Sr₂MgMoO_6-δ: Structure, phase stability, and cation site order control of reduction

The potential solid oxide fuel cell anode material Sr₂MgMoO ₆ adopts a √2 × √2 × 2I1̄ superstructure of the simple perovskite cell, derived from an a⁰a⁰c ^- tilt system via distortion of the Mg- and Mocentered octahedra. Reduction of Sr₂MgMoO₆ appears to be correlated with antisite disorder at either point or extended antiphase defects. The degree of reduction is small at temperatures below 900 °C. Upon further reduction above 900 °C, Sr₂MgMoO₆ begins to decompose into a reduced material modeled as an n = 2 Ruddlesden-Popper phase with a significantly higher Mo:Mg ratio, MgO, and Mo. Diffraction data are consistent with the reduced material being significantly intergrown with the perovskite matrix.