Piezoelectric and ferroelectric properties of (Bi_0.94-xLa_xNa_0.94)_0.5Ba_0.06TiO₃lead-free ceramics

Lead-free piezoelectric ceramics (Bi0.94-xLaxNa0.94)0.5Ba0.06TiO3have been fabricated by an ordinary sintering technique, and their piezoelectric and ferroelectric properties have been studied. The results of x-ray diffraction reveal that La3+and Ba2+diffuse into the Bi0.5Na0.5TiO3lattices to form a new solid solution with a pure perovskite structure. After the partial substitution of La3+for Bi3+in the (Bi0.94-xLaxNa0.94)0.5Ba0.06TiO3ceramics (x = 0-0.04), the ceramics exhibit a lower coercive field Ecand a larger remanent polarization Pr. Because of the large Prand low Ec, the ceramics with x = 0.02-0.04 exhibit optimum piezoelectric properties: d33= 181-196 pC N-1and kP= 33.2-36.3%. The depolarization temperature Tddecreases with increasing x (x = 0 - 0.04). At the high La3+level (x = 0.06-0.12), the ceramics exhibit weak ferroelectricity and thus possess very poor piezoelectricity, and the low dielectric anomaly at Tddisappears. 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 Td, while for the ceramics with x = 0.06-12, the polar and non-polar regions coexist at room temperature.