K0.53Mn2.37Fe1.24(PO4)3

Abstract

During an attempt to crystallize potassium manganese diiron phosphate KMnFe2(PO4)3 by the flux method, a new phase, potassium dimanganese iron triphosphate, K0.53Mn2.37Fe1.24(PO4)3, was isolated. This phase, whose composition was confirmed by ICP analysis, is isotypic with the alluaudite-like phosphates, thus it exhibits the (A2)(A′2)(A1)(A′1)(A′′1)(M1)(M2)2(PO4)3 general formula. The site occupancies led to the following cation distribution: 0.53 K on A′2 (site symmetry 2), 0.31 Mn on A′′1, 1.0 Mn on M1 (site symmetry 2) and (0.62 Fe + 0.38 Mn) on M2. The structure is built up from infinite chains of edge-sharing M1O6 and M2O6 octahedra. These chains run along [10overline{1}] and are connected by two different PO4 tetrahedra, one of which exhibits 2 symmetry. The resulting three-dimensional framework delimits large tunnels parallel to [001], which are partially occupied by the K+ and Mn2+ cations.