Effects of Oxide Additives on the Phase Structures and Electrical Properties of SrBi(4)Ti(4)O(15) High-Temperature Piezoelectric Ceramics

In this work, SrBi(4)Ti(4)O(15) (SBT) high-temperature piezoelectric ceramics with the addition of different oxides (Gd(2)O(3), CeO(2), MnO(2) and Cr(2)O(3)) 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 SrBi(4)Ti(4)O(15) 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 MnO(2) achieved a high relative density of up to 97%. The temperature dependence of dielectric constant showed that the addition of Gd(2)O(3) 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 CeO(2) and Cr(2)O(3) could reduce the space-charge-induced dielectric relaxation of SBT. The piezoelectricity measurement and electro-mechanical resonance analysis found that Cr(2)O(3) can significantly enhance both d(33) 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 Ti(4+) at B-site was substituted by Cr(3+). Among these compositions, Sr(0.92)Gd(0.053)Bi(4)Ti(4)O(15) + 0.2 wt% Cr(2)O(3) (SGBT-Cr) presented the best electrical properties including T(C) = 555 °C, tan δ = 0.4%, k(p) = 6.35% and d(33) = 28 pC/N, as well as a good thermally-stable piezoelectricity that the value of d(33) 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.