G. Brun

The crystal structure of AgTIX phases (X = S, Se, Te)

Abstract The isomorphism of ternary compounds AgTIX (X = S, Se, Te) is pointed out. The compounds have an orthorhombic unit cell with four formulas and the space group is Pnam. The crystal structure of AgTlTe has been solved with a final R value of 0.098. Silver and tellurium atoms are covalently bonded in chains of AgTe4 tetrahedra delimiting channels where thallium atoms are located.

Structure et proprietes physiques des phases Cu2TlX2, Cu3 YTl2X4 (AVEC X = Se, Te et Y = Fe, Ga, Al)

Abstract Ternary (Cu 2 TlX 2 ) and quarternary (Cu 3 YTl 2 X 4 ) compounds (with X = Se, Te and Y = Fe, Ga, Al) have been prepared and characterized. All of them have the same lamellar structure where tetrahedras (CuYX 4 ) n and thallium atoms in coordination eight form successive layers. Some are metallic conductors (Cu 2 TlX 2 ) whereas others are semi-conductors (Cu 3 YTlX 4 ). The metallic behaviour could be due to thallium monovalent-thallium trivalent interactions within the layers.

Mise au point dans le ternaire TlBiTe. Existence de deux phases nonstoechiometriques de type TlBiTe2

Abstract The cross section BiTeTlTe of the phase diagram TlBiTe was constructed by X-ray, microstructure, and DTA methods. Two phases were emphasized: Tl1−xBi1+xTe2 with x = 0.06, and Tl1−yBi1+yTe2 with y = 0.2. The first one is a nonstoichiometric representation of what so many authors studied as TlBiTe2. The latter is a high-temperature phase which decomposes in eutectoid reaction (415°C): 1.18{ Tl 0.8 Bi 1.2 Te 2 } ⇄ Tl 0.94 Bi 1.06 Te 2 + 0.36 { BiTe } . The high-temperature form undergoes a phase transformation by quenching, giving a metastable low-temperature form. The discussion includes electrical resistivity and thermoelectric measurements of each of them.

Phase diagram equilibria In2Se3-Sb2Se3 crystal growth of the β-In2Se3 phase (In1.94Sb0.06Se3)

Abstract The phase diagram In2Se3–Sb2Se3 was constructed from DTA and X-ray diffraction analysis data. No compound was observed in it, but two finite regions of In2Se3-based solid solutions were found: the first one, called β′ (from 10 to 3.5 mol% Sb2Se3), of the tetradymite structure, and the second (from 3.5 to 0 mol% Sb2Se3) being the β-In2Se3 stabilized form. Crystals of the antimony-doped β-In2Se3 form were grown by the Bridgman method. This compound, the composition of which is In1.94Sb0.06Se3, appears to be closely connected with the tetradymite structure. The refined unit-cell parameters of the hexagonal cell are a = 397(2) pm and c = 2827(2) pm. Its room temperature dc conductivity is 2 × 10−2 Ωcm−1, and it is an n-type semiconductor with a band gap of 1.34 eV.The phase diagram In{sub 2}Se{sub 3}-Sb{sub 2}Se{sub 3} was constructed from DTA and X-ray diffraction analysis data. No compound was observed in it, but two finite regions of In{sub 2}Se{sub 3}-based solid solutions were found: the first one, called {beta}{prime} (from 10 to 3.5 mol% Sb{sub 2}Se{sub 3}), of the tetradymite structure, and the second (from 3.5 to 0 mol% Sb{sub 2}Se{sub 3}) being the {beta}-In{sub 2}Se{sub 3} stabilized form. Crystals of the antimony-doped {beta}-In{sub 2}Se{sub 3} form were grown by the Bridgman method. This compound, the composition of which is In{sub 1.94}Sb{sub 0.06}Se{sub 3}, appears to be closely connected with the tetradymite structure. The refined unit-cell parameters of the hexagonal cell are a = 397(2) pm and c = 2827(2) pm. Its room temperature dc conductivity is 2 {times} 10{sup {minus}2} {Omega}/cm, and it is an n-type semiconductor with a band gap of 1.34 eV.

Solid state demixing in Bi2Se3-Bi2Te3 and Bi2Se3-In2Se3 phase diagrams

Abstract The Bi 2 Te 3 -Bi 2 Se 3 and Bi 2 Se 3 -In 2 Se 3 systems were studied by differential thermal analysis and X-ray powder diffraction. The phase diagrams of these systems were constructed; they are quasi-binary. In both cases, there are wide ranges of solid solutions based on the terminal compounds and an intermediate range of demixing. The solid solutions are of tetradymite type (rhombohedral R 3 m). Their limits are related to the substitution of the selenium-tellurium and bismuth-indium atoms in the layers. Electrical conductivity and thermoelectric power measurements confirm the boundaries of the solid solution regions deduced from the thermal and X-ray diffraction data.

Redetermination of the phase equilibria in the system Tl2Te-Ag2Te

Abstract The Tl 2 Te-Ag 2 Te system phase equilibria have been redetermined by DTA, X-ray diffraction and the measurement of thermoelectric power. The existence of the phase Tl 2 Te was first established and its crystallographic parameters were determined. At least four compounds are formed in the system. The crystallographic parameters of the congruently melting AgTlTe (483°C) and the incongruently melting AgTl 3 Te 2 (382°C), Ag 8 Tl 2 Te 5 (440°C) Ag 5 TlTe 3 (446°C) and Ag 9 TlTe 5 (504°C) were determined. The 0–50 mol% Ag 2 Te range of the system is non-quasi-binary and a narrow solid solution range around the AgTITe composition gives a new insight into its dimorphic transformation.

Epitaxial growth of thin films of V2VI3 semiconductors

Epitaxial growth conditions of V2VI3 semiconductors have been studied using the molecular beam epitaxy technique, which was applied to the growth of Sb2Te3 on Bi2Te3 substrates. These substrates were prepared by gradient freeze method in a Bridgman apparatus. Ingots were cleaved along the (0001) plane. The deposition conditions have been studied as a function of two parameters: substrate temperature and flux ratios of the two elements. The quality of these epilayers was controlled by SEM and X-ray diffraction. Epilayers of good quality have been obtained for the first time.

Trois phases du ternaire CuTlS

Abstract Ternary compounds CuTlS 2 , CuTlS and Cu 2 Tl 0,5 S 2 have been prepared and caracterized by their crystallographic parameters. Meanwhile the first one is semiconductor, the other two have a metallic behaviour between 77°K and 300°K.

Crystallization kinetics of bulk amorphous (Se65Te35)100?x Sb x

Kinetic studies of crystallization in (Se65Te35)100−xSbx with 0⩽x⩽10 glasses, using the differential scanning calorimetry technique, were performed. Crystallization enthalpy data, ΔHc, were collected as a function of composition. The crystallization data were examined in terms of recent analyses developed for non-isothermal crystallization studies, to arrive at Ec. The results indicate bulk nucleation and crystallization with two- and three-dimensional growth, respectively, for the (Se65Te35)98Sb2 and (Se65Te35)92Sb8 glass composition.

The ternary system silver-antimony-tellurium. Study of the subternary Sb2Te3-Ag2Te-Te

Abstract The Sb 2 Te 3 -Ag 2 Te-Te subternary system was investigated using thermal analysis, differential scanning calorimetry metallographic technics and X-ray powder analysis. Three isopleth sections were constructed. The transitory reactions were characterized and the eutectic point coordinates were determined. Analysis of polythermal projection of this system is given.