Electrical and structural properties of iron-doped β-alumina

β-alumina containing 50 w/o Fe exhibits high electronic conductivity when sintered in air but Mössbauer studies have shown the presence of Fe₃O₄. Single-phase β-alumina containing 50 w/o Fe could be prepared by sintering at 1400°C for 4–4.5 h followed by annealing at 1300°C for 96 h encapsulated with coarse β-alumina powder enriched with Na₂CO₃. Mössbauer spectroscopy indicated that all iron was present as Fe(III). Complex-plane impedance data showed a maximum bulk $\text{σ}{}_{\mathrm{25°C}}\text{= 5.56 × 10}{}^{-4}\text{(Ω cm)}{}^{-1}$ with little electronic conductivity. Reduction treatments on Fe-doped β-alumina utilizing H₂:N₂ gas were successful in producing a mixed conductor containing Fe(II) and Fe(III) but also produced a distorted β-alumina lattice. This material exhibited an electronic conductivity $\text{σ}{}_{\mathrm{e,25°C}}\text{= 2 × 10}{}^{-4}\text{(Ω cm)}{}^{-1}$ and a bulk ionic conductivity $\text{σ}{}_{\mathrm{b,25°C}}\text{= 1.35 × 10}{}^{-4}\text{(Ω cm)}{}^{-1}$.