The Contributions of Polar Nanoregions to the Dielectric and Piezoelectric Responses in Domain-Engineered Relaxor-PbTiO₃ Crystals

The existence of polar nanoregions is the most important characteristic of relaxor-based ferroelectric materials. Recently, the contributions of polar nanoregions to the shear piezoelectric property of relaxor-PbTiO₃ (PT) crystals are confirmed in a single domain state, accounting for 50%–80% of room temperature values. For electromechanical applications, however, the outstanding longitudinal piezoelectricity in domain-engineered relaxor-PT crystals is of the most significance. In this paper, the contributions of polar nanoregions to the longitudinal properties in [001]-poled Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ and [110]-poled Pb(Zn_1/3Nb_2/3)O₃-0.15PbTiO₃ (PZN-0.15PT) domain-engineered crystals are studied. Taking the [110]-poled tetragonal PZN-0.15PT crystal as an example, phase-field simulations of the domain structures and the longitudinal dielectric/piezoelectric responses are performed. According to the experimental results and phase-field simulations, the contributions of polar nanoregions (PNRs) to the longitudinal properties of relaxor-PT crystals are successfully explained on the mesoscale, where the PNRs behave as “seeds” to facilitate macroscopic polarization rotation and enhance electric-field-induced strain. The results reveal the importance of local structures to the macroscopic properties, where a modest structural variation on the nanoscale greatly impacts the macroscopic properties.