We have synthesised a new n = 2 Ruddlesden-Popper (RP) system, (Sr-1 (-) La-x(x))(3)(Mg-1/3 (+) Nb-x/2(2/3) (-) (x/2))(2)O-7 (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 degrees C). 0 2013 Elsevier B.V. All rights reserved.