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Joubert J.-M.,CNRS East Paris Institute of Chemistry and Materials Science
International Journal of Hydrogen Energy | Year: 2010

A new equation of state for hydrogen gas (0 ≤ P ≤ 1011 Pa, 298 ≤ T ≤ 1000 K) has been derived and is given in an analytical form. It is compatible with the Calphad approach (i.e. it is an analytical equation of the Gibbs energy as a function of pressure). This equation has been applied to the Calphad assessment of the H-Rh system, an example of system forming a metal hydride only at a very high pressure. A set of self-consistent thermodynamic parameters describing the Gibbs energy of each phase has been obtained. The scarce experimental data available for this system, particularly the high formation pressure of the hydride, have been well reproduced which otherwise would have been impossible without considering the non-ideal behaviour of the gas phase. © 2010 Professor T. Nejat Veziroglu.

Wildman E.J.,University of Aberdeen | Skakle J.M.S.,University of Aberdeen | Emery N.,CNRS East Paris Institute of Chemistry and Materials Science | McLaughlin A.C.,University of Aberdeen
Journal of the American Chemical Society | Year: 2012

Colossal magnetoresistance is a rare phenomenon in which the electronic resistivity of a material can be decreased by orders of magnitude upon application of a magnetic field. Such an effect could be the basis of the next generation of memory devices. Here we report CMR in the antiferromagnetic oxypnictide NdMnAsO 1-xF x as a result of competition between an antiferromagnetic insulating phase and a paramagnetic semiconductor upon application of a magnetic field. Mn 2+ oxypnictides are relatively unexplored, and tailored synthesis of novel compounds could result in an array of materials for further investigation and optimization. © 2012 American Chemical Society.

Champion Y.,CNRS East Paris Institute of Chemistry and Materials Science
Materials Science and Engineering A | Year: 2013

Low temperature (77K, 243K and 255K) mechanical tests were carried out at strain rates between 7.10 -4s -1 and 5.10 -2s -1 on pure ultrafine grained (UFG) copper (grain size 100nm) to mimick room temperature high strain rates. Variation of the activation volume measured as a function of the stress is consistent with the analytical model proposed in [C. Duhamel, Y. Bréchet, Y. Champion Int. J. Plast. 26 (2010) 747-757] to explain the rheology of UFG metals. This model is based on dislocations interactions at grain boundaries and grain boundaries sliding. The experiments confirm that the strain rate sensitivity (which should be a criterion for plasticity in absence of macroscopic work hardening) increases with the strain rate (or stress) at high strain rate, as also observed for nanotwinned copper. From the model, a strain rate sensitivity criterion is derived, function of a characteristic UFG strength parameter and grain boundary properties. The analytical description of deformation of UFG including microstructural properties should help for a quantitative control of the macroscopic properties of UFG. © 2012 Elsevier B.V.

Goncalves A.P.,University of Lisbon | Godart C.,CNRS East Paris Institute of Chemistry and Materials Science
European Physical Journal B | Year: 2014

The need of alternative "green" energy sources has recently renewed the interest in thermoelectric (TE) materials, which can directly convert heat to electricity or, conversely, electric current to cooling. The thermoelectric performance of a material can be estimated by the so-called figure of merit, zT = σ α 2 T/λ (α the Seebeck coefficient, σ α 2 the power factor, σ and λ the electrical and thermal conductivity, respectively), that depends only on the material. In the middle 1990s the "phonon glass and electron crystal" concept was developed, which, together with a better understanding of the parameters that affect zT and the use of new synthesis methods and characterization techniques, has led to the discovery of improved bulk thermoelectric materials that start being implemented in applications. During last decades, special focus has been made on skutterudites, clathrates, half-Heusler alloys, Si1-x Ge x-, Bi2Te 3- and PbTe-based materials. However, many other materials, in particular based on intermetallics, pnictides, chalcogenides, oxides, etc. are now emerging as potential advanced bulk thermoelectrics. Herein we discuss the current understanding in this field, with special emphasis on the strategies to reduce the lattice part of the thermal conductivity and maximize the power factor, and review those new potential thermoelectric bulk materials, in particular based on intermetallics, pnictides and chalcogenides. A final chapter, discussing different shaping techniques leading to bulk materials (eventually from nanostructured TE materials), is also included. © 2014 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

Joubert J.-M.,CNRS East Paris Institute of Chemistry and Materials Science
JOM | Year: 2012

A review of the metal-hydrogen systems modeled or investigated with the CALPHAD method is presented. The specific features of metal-hydrogen systems in relation with the CALPHAD modeling are detailed, and the problems and needs related to the description of such systems are highlighted. © 2012 TMS.

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