The structure of a CaMnO3-δ perovskite single crystal was studied for the first time using thermal neutron diffraction at 300 to 840K. It was found that O vacancies in the crystal were ordered into 2 types of superstructure. A phase with a relative number of vacancies δ = 1/4 occupies the largest volume fraction of oxide (about 75%); the other volume was occupied by a superstructure with a lower vacancy content (δ = 1/5). The O deficiency in the crystal lattice was determined to be δ = 0.238. The mechanism of O vacancy ordering in the oxide was considered with regard to its charge state.

Ordering of Oxygen Vacancies in a CaMnO3−δ Perovskite Single Crystal. S.F.Dubinin, N.N.Loshkareva, S.G.Teploukhov, Y.P.Sukhorukov, A.M.Balbashov, V.E.Arkhipov, V.D.Parkhomenko: Physics of the Solid State,  2005, 47[7], 1267-72