Effect of MnO2 Addition on the Electrical Properties of PNZST Ceramics

Abstract

(Pb0.99Nb0.02)[(Zr0.70Sn0.30)xTi1−x]0.98O3 (PNZST) piezoelectric ceramics of pure perovskite structure were prepared by a conventional ceramic fabrication method, where x = 0.48–0.56. When x = 0.52, the ceramics exhibit a high piezoelectric coefficient (d33 ∼ 490), but the mechanical quality factor (Qm) is only 72. To increase the Qm and not dramatically lower the d33, MnO2 was chosen as the additive. The effects of adding MnO2 on the sinterability, structure, and electrical properties of PNZST ceramics were investigated in detail. With a small addition of MnO2 (≤0.6 wt.%), the Mn ions are homogeneously dissolved in the PNZST ceramic, leading to full densification when sintered at 1,300 °C. However, further addition of MnO2 prevents densification, causing a high porosity and small grain size. The doping of MnO2 transforms the phase structure from tetragonal to rhombohedral. The addition of MnO2 up to a maximum of 0.6 wt.% remarkably improves the mechanical quality factor (Qm) of PNZST ceramics, simultaneously as well as maintaining a high d33 and kp. PNZST with 0.6 wt.% MnO2 exhibits excellent electrical properties with piezoelectric coefficient d33 = 392 pC/N, electromechanical coupling factor kp = 0.60, mechanical quality factor Qm = 1,050, dielectric constant er = 1,232, dielectric dissipation tanδ = 0.0058, and Curie temperature TC = 300 °C.