Ordering of oxygen vacancies in a CaMnO3 − δ perovskite single crystal

The structure of a CaMnO_{3 ? δ} perovskite single crystal was studied for the first time using thermal neutron diffraction in the temperature range 300–840 K. It was detected that oxygen vacancies in the crystal are ordered into two types of superstructure. A phase with a relative number of vacancies δ = 1/4 occupies the largest volume fraction of oxide (～75%); the other volume is occupied by a superstructure with a lower vacancy content (δ = 1/5). The oxygen deficiency in the crystal lattice was determined to be δ = 0.238. The mechanism of oxygen vacancy ordering in the oxide is discussed taking into account its charge state.