A neutron diffraction study of the temperature dependence of Ca2Fe2O5

The crystal structure of Ca2Fe2O5 has been studied as a function of tempera ture up to 1000 degrees C. Cell parameters vary linearly with temperature w hile a structural phase transition from Pcmn to Icmm takes place at about 7 00 degrees C. The transition induces a change in the tilting of the octahed ra and displacements of the oxygen ions in the tetrahedra that build up the structure in alternating layers. Increasing disorder along the chains of t etrahedra and ordering of the octahedra and coordination polyhedron around Ca are observed in the high temperature structure. The magnetic structure w as refined in space group Pcm'n'. Comparisons are made to the structures of Sr2Fe2O5 and other doped brownmillerite phases. (C) 1999 Elsevier Science Ltd.