Sr₂MgMoO_6-δ: Structure, Phase Stability, and Cation Site Order Control of Reduction

The potential solid oxide fuel cell anode material Sr 2 MgMoO 6 adopts a √2 × √2 × 2 I1̄ superstructure of the simple perovskite cell, derived from an a 0 a 0 c - tilt system via distortion of the Mg- and Mo-centered octahedra. Reduction of Sr 2 MgMoO 6 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, Sr 2 MgMoO 6 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.