Effects of MnO2 on the microstructure and electrical properties of 0.94(K0.5Na0.5)NbO3–0.06Ba(Zr0.05Ti0.95)O3 lead-free ceramics

Lead-free ceramics MnO2-doped 0.94(K0.5Na0.5)NbO3–0.06Ba(Zr0.05Ti0.95)O3 have been fabricated by an ordinary sintering technique and the effects of MnO2 on the microstructure and electrical properties of the ceramics have been studied. Our results reveal that a small amount of MnO2 (0.50–1.00 mol%) can improve effectively the densification and electrical insulation of the ceramics. For 1 mol% MnO2-doped 0.94(K0.5Na0.5)NbO3–0.06Ba(Zr0.05Ti0.95)O3 ceramics, the ferroelectric tetragonal-ferroelectric orthorhombic phase transition (TO–T) resides near room temperature, indicating the coexistence of the orthorhombic and tetragonal phases at room temperature. Because of high densification, good electrical insulation, the donor- and acceptor-doping effects of MnO2, and the coexistence of the orthorhombic and tetragonal phases, the piezoelectric and dielectric properties of the ceramics are improved considerably. The 0.94(K0.5Na0.5)NbO3–0.06Ba(Zr0.05Ti0.95)O3 ceramics with 1.00 mol% MnO2 doping possess optimum properties: d33 = 234 pC/N, kp = 49%, kt = 48%, ɛr = 1191, tan δ = 1.20% and Tc = 318 °C.