Processing, phase evolution and electrical properties of “lead free” KNN–BF–CuO eco-piezoceramic from mechanochemically activated precursors

“Lead free” piezoceramics 0.99K0.5Na0.5NbO3-0.01BiFeO3 (KNN–BF) with increasing amount of CuO (0, 0.5, 1 wt.%) were prepared through a scalable combination of High Energy Ball Milling, calcination at 900 °C and air sintering. The effect of CuO on the sintering behaviour and electrical properties of KNN–BF was investigated. The compositions examined show high-density values (>95% of TD) at their optimized sintering temperatures. Small addition of CuO (0.5 wt.%) causes an increase in the size of grains, however an excess of CuO (1 wt.%) inhibits the growth of grains due to the excess of liquid phase. The KNN–BF composition shows promising electrical properties (d33 = 150 pC/N; kp = 42%; Qm = 150) which are mainly related to the high density achieved and to the orthorhombic-tetragonal symmetry coexistence. The addition of 0.5 wt.% of CuO causes an increase in the quality factors (Qm = 235; Q(d31) = 207).