P. Laruelle

Oxysulfides and oxyselenides in sheets, formed by a rare earth element and a second metal

Abstract The preparation and structural features of compounds of the general formula (R O) n (M x X y ) , with R =rare earth, M =IB, IIIA, IVA, or VA elements, and X =S or Se, are described. Four families of oxysulfides can be prepared by the reaction of a rare earth oxysulfide and a post-transition metal sulfide. These include (R O) 4 Ga 2 S 5 for R =Ce(tetragonal P4/mmm ) and R =Pr to Sm(orthorhombic Pbca of the type (NdO) 4 Ga 2 S 5 ); (R O) 4 Ca 1.33 S 4 for R =La and Ce(tetragonal P4/mmm ); (R O) 4 Ge 1.5 S 5 for R =La to Nd(orthorhombic Pbca type (NdO) 4 Ga 2 S 5 ); (R O) 4 Sn 2 S 6 for R =La to Nd(orthorhombic pbnm type (LaO) 4 Sn 2 S 6 ). The reaction of lanthanum oxyselenide and the metal selenide gives (LaO)GaSe 2 , (LaO)InSe 2 , (LaO) 4 Ge 1.5 Se 5 , (LaO) 4 Sn 2 Se 6 , and (LaO)SbSe 2 . Crystal data are given for these systems. Although these compounds crystallize in several different space groups, they all have sheet structures formed by alternation of an oxide sheet ( R O) and a sulfide or selenide sheet ( M x X y ). They belong to 7 new structural types. The ( R O) sheets have the same tetragonal or pseudotetragonal array of R 4 O tetrahedra, but the ( M x X y ) sheets have various structures, with 2, 3, or 4 layers of X atoms. The structural characters of these compounds are discussed.

Oxysulfides formed by a rare earth and a second metal: II. Shear structures

Abstract Many of the oxysulfides containing two metals have layered structures of ( R O) sheets and ( M x S y ) sheets ( R = rare earth, M = Cu, Ag, Ga, In, Ge, Sn, As, Sb, Bi). In the new compounds (La 4 O 3 )(AsS 3 ) 2 and (La 5 O 3 )In 6 S 17 , parallel ribbons of stoichiometry (La 4 O 3 ) and (La 5 O 3 ) substitute for the (LaO) sheets. The formation of ribbons is explained by shear mechanisms involving two different orientations of the periodic shear planes in the tetragonal (LaO) sheet. In a third compound La 3 GaS 5 O or (La 2 O)LaGaS 5 , the formation of (La 2 O) ribbons involves similar shear mechanism. All these shear structures preserve the main characters of the layered oxysulfides: oxygen is only bound to lanthanum, and the second metal is only bound to sulfur.

Oxysulfure de scandium Sc2O2S

Abstract Sc2O2S is hexagonal, P6 3 mmc , a = 3.5196(4) A, c = 12.519(2) A, Z = 2, Dc = 3.807 g cm−3, Dm = 4.014 g cm−3, μ(MoKα) = 55.51 cm−1. The final R value is 0.038 for 205 symmetry-independent reflections. This scandium oxysulfide has c = 12.52 A, twice the value found in rare earth oxysulfides. An La2O2S cell combined with its reflection in a (001) mirror gives the Sc2O2S cell.

Structure moyenne d'un oxyse´le´niure de lanthane et gallium (LaO)4Ga1,88Se4,82

In a first approach, satellite reflections observed on the X-ray diffraction diagrams are neglected and an average picture of the structure of the tetragonal compound (LaO)4Ga1,88Se4,82 is presented (a = 4.178(1)A,c = 19.546(1)A, space groupI4/m mm Z = 1, D°c = 5.6g/cm3; refining structural agreement indexR = 0.06). The structure is built up of alternating (LaO) and(Ga0.94Se2.41) layers parallel to the (001) plane. This average structure is closely related to that of (CeO)4Ga2S5.

A new family of sheet structures: the oxyselenides formed by a rare earth and a second metal

Abstract Sheet structures are observed in oxyselenides formed by La and a second metal of the IIIA - VA groups of the periodical classification. (LaO) 4 Ge 1.5 Se 5 : orthorhombic cell of the (NdO) 4 Ga 2 S 5 type, with disordered arrangement of Ge atoms on the Ga sites. (LaO) 2 SnSe 3 : orthorhombic pseudo tetragonal cell of the (LaO) 2 SnS 3 type. (LaO)SbSe 2 : tetragonal cell of the (CeO)BiS 2 type. All this structures are formed by alternating (LaO) sheets and (M x Se y ) sheets (M = second metal). The (LaO) sheets are formed by La 4 O tetrahedra which share 4 of their 6 edges in a tetragonal or pseudo tetragonal arrangement. The (M x Se y ) sheets are formed by 2,3 or 4 layers of Se atoms. The M atoms are only bonded to Se atoms, in octahedral (Sb) or tetrahedral (Ga, In, Ge, Sn) arrangements. Similar compounds are not obtained with the other rare earths. The structure of (LaO)GaSe 2 , which is only observed with selenides, is described: the cell is orthorhombic space group P 2 1 ab; a = 5.951(3); b = 5.963(3); c = 12.256(7) A; Z = 4; d x = 5.84 Mg m −3 ; M (MoKα) = 31.3 mm −1 . The structure was established on single crystal data and refined by a least-squares procedure; the final R value is 0.07 on 523 independent reflections. The structure is formed by alternating (LaO) and (GaSe 2 ) layers, parallel to the (001) plane.