Catherine Deudon

Charge Transfer in Misfit Layer Chalcogenides, [(MX)n]1+x(TX2)m: a Key for Understanding their Stability and Properties

Abstract Stability of misfit layer chalcogenides (M.L.C.) is always governed by a charge transfer (C.T.) mechanism. A comparison between M.L.C. and parent intercalated layered binary systems shows comparable characteristics, which illustrate the role of electron donor for the MX part (or its corresponding A-intercalant species) towards the TX2 acceptor part. In that way, intercalation chemistry within the vdW gap of multilayered TX2 misfit derivatives is also considered. The donor character of the MX part, easy to understand when trivalent M cations are present, can be also assumed if a divalent M cation is partly substituted for a trivalent one, as revealed from precise electron microprobe analysis. Examples of M.L.C. with enlarged MX part (with mixed M+II, M+III) emphasize the reality of the C.T. This M-to-T donor effect necessarily controls the transport and intercalation properties.

Synthesis and crystal structure of two new oxychalcogenides: Eu5V3S6O7 and La10Se14O

Abstract The crystal structure determination of two new oxychalcogenides, namely Eu 5 V 3 S 6 O 7 and La 10 Se 14 O, is reported. Eu 5 V 3 S 6 O 7 crystallizes in the orthorhombic symmetry (space group Pmmn ) with unit cell parameters (in A): a =17.463(2), b =3.6732(4), and c =10.007(1). This compound is isotypic with the Ln 5 V 3 S 6 O 7 compounds (Ln=La–Nd), and its structure has been refined to R 1=0.0248. Eu atoms, which are nine-coordinated by O and S atoms, are associated to form ribbons that are interconnected by [VS 4 O 2 ] octahedrons. La 10 Se 14 O crystallizes in the tetragonal symmetry (space group I 4 1 / acd ) with unit cell parameters (in A): a =15.926(2), and c =21.061(5). The structure was refined to R 1=0.0347. La 10 Se 14 O is isostructural with the Pr 10 X 14 O compounds (X=S and Se). The only structure difference is observed for one La site that is found split, in connection with a mixed O/Se site filling.

Synthesis and structure determination of the new Sm2Ti2O5S2 compound

Abstract Sm 2 Ti 2 O 5 S 2 was obtained in an attempt to prepare an oxysulfide of samarium and titanium in a way similar to the obtention of the quaternary Sm 3 NbO 4 Se 3 compound. The structure was determined by single-crystal X-ray diffraction. The following crystal data were obtained: M r = 540.6 g mol −1 , tetragonal symmetry with unit cell parameters a = 3.819(1) A, c = 22.964(5) A, space group I4/ mmm (139). Refinement for 127 unique reflections with I > 3σ(1), and 11 variables, converged to the reliability factor R = 1.77 %. The structure can be described as a stacking, along the c -direction, of [Sm 2 S 2 ] slabs of a rock-salt type (two-atom-thick-layers) separated by a 2D network of corner-sharing octahedra [= Ti 2 O 5 ] of a ReO 3 structure type.

XMCD sum rules at Cu2+L2, 3 edge

Abstract XMCD sum rules are checked through an analytical calculation of Cu2+ L2,3 edge. The sum rules are analytically satisfied as expected from the very general arguments developed in their derivation by Thole and Carra (1993). Analytical expressions for 〈Lz〉, 〈Sz〉 and 〈Tz〉 are obtained as functions of crystal field strength and spin-orbit coupling. The nullity of 〈Tz〉 is specially examined through group theory considerations.