Synthesis of novel Ruddlesden–Popper compounds, (Sr1 − xLax)3(Mg1/3 + x/2Nb2/3 − x/2)2O7 (0.15 ≤ x ≤ 0.33)

•The double-perovskite Sr2MgMoO6 is a promising SOFC anode material.•Here we report a related new Ruddlesden–Popper phase (Sr,La)3(Mg,Nb)2O7.•It forms with the composition, (Sr1 − xLax)3(Mg1/3 + x/2Nb2/3 − x/2)2O7 (0.15 ≤ x ≤ 0.33).•Structure analysis reveals orthorhombic symmetry and B-site cation ordering.•The phase is stable under both reducing and oxidising conditions.

We have synthesised a new n = 2 Ruddlesden–Popper (RP) system, (Sr1 − xLax)3(Mg1/3 + x/2Nb2/3 − x/2)2O7 (0.15 ≤ x ≤ 0.33). Crystal structure investigation of the system revealed orthorhombic lattice symmetry and ordering of the B-site cations, Mg and Nb. The new RP compounds were found to be stable in both highly reducing and oxidising conditions at relatively high temperatures (at least up to 1200 °C).