In this paper we report the synthesis of a new phase in the La-Ti-Al-O system. A starting composition La2TiAlO6.5 and synthesis conditions of 1400 degrees C under H-2/Ar (5%/95%) resulted in a perovskite with a monoclinic (12/a; a = 7.686, b = 5.435, 5.424 Angstrom, beta = 90.20 degrees) cell. Although it was necessary to synthesize this material under reducing conditions, once prepared it was stable to subsequent oxidation at high temperatures in air, Structure refinement using neutron diffraction suggests the possible incorporation of a small amount of La on the small cation sites along with a La deficiency on the large cation sites, such that the composition may be written as La-0.83(La0.07Al0.465Ti0.465). (C) 1999 Academic Press.