Jérôme Dugué

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.

Ferro- and antiferromagnetism in oxychalcogenides LnCrOX2 (Ln = La or Nd and X = S or Se)☆

The two isomorphous compounds LaCrOS2 and LaCrOSe2 are ferromagnetic (Tc = 35 and 51 K, respectively). This implies ferromagnetic super-superexchange interactions. NdCrOS2 is antiferromagnetic (TN = 72 K) and undergoes a spin-flop transition (Hc = 54 KOe at 20 K). The study of the thermal variation of Cr3+ and Nd3+ magnetic moments below TN allows a rough estimate of the CrNd and CrCr exchange fields ratio (∼0.1).

Study of the Ag-In-Te ternary system. II. Description of the quadrilateral Ag-Ag2Te-In2Te3-In

Abstract The phase diagram of the Ag–Ag 2 Te–In 2 Te 3 –In system was studied by DTA, DSC, XRD, metallography and electron microprobe methods. With the exception of the three known compounds, AgInTe 2 , AgIn 5 Te 8 and Ag 3 In 97 Te 147 that are localized in the Ag 2 Te–In 2 Te 3 quasi-binary section, no other ternary compounds are identified. The eutectic valleys are drawn, and the nature and the location of the ternary invariants are given. Twelve ternary invariants are found: three eutectic points, eight transitory peritectic points and one metatectic point. One ternary liquid–liquid miscibility gap is identified: it originates from the Ag–Ag 2 Te system and overlaps a large region of the Ag–Ag 2 Te–InTe–In system; it is crossed by a eutectic valley, giving a first-class ternary monotectic equilibrium. No glassy region is observed.

Description of the Cu-As-Se ternary system

Abstract The phase diagram of the Cu-As-Se ternary system was studied by differential thermal analysis, X-ray diffraction and metallography analysis. Two ternary phases are observed: the Cu 3 AsSe 4 compound, which melts congruently, and the CuAsSe 2 compound, which undergoes a peritectic decomposition. The ternary system is subdivided into 12 secondary triangles. The 12 ternary invariants are localized: six eutectics, one of which is degenerated at the selenium apex, and six peritectics. Two ternary liquid-liquid miscibility gaps originating from the Cu-Se binary system are identified. One of these is crossed by a eutectic valley giving a first-class ternary monotectic equilibrium. A large vitreous region, which comes from the As-Se binary glass zone, is identified; it overlaps the liquid-liquid miscibility area, giving phase-separated glasses.

Description du système ternaire AgSbSe

Abstract The phase diagram of the AgSbSe system was studied by differential thermal analysis, X-ray diffraction and metallography analysis. Two ternary phases were observed: the AgSbSe 2 compound, an f.c.c. NaCl-like structure with congruent melting and a new phase, to which the formula Ag 3 Sb 7 Se 12 is attributed. This last compound is dimorphic and the transition between the two forms occurs at about 200 °C. The high temperature structure disappears at about 360 °C. Four quasi-binary sections are described in this ternary system. Seven ternary invariants are characterized: five eutectics of which two are degenerated at the selenium apex, and two peritectics. In the temperature range between 360 and 558 °C, besides the seven three-phase domains, there are five two-phase domains. Three ternary liquid-liquid miscibility gaps are observed, of which only two are crossed by a valley. Finally, a glass domain with a small extension, which comes from a binary glass zone rich in selenium of the SbSe system, was established within the (AgSbSe 2 )SeSb 2 Se 3 triangle.

Les combinaisons U2R2n−2O2nSn+1 formées par les lanthanides légers (R=Ce à Tb) avec n=2 et 3 et dans le cas du lanthane avec n=2 à 6

Abstract Two series of compounds are described with the light lanthanides (from La to Tb) with n = 2 and 3. They are obtained by direct union at 1400°C of R 2 O 2 S and UOS. The n = 2 series, of U 2 R 2 O 4 S 3 composition, is isostructural with Ce 4 O 4 S 3 (or Ce IV 2 Ce III 2 O 4 S 3 ). The n = 3 series, of U 2 R 4 O 6 S 4 composition, is isostructural with Ce 6 O 6 S 4 (or Ce IV 2 Ce III 4 O 6 S 4 ). The orthorhombic structures of these compounds result in periodic sheers in the structural array of hexagonal R 2 O 2 S. The crystal parameters of the two series of compounds are determined. In the case of lanthanum, compounds are formed by periodic sheers having longer periods than the preceding ones. All the terms from n = 2 to n = 6 are described and their crystal parameters are determined.

Twins in LaSe2 and LaSe2−x and a Phase Transition in LaS2

The rare earth dichalcogenide structures are derived from a common type, the tetragonal anti Fe2As-type (P4/n mm). All of these structures have layers of (LaX) n n+ (X = S, S3) that alternate with chalcogen layers (S or Se)n. They are assembled with a pseudo-tetragonal symmetry. In the layers of S or Se, the atoms form covalent pairs.

Magnetic structure of PrCrOS2

Abstract PrCrOS 2 is antiferromagnetic with T N = 83 K. The magnetic space group is B p 2′ m′ . The variations of μ Cr and μ Pr with temperature were studied. The properties of PrCrOS 2 are very similar to those of NdCrOS 2 .

Les combinaisons U2R2n−2O2nSn+1 formées par les lanthanides légers (R = Ce à Tb) avec n = 2 et 3 et dans le cas du lanthane avec n = 2 à 6

Abstract Two series of compounds are described with the light lanthanides (from La to Tb) with n = 2 and 3. They are obtained by direct union at 1400°C of R 2 O 2 S and UOS. The n = 2 series, of U 2 R 2 O 4 S 3 composition, is isostructural with Ce 4 O 4 S 3 (or Ce IV 2 Ce III 2 O 4 S 3 ). The n = 3 series, of U 2 R 4 O 6 S 4 composition, is isostructural with Ce 6 O 6 S 4 (or Ce IV 2 Ce III 4 O 6 S 4 ). The orthorhombic structures of these compounds result in periodic sheers in the structural array of hexagonal R 2 O 2 S. The crystal parameters of the two series of compounds are determined. In the case of lanthanum, compounds are formed by periodic sheers having longer periods than the preceding ones. All the terms from n = 2 to n = 6 are described and their crystal parameters are determined.

Les combinaisons U2R2n−2O2nSn+1 formées par les lanthanides légers () avec n = 2 et 3 et dans le cas du lanthane avec

Abstract Two series of compounds are described with the light lanthanides (from La to Tb) with n = 2 and 3. They are obtained by direct union at 1400°C of R 2 O 2 S and UOS. The n = 2 series, of U 2 R 2 O 4 S 3 composition, is isostructural with Ce 4 O 4 S 3 (or Ce IV 2 Ce III 2 O 4 S 3 ). The n = 3 series, of U 2 R 4 O 6 S 4 composition, is isostructural with Ce 6 O 6 S 4 (or Ce IV 2 Ce III 4 O 6 S 4 ). The orthorhombic structures of these compounds result in periodic sheers in the structural array of hexagonal R 2 O 2 S. The crystal parameters of the two series of compounds are determined. In the case of lanthanum, compounds are formed by periodic sheers having longer periods than the preceding ones. All the terms from n = 2 to n = 6 are described and their crystal parameters are determined.