The perovskite phase in PZN-PMN-PT pseudoternary ceramics was stabilized by the addition of excess constituent divalent oxides (PbO, MgO, and ZnO). 5 mol % excess MgO or 7.5 mol % excess PbO was sufficient to eliminate the remnant cubic pyrochlore phase after sintering at 1100 C C for 1 h. The enhanced diffuse phase transition (DPT) and the decrease in the electrical resistivity were observed in the presence of excess ZnO or MgO. These were interpreted in terms of the additional formation of negatively charged, short-range ordered 1:1 domains with a concomitant generation of charge carriers (holes). The behavior of excess MgO or ZnO at concentrations above 5 mol % was studied by examining complex impedance patterns.

The mechanism of the 1:1 nonstoichiometric short-range ordering in donor-doped Pb(B′1/3B″1/3)O3-type relaxor perovskites was examined using the La2O3-doped Pb(Mg1/3Nb2/3)O3 (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 sites with a concomitant generation of electrons for the electronic compensation. This expedites the growth of the nonstoichiometrically ordered nanodomains in a disordered matrix.

The diffuse phase transition (DPT) characteristics and the associated defect mechanism of Na-doped Pb(Mg1/3Nb2/3)O3 (PMN) relaxor perovskite were studied. The enhanced DPT and the decrease in the intensity of the superlattice reflection were observed in the presence of Na2O. These contradictory observations were interpreted in terms of the inhibition of the growth of the 1 : 1 nonstoichiometric short-range ordered domains and the increase in the microcompositional fluctuation of the B-site cations caused by the formation of negatively charged Na′Mg sites. The mechanism of the associated defect process was then elucidated by analyzing the electrical conductivity as a function of the oxygen partial pressure. It was shown that the substitution of Na+ ions for Mg2+ ions in the B-site sublattice of perovskite PMN produced the negatively charged sites with a concomitant generation of oxygen vacancies () for the ionic compensation. This expedites the enhancement of the compositional inhomogeneities of the B-site cations and suppresses the growth of the nonstoichiometrically ordered nanodomains in a disordered matrix.

Effects of thermal annealing on the dielectric/piezoelectric properties of Pb(Zn,Mg)1/3Nb2/3O3-PbTiO3 ceramics (PZMN-PT with Zn/Mg = 6/4) were examined across the rhombohedral/tetragonal morphotropic phase boundary (MPB). Examination of the lattice parameters and the rhombohedral angle indicated that the MPB is in the vicinity of 24 mol% PbTiO3. Both the relative dielectric permittivity (∊r) and the piezoelectric constant (d33)/electromechanical coupling constant (kp) were increased by thermal annealing (800–900 °C) after sintering at 1150 °C for 1 h. The observed improvements in the dielectric and piezoelectric properties were attributed to the elimination of PbO-rich amorphous intergranular layers (about 1 nm thickness) induced by thermal annealing. Both the dielectric analysis using the series mixing model and the microscopic examination by transmission electron microscopy supported this conclusion.

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(Mg 1/3 Nb 2/3 )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 Ni 2+ ions for Nb 5+ ions in the B-site sublattice of perovskite PMN produced Ni Nb ٟ sites with a concomitant generation of positively charged oxygen vacancies (V ⅐ ⅐ 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.