Dielectric and piezoelectric properties of Cu2+-doped alkali Niobates

The effect of Cu2+ addition (0.5–2 mol%) on microstructure and electromechanical properties of lead-free piezoelectric system of (K0.44Na0.52Li0.04)(Ta0.1Sb0.06Nb0.84)O3 (KNN-LT-LS) was investigated through two processing methods; namely perovskite and mixed-oxide. The addition of Cu2+ showed an increase in grain size and relative density of the undoped ceramics in both processing techniques. Introduction of Cu2+ stabilized the orthorhombic phase at room temperature by shifting the tetragonal–orthorhomic phase transition to higher temperatures while did not show any major changes in Tc. The polarization-field response of Cu2+-doped ceramics showed a decline in both remnant polarization and coercive field, thus reducing the area of the hysteresis loop. This shrinkage in hysteresis loop was manifested through a large improvement in mechanical quality factor, nearly 4 times that of undoped ceramic. Within the studied range of Cu2+ addition, the ceramic with 0.5 mol% of Cu2+ prepared by mixed-oxide route represented a relatively desirable balance between the degradation of the electromechanical properties, improvement in temperature stability, and mechanical quality factor.