Valence-state-dependent defect engineering in Mn-doped PbTiO3 ceramics: Enhancing electromechanical properties through tetragonal distortion and defect dipoles

Mn exerts multiple effects on lead-based piezoelectric ceramics due to its multivalent nature and strong affinity for oxygen vacancies; however, the mechanisms associated with distinct valence states are not yet fully understood. In this work, experimental characterization combined with first-principles calculations was employed to elucidate the valence-state-resolved structure–property relationships in PbTiO3−xMn (x = 0.01–0.04) ceramics. Mn2+/Mn3+ ions formed defect polarons and dipoles, which enhanced tetragonal distortion and suppressed domain-wall motion. Consequently, the mechanical quality factor (Qm) reached 1050 at x = 0.02. In contrast, Mn4+ incorporation reduced tetragonality due to c axis lattice contraction. Raman spectra and EPR analyses indicate that Mn3+-dominated defect dipoles were responsible for the largest distortion (c/a = 1.0575) and the highest Qm. Furthermore, the Mn′Ti polaron is structurally unstable due to Jahn–Teller distortion and is stabilized only through (Mn′Ti−Vo∙∙)∙ defect-dipole formation. These findings establish a clear structure–property relationship, demonstrate the critical role of valence-specific defect engineering in tailoring the macroscopic electrical properties of Mn-doped PbTiO3 ceramics, and offer guidance for the design and optimization of other lead-based piezoelectric ceramics.