Oxygen and fluorine doping in Sr2MnGaO5 brownmillerite

Systematic study on crystal chemistry of Sr2MnGaO5+delta layered perovskites upon variation of anion stoichiometry and the Mn oxidation state (V-Mn) was performed. Starting from fully oxygenated Sr2MnGaO5.5 compound, the samples with +3 less than or equal to V-Mn less than or equal to +4 were prepared either by a reduction of oxygen content at controlled partial oxygen pressure or by a partial replacement of oxygen by fluorine. Varying (5 is accompanied by structural transformations from Imma (0.03 less than or equal to delta less than or equal to 0.13, a approximate to c approximate to root2a(p), b approximate to 4a(p)) to Bmmm (0.41 less than or equal to delta less than or equal to 0.46, a approximate to c approximate to root2a(p) b approximate to 2a(p)) and to tetragonal P4/mmm (delta = 0.505, a approximate to a(p), c approximate to 2a(p)). The tetragonal Sr2MnGaO5-xF1+x oxyfluorides (a approximate to a(p), c approximate to 2a(p)) were prepared by treatment of Sr2MnGaO5.5 with XeF2. In the Sr2MnGaO4.78F1.22 structure the MnO6 octahedra are characterized by two short apical Mn-O distances and four long equatorial ones. This is interpreted as an "apically compressed" Jahn-Teller distortion, in contrast to the "apically elongated" one in Sr2MnGaO5+delta. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.