Effect of MnO₂ addition on the structure and electrical properties of Pb(Zn_1/3Nb_2/3 )_0.20(Zr_0.50Ti_0.50 )_0.80O₃ ceramics

Pb(Zn_1/3Nb_{2/3 0.20}(Zr_0.50Ti_{0.50 0.80}O₃ ceramics of pure perovskite structure were prepared by the two-stage method with the addition of 0-3.0 wt% MnO₂ and their piezoelectric properties were investigated systematically. The MnO₂ addition influences in a pronounced way both the crystal structure and the microstructure of the materials. The materials are transformed from the tetragonal to the rhombohedral structure, and the grain size is enhanced when manganese cations are added. The distortion of crystal structure for samples with MnO₂ addition can be explained by the Jahn-Teller effect. The values of electromechanical coupling factor (k_p) and dielectric loss (tan δ) are optimized for 0.5-wt%-MnO₂-doped samples (k_p = 0.60, tan δ = 0.2%) and the mechanical quality factor (Q_m) is maximized for 1.0-wt%-MnO₂-doped samples (Q_m = 1041), which suggests that oxygen vacancies formed by substituting Mn³⁺ and Mn²⁺ ions for B-site ions (e.g., Ti⁴⁺ and Zr⁴⁺ ions) in the perovskite structure partially inhibited polarization reversal in the ferroelectrics. The ceramics with 0.50-1.0 wt% MnO₂ addition show great promise as practical materials for piezoelectric applications.