Influence of CuO on the structure and piezoelectric properties of the alkaline niobate-based lead-free ceramics

Recently, it was reported that the alkaline niobate-based (K,Na,Li)(Nb,Ta,Sb)O-3 (LF4) perovskite ceramics showed excellent piezoelectric properties and have been regarded as a new candidate of lead-free piezoelectric materials. However, the effects of additives on the piezoelectric property of LF4 have not been studied intensively so far. In this study, the effect of CuO addition to the LF4 was investigated. The sample showed a tetragonal phase at room temperature and also a second phase with low melt point. With 0.05 wt% CuO added, the Cu2+ firstly incorporated into the A site, while higher amounts of Cu2+ substituted B-site ions. The CuO-doping changed the LF4 to hard piezoelectric ceramics with improvement of mechanical quality factor from 26 to 137 but the piezoelectric d(31) constant and the electromechanical coupling constant reduced drastically at the same time.