M. Julien-Pouzol

Systeme gallium-tellure: Diagrammes de phases, étude structurale de GaTe, Ga2Te5 et de Ga6SnTe10

Abstract Three phases are present in the GaTe system: Ga 2 Te 5 , Ga 2 Te 3 , and GaTe. Ga 2 Te 5 is stable in a narrow temperature domain, between about 400 and 495°C (its peritectic decomposition). The phase diagram is established from DTA and X-ray diffraction studies. The crystal structures of GaTe and Ga 2 Te 5 are described. The first one contains GaGa pairs and the second one a square plane coordination of Te, in which the atoms are bonded by covalency. The formation of compounds involving monovalent Ga is discussed, in connection with the existence of SnGa 6 Te 10 , in which Sn can be substituted by other monovalent or divalent cations.

Systems Ln2X3SnX2 (Ln = terres rares et X = S ou Se) composés Ln2SnS5, définition et étude structurale

Abstract In the ternary systems LnSnS, intermediate compounds are observed only in the quasi-binary Ln 2 S 3 SnS 2 sections. They have the general formula Ln 2 SnS 5 , and exist from La to Dy. They are orthorhombic, with the space group Pbam, and their structure was studied with single crystals of La 2 SnS 5 (Jaulmes 1974) and Sm 2 SnS 5 (Julien-Pouzol and Jaulmes 1976). These structures are extremely similar; they differ only by the coordination of the rare earth, which is 9 for La (with 2 relatively long bonds), and 8 for Sm. Intermediate compounds were not observed in the other regions of the ternary LnSnS systems. No ternary compound has been found in the LnSnSe systems.

Sur une famille de tellurures ternaires formes par le gallium avec l'etain II, le plomb ou l'indium I, de type SnGa6Te10

Two isostructural compounds are observed in the phase diagrams of the systems Ga2Te3-SnTe and Ga2Te3-PbTe. They have the general formula MGa6Te10 (M = Sn″ or Pb). They present a peritectic decomposition, at respectively 695 et 725°. The crystal structure is solved for SnGa6Te10. The rhombohedral cell, space group R32, contains 2 formulas ; a = 10.207 A, α = 89,74°. Gallium atoms are inside fully occupied tetrahedral sites. Tin atoms partially occupy, in a disordered way, 2 octahedral sites. The same structural type is observed for In2Ga6Te10, in which all the octahedral sites are filled.

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.

Crystal structure refinement of manganese thiogermanate Mn2GeS4

Abstract The crystal structure of Mn 2 GeS 4 was solved by X-ray diffraction, on a single crystal. It has the olivine type, orthorhombic Pnma , with a = 12.776, b = 7.441, c = 6.033A; R = 0.038 for 956 independent reflections.