Effects of MnO₂ addition on microstructure and electrical properties of (Bi_0.5Na_0.5) _0.94Ba_0.06TiO₃ ceramics

In this letter, MnO₂-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT-6) lead-free piezoelectric ceramics were synthesized by solid state reaction, and the microstructure and electrical properties of the ceramics were investigated. X-ray diffraction (XRD) reveals that all specimens take on single perovskite type structure, and the diffraction peaks shift to a large angle as the MnO₂ addition increases. Scanning electron microscopy shows that the grain sizes increases, and then decreases with increasing the MnO₂ content. The experiment results indicate that the electrical properties of ceramics are significantly influenced by the MnO₂ content, and the ceramics with homogeneous microstructure and excellent electrical properties are obtained with addition of 0.3 wt% MnO₂ and sintered at 1160°C. The piezoelectric constant (d₃₃), the electromechanical coupling factor (k _p ), the dissipation factor (tan δ) and the dielectric constant (ɛ _r ) reach 160 pC/N, 0.29, 0.026 and 879, respectively. These excellent properties indicate that the MnO₂-doped BNBT-6 ceramics can be used for actuators.