Effect of grain size on crystal structure and electric properties of Bi(Ni2/3Ta1/3)O3-PbTiO3 ferroelectric ceramics

The effect of grain size on crystal structure and the ferroelectric, dielectric, and piezoelectric properties of 0.38Bi(Ni2/3Ta1/3)O3-0.62PbTiO3 ceramics was studied herein. By controlling the sintering time, 0.38Bi(Ni2/3Ta1/3)O3-0.62PbTiO3 ceramics with different grain sizes were prepared by the conventional solid-state reaction. It was found that the crystal structure of the ceramics changed slightly with the increase of grain size, from a pure tetragonal perovskite structure to a combination of tetragonal and rhombohedral phases. Both the Curie temperature TC and the depolarization temperature Td of the ceramics decreased with increasing grain size. However, the degree of dielectric relaxation first increased and then decreased, with the relaxation factor γ ranging from 1.35 to 1.87. The remnant polarization Pr and coercive field EC also first increased and then decreased, whereas the strain increased with the increase of grain size. The high field strain coefficient d*33 and piezoelectric coefficient d33 both increased with the increase of grain size. However, in this ceramic system, the electromechanical coupling coefficient kp and mechanical quality factor Qm changed independently of the variation in grain size.