Fig. 1: Schematic illustrations of conventional O-T PBE and our local Cu-acceptor defect dipoles embedded O-T PBE strategy.

a For the conventional O-T PBE strategy, only d33 can be enhanced due to the easy polarization rotation and domain switching, leaving an unbalanced development of d33 and Qm. b For our local Cu-acceptor defect dipoles embedded O-T PBE strategy, both d33 and Qm can be simultaneously improved because of the coupling effect of local Cu-acceptor defect dipoles and O-T PBE. Note that PBE is the abbreviation of phase boundary engineering.