Evolving Differentiated Local Polar Displacement and Relaxor Behavior in Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃Perovskites

Lead-based relaxor ferroelectrics feature exceptional dielectric and electromechanical properties. The inherent local structural inhomogeneity remains poorly characterized and impedes the understanding of their unique electrical behavior. Herein, the local structure of a technologically important 0.75Pb(Mg_1/3Nb_2/3)O₃-0.25PbTiO₃relaxor is studied as a function of temperature, by employing neutron total scattering combined with newly advanced reverse Monte Carlo modeling. The statistical analysis of local cationic polar displacement vectors demonstrates that a prevailing order/disorder feature and strong displacive behavior are observed in Pb and Ti, but both weak components are observed in Nb/Mg. This leads to trifurcated polar behavior across the feature temperatures. Importantly, these distinct cationic polar vectors are correlated and present a microscopic picture, where sporadic correlated orthorhombic polar clusters are embedded in a long-range rhombohedral polar matrix at low temperature. Their fraction extends with increasing temperature, presenting strong ferroelectricity with dielectric relaxation macroscopically. Furthermore, the long-range rhombohedral polar ordering is disrupted by temperature, forming free-oriented polar clusters with reducing electric dipole length, gradually losing their macroscopic polarization, and resulting in a diffuse phase transition behavior. Altogether, this offers a fundamental basis in terms of local polar fluctuations in inferring the nature of the unique properties of relaxor ferroelectrics.