Marie-Paule Pardo

Structure cristalline du polytype FeGa2S4α 1T

Abstract The crystal structure of the low temperature form of α-FeGa 2 S 4 1T (with a = 3,654(2) A ; c = 12,056(7) A ; Z = 1, space groupe P3m1) has been refined by a least squares method to a final R = 0.051 with 180 independant reflections. The sulfur stacking sequence in this polytype is…BCBC…Fe atoms occupy the octahedral voids and Ga atoms the tetrahedral voids.

Determination des structures des formes α et β de Ga2S3 structural determination of α and β Ga2S3

Resume The structures of αGa 2 S 3 and βGa 2 S 3 were refined in order to establish the exact cationic distribution. The R factors are 0.046 for αGa 2 S 3 and 0.049 for βGa 2 S 3 . βGa 2 S 3 is of wurtzite type and αGa 2 S 3 is found to be a superstructure of βGa 2 S 3 with a partial occupation of the three cationic sites.

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.

Etude des systems Ga2S3-CoS et Ga2Se3-CoSe

The system Ga2S3-CoS is studied by D.T.A., metallography and X-rays diffraction. Several phases are observed. First, from n = 0.05 to n = 0.14, (n = Co(at)Co(at)+Ga(at), a wurtzite type solid solution. It is a metastable phase obtained by quenching the melt. It does not belong to the phase diagram. In the phase diagram, three phases are observed: 1- From n = 0.09 to n = 0.16, a blende superstructure. Its peritectic decomposition is at 1030°C. 2- For n = 0.33 a CoGa2S4 compound. It is dismorphous with CdGa2S4 type at low temperature and ZnAl2S4 type at high temperature. It is transformed, by a syntectic reaction at 1178°C, in a mixture of two liquids. The system Ga2Se3-CoSe has no intermediate phase.

Verres formes par les oxysulfures de terres rares Ln2O2S

Abstract Glass formation in the Ln 2 O 2 S-Ga 2 S 3 systems (Ln = La to Nd). Preparations. Extent of the glassy regions as a fonction of the R.E. content and of the nature of the R.E. : Vitreous transition temperatures and crystallization temperatures. Microhardness. Optical properties.

Polymorphisme de Ga2S3 et diagramme de phase GaS polymorphism of Ga2S3 and phase diagram of GaS

Abstract The monoclinic form α′ Ga2S3 is exactly stoechiometric and is stable from room temperature to melting. The hexagonal form α and the wurtzite-type form β exist only at high temperature, above 885°C; their formation requires a very small defect of sulphur and consequently their are obtained in presence of GaS. The passage from the hexagonal form to the wurtzite form is progressive and depends on the proportion of GaS. The blende-type form is clearly sub-stoechiometric (GaS1.38) and only exits in a small domain of temperature. The phase-diagram is described from GaS0.96 to GaS1.56.

Etude des proprietes magnetiques, Mössbauer et electriques du compose lamellaire FeGa2S4α 1T

Abstract FeGa 2 S 4 α 1T shows a lamellar crystal structure characterized by an alternative localization in host sulfur framework of Fe,Ga and vacancies planes parallel to the c axis of the unit cell. Single crystals have been obtained by chemical vapor transport reaction with I 2 or Cl 2 as transporting agent. Magnetic, mossbauer and electrical experiments were performed on single crystals. Magnetic susceptibility deviates from the Curie-Weiss behaviour in explorated temperature range 4.2–300 K but the high temperature asymptote indicates a probable Fe 2+ high spin state. At approximately 17 K susceptibility shows a maximum which is corrolated to an antiferromagnetic ordering at low temperature. Magnetic properties are discussed in the view of a two dimensional model. Electrical properties are in agreement with semiconducting state; mobility of the charge carriers is low.

Verres d'oxysulfures de terres rares conducteurs ioniques

Abstract Glass formation in the ternary system La 2 O 2 S-Ag 2 S-Ga 2 S 3 . Preparation. Extent of the glassy region in the ternary diagram. Thermal behaviour and electrical properties of the glasses. The electrical conductivity is essentially depending on the Ag content.

Etude des phases metastables I - Cas du système Ga2S3CdS: Study of metastable phases; I - Ga2S3CdS system

Abstract Tetrahedral metastable phases are obtained by quenching from the liquid state, for n = 0.03 − 030 ( n = Cd ( Cd + Ga ) ) . These phases come back to the equilibrium state by a two steps process with two exothermic transitions. In the first step, other tetrahedral non-equilibrium phases are formed. In the second step appear the characteristic phases of the equilibrium phase diagram.

Verres formes dans les systemes Ga2S3La2X3MnS (X = S, O)

Abstract Preparation of glasses. Glass forming domains in the ternary systems [Ga 2 S 3 , (La 2 S 3 , La 2 O 2 S or La 2 O 3 ), MnS]. Thermal behaviour. U.V. and visible spectroscopy. E.P.R. spectra. Manganese has an octahedral environment of sulfur.