Crystallographic study of lanthanum aluminate by convergent-beam electron diffraction

Abstract

The space group of a well annealed LaAlO3 crystal, determined by convergent-beam electron diffraction, is Fm\overline 3c. Lower-symmetry monoclinic and triclinic phases have also been observed in not so well annealed and as-grown crystals. The cubic structure with Fm\overline 3c symmetry arises from a side-doubling transformation of the cubic perovskite structure due to the tilting of oxygen octahedra. Lower-symmetry phases are associated with the distortion of the cubic lattice due to oxygen deficiency or strain in the crystal. The previously reported R\overline 3c space group is probably due to the coexistence of the cubic phase and a lower-symmetry phase in the same crystal.