Microstructure, ferroelectric and piezoelectric properties of MnO2-modified Ba0.70Ca0.30TiO3 lead-free ceramics

Abstract

Lead-free Ba0.70Ca0.30TiO3 + x mol% MnO2 (abbreviated as BCTMx, x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0 and 1.2) piezoelectric ceramics were synthesized by the solid-state reaction method. The effects of MnO2 additives on the phase transition, microstructure, dielectric, ferroelectric, strain behaviors and piezoelectric properties are investigated. BCTMx ceramics (x = 0–1.2) exhibit diphasic tetragonal and orthorhombic phases. The tetragonal phase is gradually suppressed by increasing x. As x increases from 0 to 1.2, the Curie temperature (TC) decreases monotonically from 128 to 45 °C, while the grain size, dielectric and ferroelectric properties increase and reach the maximum near x = 0.6. On the other hand, the piezoelectric coefficient (d33) and the electromechanical coupling coefficient (kp%) decrease simultaneously, whereas the mechanical quality factor (Qm), bipolar and unipolar strain increase and reach the maximum values of 684, 0.28% and 0.24%, respectively, near x = 0.6. The optimum electrical performance with $$\varepsilon_{r}$$ = 1323, tan $$\delta$$ = 0.08, TC = 66 °C, Pmax = 12.2 μC/cm2, Pr = 6.9 μC/cm2, EC = 13.3 kV/cm, d33 = 116 pC/N, kp% = 0.22%, Qm = 684 and the normalized strain $$d_{33}^{*}$$ = Smax/Emax as high as 480 pm/V were observed for x = 0.6. The high strain and Qm suggested that the MnO2-modified Ba0.70Ca0.30TiO3 ceramics are promising candidate for high power applications.