High oxide ion conducting solid electrolytes of bismuth and niobium co-substituted La2Mo2O9

•La2−xBixMo2−xNbxO9−δ (LBMN) ceramics are synthesized via solid state reaction.•The LBMN system exhibits high electrical conductivities at high temperature and low thermal expansion.•Their structures are studied by Rietveld refinements of the XRD patterns and TEM.•A modified Debye relaxation approach is employed to learn the ion dynamics.•Their properties are closely related to the crystallographic characteristics based on [O1La3Mo] tetrahedral units.

Bismuth and niobium co-substitutions on lanthanum molybdate with the nominal formula La2−xBixMo2−xNbxO9−δ (x = 0–0.24) (LBMN) are synthesized via solid state reaction. Their structures and properties are studied by powder X-ray diffraction (XRD), thermal analysis, electron diffraction, and impedance spectroscopy. XRD experiments and thermal analysis demonstrate the stabilization of the high temperature cubic phase when x ≥ 0.04. Studies of the polar area in electron diffraction confirm the inhomogeneous nature of the composition. A modified Debye relaxation approach is employed to learn the ion dynamics, and it shows non-monotonic functions in relaxation parameters τ0 and the activation energy Ea, which is in agreement with the volume variation of the basic [O1La3Mo] tetrahedral as a new structural description. As a result, the LBMN system exhibits good performance in electrical conductivities at high temperature, and shows a decrease of the average thermal expansion coefficients (TECs) along the dopant content.