A neutron diffraction study of the temperature dependence of Ca2Fe2O5

The crystal structure of Ca2Fe2O5 has been studied as a function of temperature up to 1000 degrees C. Cell parameters vary linearly with temperature while a structural phase transition from Pcmn to Icmm takes place at about 700 degrees C. The transition induces a change in the tilting of the octahedra and displacements of the oxygen ions in the tetrahedra that build up the structure in alternating layers. Increasing disorder along the chains of tetrahedra and ordering of the octahedra and coordination polyhedron around Ca are observed in the high temperature structure. The magnetic structure was refined in space group Pcm'n'. Comparisons are made to the structures of Sr2Fe2O5 and other doped brownmillerite phases. (C) 1999 Elsevier Science Ltd.