Impacts of A-Site Dopants on the Local Structures and Macroscopic Properties of PMN Relaxor Ferroelectrics

Lead-based relaxor ferroelectrics are attractive for applications ranging from ultrasound imaging to underwater actuators, owing to their outstanding dielectric and piezoelectric properties. However, the relationship between nanoscale structural heterogeneities and relaxor characteristics (i.e., dielectric relaxation and diffused phase transition) remains disputed. Some studies suggest the relaxor behavior in Pb(Mg_1/3Nb_2/3)O₃-based relaxor ferroelectric is linked with nanoscale polar structures originating from short-range chemical order. While others propose that no spatial correlations exist between chemical order and polar nanoregions. Here, we modulate the chemical order in Pb(Mg_1/3Nb_2/3)O₃ through doping and characterize the corresponding dielectric and ferroelectric properties. It is found that the B-site cation order in Pb(Mg_1/3Nb_2/3)O₃ can be enhanced or suppressed by the introduction of La³⁺ or Na⁺, respectively, however, no apparent correlations are found between the chemical order and relaxor character, including permittivity dispersion, the size of polar nanoregions and freezing temperature. Moreover, the results shown that both the volume fraction of polar nanoregions and remnant polarization may decrease by doping La³⁺ or Na⁺. This indicates that Pb²⁺ ions are critical for the polarization of Pb(Mg_1/3Nb_2/3)O₃, therefore, the substitution of Pb²⁺ by La³⁺ or Na⁺ ions reduces its remnant polarization. This work may provide some insights for understanding the structure-property relationship for relaxor ferroelectrics.