M.F. Gorius

Structure cristalline de la phase β-KEr2F7. Composés isotypes

Abstract Potassium erbium fluoride β-KEr 2 F 7 crystallizes in the orthorhombic system, space group Pna 2 1 , with the unit-cell dimensions a = 11.820, b = 13.333, c = 7.816A ( Z = 8). The crystal structure has been solved from single-crystal diffractometer measurements (Ag Kα ) by Patterson and Fourier syntheses and refined by a least-squares method. The final R value is 0.042 for 2374 independent observed reflections ( R W = 0.051). The four species of erbium atoms are surrounded by eight fluorine atoms. These fluorine atoms form, respectively, three quadratic antiprisms and one dodecahedron, derived from a distorted cube. Two antiprisms and the dodecahedron share two of their faces to form (Er 3 F 17 ) 8− groups. These groups are bidimensionally linked and the planes they form are joined together by the third antiprism. A three-dimensional network is then produced, in the tunnels of which potassium atoms are located. Lattice parameters of compounds which are isotypic to the new structure type of β-KEr 2 F 7 are given.

Etude du system KF-ErF3

Abstract The phase diagram of the KF-ErF 3 system shows the existence of the five compounds K 3 ErF 6 , K 2 ErF 5 , KErF 4 , KEr 2 F 7 and KEr 3 F 10 . We give their X-ray single crystal and powder data (except for K 2 ErF 5 ). • - The monoclinic phase K 3 ErF 6 is closely related to the perovskite structure and • - The three others are closely related to the fluorite-type structure.

Etude du systeme RbFErF3

Abstract The phase diagram of the RbF-ErF3 system shows the existence of the four compounds Rb3ErF6, Rb2ErF5, RbEr3F10 and RbEr2F7. We report the X-ray powder data for the three first ones and X-ray single crystal data for RbEr2F7.

Structure cristalline de la phase β-KYb2F7

Abstract β-KYb2F7 crystallizes in the monoclinic system with parameters a = 6.528(1) A, b = 4.217(1) A, c = 6.435(1) A, β = 115°.94, Z = 1, and space group P2. The structure has been solved from single-crystal automatic four-circle diffractometer data by three-dimensional Patterson and Fourier syntheses and refined by a least-squares method. The final R value is 0.040. Structural relations with KLu2F7 are shown. These structures are characterized by chains of edge-sharing semiregular pentagonal bipyramids fused together by corner sharing in two directions perpendicular to the chains. Large tunnels, in which potassium atoms are located, are formed by the stacking of these planes.

Structure cristalline de K0,265Gd0,735F2,47

K0.265Gd0.735F2.47, the extreme member (2ac = 0.47) of the series KO.5-JCG<1O.5+XF2+2X of ordercd anion excess fluorite-related structures crystallizes in the orthorhombic space group Immm, with the xmit cell dimensions: a = 11.652(4) A, 6 = 8.152(2) Ä, c = 32.57(1) Ä, Z = 64. Structure analysis shows the presence of Gd6F37 groups. They consist of an arrangement of six GdFg Square antiprisms sharing comers which Surround a cuboctahedron of anions with an additional anion at its center. The GdeFsv groups are distributed in an ordered manner within a fluoritetype matrix and form chains parallel to the b direction. These chains altemate with edge-shared GdFg cubes chains to form layers running perpendicular to the a direction. The layers are connected by the distorted polyhedra surrounding potassium and the mixed-cation [Ko.62Gdo.38]-

Etude des systems CsF-ErF3 et CsF-YbF3

Abstract The phase diagrams of the CsF-ErF 3 and CsF-YbF 3 systems show the existence of the two compounds Cs 3 LnF 6 and CsLn 2 F 7 , like in the other systems CsF-LnF 3 with Ln = Ce, Sm, Eu, Gd, Dy and Ho. But with YbF 3 , we show the existence of three other phases related to α-UO 3 , one of which corresponds with the formula CsYb 3 F 10 . We report the X-ray powder data for all these phases.

Surstructures de type fluorine observées dans les systèmes KFLnF3 (Ln = Pr … Er)

Abstract Phases having fluoride-related superstructures are determined in the system K0,5−xLn0,5+xF2+2x (0.33 a ≈ a F √6, b ≈ a F √2, c ≈ 3a F √2 , β = 125°). (ii) 0,33 0,45, orthorhombic system, Immm, a ≈ 2aF, b ≈ aF√2, c ≈ 4aF√2). (iii) 0,33 C2 m , a ≈ 2a F √3, b ≈ a F √2, c ≈ 1 2 a F √114 , β ≈ 97°).

Structure cristalline de NaLiYb2F8: Composes isotypes

Abstract NaLiYb 2 F 8 crystallizes in the monoclinic system, space group C2 c , with a = 10.3516(9), b = 8.2069(9), c = 6,9674(7) A, β = 90°, Z = 4. The crystal structure has been solved from single crystal diffractometer measurements (Ag Kα radiation) using Patterson and Fourier syntheses and refined by a least-squares method. The final R value is 0.021 for 1756 independent observed reflections. Two YbF 8 polyhedra share one of their edges to form Yb 2 F 14 groups which are three-dimensionally linked and create cavities in which Na and Li are located. Yb 2 F 14 groups share two of their edges with these of one NaF 7 (or NaF 9 ) polyhedron to form Y 2 NaF 20 blocks. As well, the structure may be described by the packing of planes formed by these two-dimensionally linked blocks. The description of this structure is compared with that ascribed to NaLiY 2 F 8 , which has been described in the monoclinic system, space group P2 1 m , with a′ = ( a + b )/2, b′ = c , c′ = ( b − a )/2, Z = 2. It is shown that positions of the atoms confer pseudoorthorhombic symmetry on the cell. Lattice parameters of isotypic compounds are given in the pseudoorthorhombic lattice and they are compared with those recently published with the structure described in the monoclinic system, space group P2 1 m .

Etude par diffraction neutronique de la phase “Cs4−xYb12F40−x” (0 ≤ x ≤ 1): Hypothèse structurale

Abstract The structure of the phase Cs4−xYb12F40−x(0 ≤ x ≤ 1) has been determined by a single-crystal neutron diffraction study. It has been solved in the space group P63mc and refined to the best R factor of 0.0535 for the formula Cs3.4Yb12F39.4 (324 independent reflections). Three edge-sharing pentagonal bipyramids surrounding three ytterbium atoms form Yb3F16 groups and the structure is described as the superposition, according to the sequence A1A2B1B2A1A2…, of sheets of corner-sharing Yb3F16 groups with a possible transformation of bipyramids into octahedra in the A2 and B2 layers. These sheets are joined together by the axial fluorine atoms of the bipyramids or octahedra. Cesium atoms are located in the tunnels formed by their stacking. It is shown that the Cs4−xYb12F40−x phase (0 ≤ x ≤ 1) is an intermediate step of the Cs4−xYb12F40−x solid solution observed with 0 ≤ x ≤ 2 and corresponds to a superstructure of the high-temperature YbF3 phase.

Composes quadratiques KMeIILn3F12

Abstract The phase diagram of the KMnF3ErF3 system shows the existence of the only one compound KMnEr3F12. This compound has a tetragonal cell with a = 8,118 A, c = 11,517 A, Z = 4. Systematical extinctions are observed only for (hk l>) with h+k+l = 2n+1. We give lattice parameters for 16 new isotype compounds KMeLn3F12 with Me = Mg, Zn, Ni and Co, Ln = Y and all the rare earths, and d-spacings and intensities for five of them.