Structure, ferroelectric and piezoelectric properties of (Bi_0.98-xLa_0.02Na_1-x)_0.5Ba_xTiO₃lead-free ceramics

Lead-free (Bi0.98-xLa0.02Na1-x)0.5BaxTiO3ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction∈show∈that∈La2+∈and∈Ba2+diffuse∈into∈the∈Bi0.5Na0.5TiO3lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi0.5Na0.5TiO3ceramics, the (Bi0.98-xLa0.02Na1-x)0.5BaxTiO3ceramics possess much smaller coercive field Ecand larger remanent polarization Pr. Because of the low Ec(3.38 kV/mm), large Pr(46.2 μC/cm2) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d33=181 pC/N and kp=36.3%. The depolarization temperature Tdreaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above Td.