Effects of substitutions of Nd³⁺ for Sr²⁺ on the properties of SrBi₂Nb₂O₉ ceramics and their mechanism

(Sr_1-3x/2A_x/2Nd_x) Bi₂Nb₂O₉ (x=0, 0.05, 0.1 and 0.2) ceramics are prepared by traditional solid-reaction method, and effects of substitutions of Nd³⁺ for Sr²⁺ on the properties of SrBi₂Nb₂O₉ ceramics and their mechanism are investigated. The results show that the temperature spectra of dielectric constant and loss for these Nd-doped samples are obviously characteristic of ion relaxor polarization. The partial substitution of Nd³⁺ for Sr²⁺ leads to the slight reduction in remanent polarization (P_r) and the increase in piezoelectric coefficient d₃₃, which can be attributed to the increase in dielectric constant of samples according to ferroelectric thermodynamics theory. Raman spectrum shows that no change in the Curie temperature (T_C) of (Sr_1-3x/2A_x/2Nd_x) Bi₂Nb₂O₉ samples is observed, which might result from no appreciable variation in NbO₆ octahedron distortion. For (Sr_1-3x/2A_x/2Nd_x) Bi₂Nb₂O₉ ceramics, the substitution of Nd³⁺ for Sr²⁺ increases permittivity ε_r, piezoelectric coefficient d₃₃, and electromechanical coupling coefficient K_p and reduces mechanical quality factor Q_m, but it does not change temperature coefficient of harmonic frequency value.