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.