A new mechanism of nonstoichiometric 1 : 1 short-range ordering in NiO-doped Pb(Mg1/3Nb2/3)O-3 relaxor ferroelectrics

Abstract

A new mechanism of the nonstoichiometric, 1:1 short-range ordering, which leads to enhanced diffuse phase transition (DPT), was proposed and tested using NiO-doped Pb(Mg1/3Nb2/3)O-3 as a model system for Pb(B-1/3'B-2/3")O-3-type relaxor ferroelectrics. The enhanced DPT and the increase in the intensity of {h+1/2,k+1/2,l+1/2}-type superlattice reflection both were observed in the presence of NiO. These observations were interpreted as the increase in the number density of the short-range-ordered nanodomains without the domain growth. The mechanism of the atomic defect responsible for the increase in the number density of the 1:1 ordered nanodomains was investigated by analyzing the electrical conductivity as a function of the partial pressure of oxygen. It was shown that the substitution of Ni2+ ions for Nb5+ ions in the B-site sublattice of perovskite PMN produced Ni-Nb" sites with a concomitant generation of positively charged oxygen vacancies (V-O(..)) for the ionic-charge compensation. This defect process will stabilize the negatively charged nonstoichiometric 1:1 short-range-ordered domains and, thus, increase the number density of the ordered nanodomains in a disordered matrix.