Effects of MnO2 on phase structure, microstructure and electrical properties of (K0.5Na0.5)0.94Li0.06NbO3 lead-free ceramics

The effects of a small amount MnO2 (0-1.20 mol%) doping on the phase transition behavior, microstructure and electrical properties of (K0.5Na0.5)0.94Li0.06NbO3 (KNLN6) ceramics have been investigated. X-ray diffraction analysis showed that the ceramics underwent a perovskite structure transition from tetragonal to orthorhombic symmetry with increasing the MnO2 content, which is similar to the morphtropic phase boundary (MPB). SEM and density studies revealed that a small amount of MnO2 improved effectively the densification of the KNLN6 ceramics. Because of the high densification, the mechanical quality factor Qm of the KNLN6 ceramics were significantly enhanced by MnO2 addition which meant MnO2-doping changed the KNLN6 to “hard” ceramics. For 1.20 mol% MnO2-doped KNLN6 ceramics, the mechanical quality factor Qm reached up to 301, which increased by four times as compared with KNLN6. The piezoelectric constant d33 and the planar electromechanical coefficient kp still maintained relatively high levels, which were about 141 pC/N and 32.0%, respectively.