Studies on nonstoichiometry of Ca2MnxFe2−xO5+δ

The structure of Ca₂Mn_xFe_2?xO_5+δ (0 ≤ x ≤ 0.5), in which δ was determined by thermogravimetric and chemical analyses, was investigated by means of X-ray diffraction and Mőssbauer effect measurements. Increase of δ was accompanied with increase of both tetravalent manganese ion and octahedral site and decreased the lattice parameter b_o. in the brownmillerite structure. Anomalous variation of the b_o with δ was explained to be due to the Jahn-Teller distortion caused by Mn³⁺. Above a certain value of δ, the brownmillerite phase changed into an ordered phase which has the lattice parameters a_o = a_dical, b_o = 2b_dical and C_o = 2C_dical. In the phase portion of iron ions was tetravalent.