Effect of MnO2 doping on the structure and electrical properties of Sr1.95Ca0.05NaNb5O15 lead free piezoelectric ceramics

Piezoelectric ceramics Sr1.95Ca0.05NaNb5O15+y wt%MnO2(SCNNM) with y ranging from 0 to 1.5 were prepared by solid-state reaction method. The results indicated that the calcined SCNNM ceramics retain a single phase of tetragonal tungsten-bronze structure with y&le0.7. When y≥1.0, a secondary phase was observed. The addition of a little MnO2 could decrease the sintering temperature, promote grain growth. The dielectric, piezoelectric and ferroelectric properties of the SCNNM ceramics significantly increased. At room temperature, the SCNNM ceramic with y=0.5 exhibits the optimum properties: piezoelectric coefficient d33=190 pC/N, mechanical quality factor Qm=1455, planer and thickness electromechanical coupling factors Kp=13.4% and Kt=36.5%, dielectric constant Εr=2123, loss tangent tanδ=0.038, remanent polarization Pr=4.76 μC/cm2, coercive field Ec=12.68 kV/cm, and curie temperature Tc=260 oC.