title: Ca3Mn2O7.
abstract: The tricalcium dimanganese heptaoxide (Ca3Mn2O7) member of the Ruddlesden-Popper series Ca(n+1)Mn(n)O(3n+1), i.e. with n = 2, was previously reported with an I-centred tetragonal lattice [a(t) = 3.68 and c(t) = 19.57 A] by Fawcett, Sunstrom, Greenblatt, Croft & Ramanujachary [Chem. Mater. (1998), 10, 3643-3651]. It is now found to be orthorhombic, with an A-centred lattice [a = 5.2347 (6), b = 5.2421 (2) and c = 19.4177 (19) A]. The structure has been refined in space group A2(1)am using X-ray single-crystal diffraction data and assuming the existence of twin domains related by the (1-10) plane. A comparison with the basic perovskite structure CaMnO3 (n = infinity) is proposed.
authors.affiliation: Laboratoire CRISMAT, ISMRA et Université de Caen, 6 Boulevard du Maréchal Juin, 14050 Caen CEDEX, France. guiblin@ismra.fr
authors.forename: Nicolas
authors.initials: N
authors.lastname: Guiblin
authors.forename: Dominique
authors.initials: D
authors.lastname: Grebille
authors.forename: Henri
authors.initials: H
authors.lastname: Leligny
authors.forename: Christine
authors.initials: C
authors.lastname: Martin