pb(B{sub 1/3}{sup {prime}}B{sub 2/3}{sup {double_prime}})O{sub 3}-type relaxor perovskites was examined using La{sub 2}O{sub 3}-doped Pb(Mg{sub 1/3}Nb{sub 2/3})O{sub 3} (PMN) system as a typical example. Based on the dielectric analysis and the TEM observation, the observed increase in the degree of diffuse phase transition (DPT) in the presence of La{sub 2}O{sub 3} was interpreted as the enhancement of the 1:1 nonstoichiometric short-range ordering accompanied with the growth of the negatively 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 La{sup 3+} ions for Pb{sup 2+} ions in the A-site sublattice of perovskite PMN produced the positively charged La{sub Pb}{sup .} sites with a concomitant generation of electrons for the electronic compensation. This expedites the growth of the nonstoichiometrically ordered nanodomains in a disordered matrix. {copyright} {ital 1997 Materials Research Society.}