Structure, ferroelectric and piezoelectric properties of (Bi_(0.98-x)La_(0.02)Na_(1-x))_(0.5)Ba_xTiO_3 lead-free ceramics

摘要

Lead-free (Bi_(0.98-x)La_(0.02)Na_(1-x))_(0.5)Ba_xTiO_3 ceramics 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 La~(2+) 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, and a morphotropic phase boundary (MPB) exists at 0.04 < x < 0.10. Compared with pure Bi_(0.5)Na_(0.5)TiO_3 ceramics, the (Bi_(0.98-x)La_(0.02)Na_(1-x))_(0.5)Ba_xTiO_3 ceramics possess much smaller coercive field E_c and larger rema-nent polarization P_r. Because of the low Ec (3.38 kV/mm), large P_r (46.2 μC/cm~2) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x = 0.06: d_(33) = 181 pC/N and k_p = 36.3%. The depolarization temperature T_d reaches 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 T_d.