Piezoelectric and ferroelectric properties of (Bi0.94−xLaxNa0.94)0.5Ba0.06TiO3lead-free ceramics

Lead-free piezoelectric ceramics (Bi 0.94− x La x Na 0.94 ) 0.5 Ba 0.06 TiO 3 have been fabricated by an ordinary sintering technique, and their piezoelectric and ferroelectric properties have been studied. The results of x-ray diffraction reveal that La 3+ and Ba 2+ diffuse into the Bi 0.5 Na 0.5 TiO 3 lattices to form a new solid solution with a pure perovskite structure. After the partial substitution of La 3+ for Bi 3+ in the (Bi 0.94− x La x Na 0.94 ) 0.5 Ba 0.06 TiO 3 ceramics ( x = 0–0.04), the ceramics exhibit a lower coercive field E c and a larger remanent polarization P r . Because of the large P r and low E c , the ceramics with x = 0.02–0.04 exhibit optimum piezoelectric properties: d 33 = 181–196 pC N −1 and k P = 33.2–36.3%. The depolarization temperature T d decreases with increasing x ( x = 0 − 0.04). At the high La 3+ level ( x = 0.06–0.12), the ceramics exhibit weak ferroelectricity and thus possess very poor piezoelectricity, and the low dielectric anomaly at T d disappears. In addition, the ceramics exhibit a relaxor characteristic, which probably results from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics with x = 0–0.04 may contain both polar and non-polar regions at temperatures above T d , while for the ceramics with x = 0.06–12, the polar and non-polar regions coexist at room temperature.