Effect of different MnO₂ phases (β-, γ-, and ε-) on the microstructure and piezoelectric properties of Pb(Zr_1/2Ti_1/2)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃ ceramics for energy harvesting

This study reports 0.83Pb(Zr_1/2Ti_1/2)O₃–0.11Pb(Zn_1/3Nb_2/3)O₃–0.06Pb(Ni_1/3Nb_2/3)O₃ (PZNNT) ceramics doped with MnO₂ were obtained through the conventional solid-state reaction method. The effects of MnO₂ additive with different phases (β-, γ-, and ε-) on the microstructure and piezoelectric properties of PZNNT ceramics were discussed under the same condition. On the basis of X-ray photoelectron spectroscopy (XPS), the results clearly showed that Mn ions in different crystal forms of MnO₂ could convert from Mn⁴⁺ ions to diverse valence states (Mn²⁺, Mn³⁺) and produce different oxygen vacancies. Furthermore, the relevant electric properties of samples increased as follows: PZNNT/β-MnO₂ < PZNNT/ε-MnO₂ < PZNNT/γ-MnO₂. The optimal electric properties could be obtained by adding 1.5 mol% γ-MnO₂, the energy conversion factor (d₃₃ × g₃₃), the mechanical quality factor (Q_m), the electromechanical coupling factor (k_p), and the Curie temperature (T_c) which were 9859 × 10⁻¹⁵ m²/N, 357, 0.556, and 315 °C, respectively. It indicates that γ-MnO₂-modified PZNNT ceramics are potential candidate materials for piezoelectric energy harvesting.