Contrasting Piezoelectric Mechanisms of Transition Metal Dopants in Complex Lead-Based Perovskite: The Decisive Role of Ionic Site Selectivity

Over the past years, defect engineering strategies, particularly heterovalent doping, have served as a key approach for tailoring the electromechanical properties of ferroelectrics. However, some microscopic mechanisms, such as the discrepant piezoelectricity regulation behavior induced by transition metal dopants in complex lead-based perovskite systems, remain poorly understood. In this study, we systematically investigated the respective effects of Mn and Fe on the piezoelectric performance of PNN-PZT-PMW ceramics. Our results reveal that Fe doping does not enhance the mechanical quality factor (Qm) and only slightly reduces the piezoelectric constant (d33). In contrast, Mn doping significantly improves Qm but markedly decreases d33. By combining ferroelectric scaling behavior analysis with hierarchical structural characterization, we attribute the negligible variation in electrical performance upon Fe doping primarily to the promotion of long-range ferroelectric order and the competitive interaction between two distinct types of defect dipoles FeNb″-VO•• and FeNi•-VPb″. Conversely, Mn doping induces a pronounced hardening effect due to the formation of defect dipoles such as MnZr/Ti″-VO•• or MnNb″-VO••. These dipoles effectively pin domain-wall motion, leading to a stronger dielectric relaxation effect and necessitating a substantially higher electric field to activate the intrinsic piezoelectric response. This study elucidates the decisive role of ionic site selectivity in governing defect dipole formation and polarization dynamics, providing an important theoretical framework for the precise design of high-performance piezoelectric materials through defect engineering.