Structural transformation and oxidation of Sr 2MnO 3.5+x determined by in-situ neutron powder diffraction

Abstract

The oxidation of the n = 1 Ruddlesden-Popper phase, Sr 2MnO 3.5+x, where 0 ≤ x ≤ 0.5 has been investigated using a combination of in-situ diffraction techniques. In agreement with previous reports the room temperature structure of Sr 2MnO 3.5+x was determined to be monoclinic crystallising in space group P2 1/c . On heating in air the material undergoes rapid oxidation at a relatively modest temperature, ∼275 °C. The oxidation process is coincident with a significant change in the structure, with the material now adopting a tetragonal I4/mmm structure. In the oxygen deficient phase where x > 0 the Mn coordination is square pyramidal, with a sixth partially occupied oxygen position giving rise to octahedral coordination. Oxidation of Sr 2MnO 3.5+x results in the filling of the partially occupied O4 positions and a resulting increase in symmetry, with the Mn coordination now adopting solely a distorted octahedral environment.