Magnocolumbites Mg<sub>1–<i>x</i></sub><i>M<sub>x</sub></i>Nb<sub>2</sub>O<sub>6−δ</sub> (<i>x</i> = 0, 0.1, and 0.2; <i>M</i> = Li and Cu) as New Oxygen Ion Conductors: Theoretical Assessment and Experiment
Yelizaveta A. Morkhova, М. С. Королева, Anastasia V. Egorova, А. А. Пименов, Aleksei G. Krasnov, Б. А. Макеев, Vladislav A. Blatov, Artem A. Kabanov
Abstract
MgNb2O6 with a columbite structure was theoretically predicted as a prospective oxygen ion conductor. This compound was successfully synthesized by the Pechini method. The Li- and Cu-doped samples Mg1–xMxNb2O6−δ (x = 0.1 and 0.2; M = Li and Cu) were prepared in the same way. The columbite structure (Sp.gr. Pbcn) was formed for the samples with x = 0 and x(Cu) = 0.1 and 0.2, while Li-doping led to the formation of two-phase ceramics with Mg1–xLixNb2O6−δ and LiNbO3 components. The lithium and copper doping led to a decreasing sintering temperature by 100–200 °C down to ∼1050 °C. For Mg1–xLixNb2O6−δ (x = 0, 0.1, and 0.2), the experiments revealed pure oxygen ion conductivity of σ ∼10–5 Scm–1 at 800 °C, an activation energy Ea,σ of 0.86 eV, and good stability in a wide range of temperature, oxygen partial pressure, and in an atmosphere of carbon dioxide. For the Cu-doped samples, mixed n-type electronic and oxygen ion (T > 400 °C) conductivity was determined up to 2 × 10–3 Scm–1 at 800 °C with Ea,σ = 0.21 eV at x(Cu) = 0.2.