Tellurium System Research Articles

Donors for Organic Metals: Molecular Aspects

AbstractPhysicochemical issues are discussed which are relevant to chemists interested in the synthesis of unknown compounds to serve as precursors to organic metals. Molecular topics are emphasized, physical and structural concepts which motivate synthetic activity in chalogen chemistry are presented, and new results in selenium and tellurium systems are summarized. Two model representations for donor molecular structures based on polyenes and polyacenes are presented and known examples are discussed. Quantitative correlations between gas phase vertical ionization potential and solution electrochemical redox potential are examined using donors of interest for organic metals as data. Limitations of such correlations and consequences of these shortcomings are given. Finally, possible future directions for several of these topics are posed.

Pressure - temperature relations in the silver - tellurium system at 75 at-% tellurium

The p,T-relations in the silver-tellurium system at 75 at-% Te were studied by high pressure DTA and quenching experiments at pressures up to 3.2 GPa. Fitted data for the phase boundaries are given. AgTe 3 becomes a stable phase in the system above 0.4 GPa. In quenching melts with a nominal composition AgTe 3 from high temperatures, stable and metastable equilibria can be observed. Conditions for the formation of homogeneous AgTe 3 from the melts in the low-pressure region are discussed.

Etude du systeme PbTeTl 2Te. Mise en evidence des phases derivées de Tl 5Te 3

Thallium-lead tellurium system has been investigated by thermal analysis an X-Ray diffraction methods. The cross-section PbTe-Tl 2Te seems to be a quasibinary one. An intermediate phase of stoechiometry Tl 4PbTe 3 has been evidenced. This phase, which decomposes peritectically at 594°C, and his stannous homologous, have been studied by comparison with Tl 5Te 3.

Crystallization of silicon from the silicon-chalcogen vapor phase

With the target of preparing homogeneous chalcogen-doped silicon crystals, conditions and features of vapor phase growth have been investigated. Consequent evaluation of this work, for the first time, demonstrated how to grow S-doped crystals in such manner, and principally, enabled us to guide transport reactions via the pure sulphur, selenium, and tellurium system, respectively, in order to obtain large and highly perfect crystal areas. Optimization of the “sandwich method” which is known from the literature as a close-spaced system allowed us to realize epitaxial growth layers of thicknesses up to 10 mm based on diameters of 30 mm maximum.

Electrical and optical properties of binary glasses from the arsenictelluriumselenium system

An investigation of binary glasses derived from the arsenicseleniumtellurium system is described in which measurements were made of d.c. conductivity over a range of temperatures, space charge limited current, density and absorption in the near infrared region. For the higher temperature region the electrical results were consistent with conduction being due to carriers excited into extended states. While conduction at lower temperatures may in some cases be due to carriers hopping in localized states at the band edges, an alternative approach in which the localized states were considered to act as donors and acceptors gave satisfactory agreement with the experimentally determined conductivity versus temperature and activation energy versus temperature relationships and with the value of the pre-exponental constant in the conductivity expression. An anomalous field dependence of conductivity was found for annealed specimens of two glasses and it is tentatively suggested that this is associated with the creation of an impurity band. Measurements of space charge limited current showed that gold gave ohmic contacts to the glass, whereas silver and copper did not. The measurements also provided evidence for the localized states having an exponential distribution. Changes of electrical properties and density as a function of glass composition are discussed in the light of possible structural changes taking place in the glasses. The absorption edges of the glasses in the infrared region were found to be exponential in form and had slopes that did not very greatly for the range of compositions studied.

The Enthalpies of Binary Mixtures of Chalcogen Elements

Abstract The enthalpies of binary mixtures among chalcogen elements were measured by means of calorimetry. In the system of sulfur+selenium, the positive enthalpy increment suggests the formation of a co-ring and a co-chain on mixing. In the selenium+tellurium and sulfur+tellurium systems, some local ordered structures were deduced from the minimum points of the enthalpy at the compositions of Te3Se2 and Te3S. In the latter system, the entropy of mixing was calculated from the reported phase diagram and the present enthalpy values. The entropy diagram also suggests that the local order is present.

Mass transport studies in nickel—liquid tellurium system

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