Effects of MnO2 and sintering temperature on microstructure, ferroelectric, and piezoelectric properties of Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics

Ba0.85Ca0.15Ti0.90Zr0.10O3 + xmol% MnO2 lead-free ceramics have been prepared by a conventional sintering method and the effects of MnO2 and sintering temperature on microstructure, ferroelectric, and piezoelectric properties of Ba0.85Ca0.15Ti0.90Zr0.10O3 lead-free ceramics have been studied. The addition of 0.25 mol% MnO2 promotes grain growth, improves the ferroelectricity of the ceramics and strengthens ferroelectric tetragonal–ferroelectric orthorhombic phase transition near 40 °C. Because of the coexistence of tetragonal and orthorhombic phases and the combinatory effects of soft and hard doping of Mn ions, the ceramic with x = 0.25 exhibits the optimum piezoelectric properties (d 33 = 306 pC/N and k p = 42.2 %, respectively). Excess MnO2 inhibits the grain growth and degrades the ferroelectric and piezoelectric properties of the ceramics. Sintering temperature has an important influence on the microstructure, tetragonal–orthorhombic phase transition near 40 °C, ferroelectric and piezoelectric properties of the ceramics. The increase in sintering temperature leads to large grains and more noticeable tetragonal–orthorhombic phase transition near 40 °C, enhances ferroelectricity and thus improves effectively the piezoelectricity of the ceramics. The Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramic sintered at 1350 °C possesses the optimum piezoelectric constant d 33 value of 373 pC/N.