A synchrotron X-ray powder diffraction and high-resolution electron microscopic study was made of structural arrangements in the -phase. The powder diffraction data, as well as high-resolution electron microscopy, showed that the basic structure of this phase exhibited cubic symmetry (P4332), whereas an ordered distribution of the cation vacancies on the octahedral positions resulted in the formation of a tetragonal superlattice (P41212).

A.N.Shmakov, G.N.Kryukova, S.V.Tsybulya, A.L.Chuvilin, L.P.Solovyeva: Journal of Applied Crystallography, 1995, 28[2], 141-5