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

Bismuth and niobium co-substitutions on lanthanum molybdate with the nominal formula La_2-xBi_xMo_2-xNb_xO_9-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 E_a, 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.