Study on Poling Mechanism and Electromechanical Property of Lead-Free Piezoelectric Materials

When mechanical stress is applied to a non-centrosymmetric crystal, charge displacement induces polarization (direct piezoelectric effect), whereas an applied electric field produces strain (converse piezoelectric effect). Piezoelectric materials have become indispensable in modern devices since their discovery in 1880–1881. Although lead-based materials such as PZT exhibit excellent performance, environmental and health concerns have driven the development of lead-free alternatives. Despite extensive compositional exploration over the past two decades, no lead-free material has yet fully replaced lead-based counterparts, and challenges related to reliability and cost remain. This dissertation focuses on poling treatment, a post-synthesis process that aligns ferroelectric domains, rather than on further compositional modification. Three poling methods—DC poling, AC poling, and unipolar (Uni) poling—were applied to three lead-free model ceramics: Ba(Zr0.1Ti0.9)O3, 0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Zr0.2Ti0.8)O3, and (Na0.55K0.45)NbO3. Their domain structures and piezoelectric properties were systematically compared. These results clarify the relationships among crystal symmetry, microstructure, domain configuration, and piezoelectric performance, providing insight into poling mechanisms in lead-free piezoelectric ceramics and contributing to their future development.