Effects of Oxide Additives on the Phase Structures and Electrical Properties of SrBi₄Ti₄O₁₅ High-Temperature...

In this work, SrBi₄Ti₄O₁₅ (SBT) high-temperature piezoelectric ceramics with the addition of different oxides (Gd₂O₃, CeO₂, MnO₂ and Cr₂O₃) were fabricated by a conventional solid-state reaction route. The effects of oxide additives on the phase structures and electrical properties of the SBT ceramics were investigated. Firstly, X-ray diffraction analysis revealed that all these oxides-modified SBT ceramics prepared presented a single SrBi₄Ti₄O₁₅ phase with orthorhombic symmetry and space group of Bb21m, the change in cell parameters indicated that these oxide additives had diffused into the crystalline lattice of SBT and formed solid solutions with it. The SBT ceramics with the addition of MnO₂ achieved a high relative density of up to 97%. The temperature dependence of dielectric constant showed that the addition of Gd₂O₃ could increase the T_C of SBT. At a low frequency of 100 Hz, those dielectric loss peaks appearing around 500 °C were attributed to the space-charge relaxation as an extrinsic dielectric response. The synergetic doping of CeO₂ and Cr₂O₃ could reduce the space-charge-induced dielectric relaxation of SBT. The piezoelectricity measurement and electro-mechanical resonance analysis found that Cr₂O₃ can significantly enhance both d₃₃ and k_p of SBT, and produce a higher phase-angle maximum at resonance. Such an enhanced piezoelectricity was attributed to the further increased orthorhombic distortion after Ti⁴⁺ at B-site was substituted by Cr³⁺. Among these compositions, Sr_0.92Gd_0.053Bi₄Ti₄O₁₅ + 0.2 wt% Cr₂O₃ (SGBT-Cr) presented the best electrical properties including T_C = 555 °C, tan δ = 0.4%, k_p = 6.35% and d₃₃ = 28 pC/N, as well as a good thermally-stable piezoelectricity that the value of d₃₃ was decreased by only 3.6% after being annealed at 500 °C for 4 h. Such advantages provided this material with potential applications in the high-stability piezoelectric sensors operated below 500 °C.