Magnocolumbites Mg_1–<i>x</i><i>M_x</i>Nb₂O_6−δ (<i>x</i> = 0, 0.1, and 0.2; <i>M</i> = Li and Cu) as New Oxygen Ion Conductors: Theoretical Assessment and Experiment

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.