Effect of grain size on crystal structure and electric properties of Bi(Ni_2/3Ta_1/3)O₃-PbTiO₃ ferroelectric ceramics

The effect of grain size on crystal structure and the ferroelectric, dielectric, and piezoelectric properties of 0.38Bi(Ni_2/3Ta_1/3)O₃-0.62PbTiO₃ ceramics was studied herein. By controlling the sintering time, 0.38Bi(Ni_2/3Ta_1/3)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 T_C and the depolarization temperature T_d 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 P_r and coercive field E_C 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 k_p and mechanical quality factor Q_m changed independently of the variation in grain size.