Structure and piezoelectric properties of new (Bi_0.5Na_0.5)_1-x-yBa_x(Yb_0.5Na_0.5)_yTiO₃lead-free ceramics

New lead-free ceramics (Bi0.5Na0.5)1-x-yBax(Yb0.5Na0.5)yTiO3(x = 0.02-0.10 and y = 0-0.04) have been prepared by an ordinary sintering technique and their structure and piezoelectric properties have been studied. X-ray diffraction shows that Ba2+and Yb3+diffuse into the Bi0.5Na0.5TiO3lattices to form a solid solution with a pure perovskite structure and a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases is formed at 0.04 < x < 0.10. The partial substitutions of Ba2+and Yb3+for A-site ions of Bi0.5Na0.5TiO3decrease effectively the coercive field Ecand improve significantly the remanent polarization Pr. The ceramics with x = 0.06 and y = 0-0.02 situate within the MPB and possess the lower Ecand larger Pr, and thus exhibit optimum piezoelectric properties: d33= 155-171 pC/N and kp= 29.2-36.7%. The temperature dependences of the dielectric and ferroelectric properties suggest that the ceramics may contain both the polar and non-polar regions at temperatures near/above Td.