Conductivity of reduced La2Mo2O9 based oxides: The effect of tungsten substitution

The electrical properties of reduced LAMOX-type oxides (La_1.9Y_0.1Mo_2−yW_yO_9−δ with y = 0, y = 0.5, y = 1.0) were investigated by complex impedance spectroscopy.When reduced at 605 °C in hydrogen, La_1.9Y_0.1Mo₂O_9−δ is 10 times and 3 × 10⁵ times more conductive at 605 and 180 °C, respectively, than in air at the same temperatures. The conductivity curve presents a low slope (0.37 eV versus 1.2 eV in air).Besides, the stabilising effect of tungsten against reduction is evidenced, in good agreement with previous reports.In low oxygen partial pressures however (PO₂ < 10⁻¹⁸ Pa), the decomposition of the materials is detected, whatever the tungsten content (0 ≤ y ≤ 1 in La_1.9Y_0.1Mo_2−yW_yO_9−δ). This observation points out the efficiency limit of Mo⁶⁺/W⁶⁺ substitution to stabilise the structure against reduction, and the limit for an application as IT-SOFC electrolyte.However, given the high electronic conductivity upon reduction, the application of these materials in IT-SOFC electrodes could be considered.