Mechanistic Decoupling of Giant Electrostrain and Piezoelectric Coefficients at the Morphotropic Phase Boundary in PMN-30PT Single Crystals

The morphotropic phase boundary (MPB) with multiphase coexistence serves as a critical region for piezoelectric materials, but the individual contributions of various microscopic mechanisms to the overall electromechanical response remains a challenge for further subdivision. Here, we systematically investigate the microscopic origins of outstanding piezoelectricity in <001>-oriented Pb(Mg1/3Nb2/3)O3-30PbTiO3 (PMN-30PT) single crystals and quantitatively identify the dominant factors for giant electrostrain and ultrahigh piezoelectric coefficient. Large electrostrain arises predominantly from polarization rotation within the easily distorted monoclinic phase and the high-energy-barrier monoclinic-to-tetragonal phase transition, enabled by a synergistic interplay of broad electric field adaptability and high strain sensitivity. In contrast, the peak piezoelectric coefficient (d33 > 2100 pC/N) is attributed to the low-energy-barrier rhombohedral-to-monoclinic phase transition, which facilitates polarization rotation. Furthermore, the critical yet distinct roles of monoclinic phase compared to piezoelectric and electrostrain have been confirmed. By the quantitative segmentation of various microscopic factors, this work provides fundamental insights into the design of high-performance piezoelectrics.