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Doped ceria is known for its high ionic conductivity which is limited by the creation of defect clusters. We investigate using Molecular Dynamics the evolution of the structure and oxygen diffusivity of the Ce 0.9 M 0.1 O 1.95 (M = Gd, Sm) doped and co-doped CeO 2 systems. Two configurations concerning the introduction of the doping ions and oxygen vacancies inside the structure are generated and compared, the random one (R) and the neighbor one (N). The pair potential parameter set is chosen among three sets by comparison with experimental data. The pair correlation function first peak is fitted by a lognormal function to take into account the asymmetry. The evolution of the coefficient of thermal expansion, the coordination number and the bond lengths of the different ion pairs with the temperature, is presented. The influence of the local C-type sesquioxide M 2 O 3 structure on those parameters is discussed. No significant positive co-doping effect on the oxygen diffusion process is revealed. The random configuration of the defects leads to the highest oxygen diffusivity and to the lower activation energy whatever the doping ion (Gd, Sm or Gd/Sm). [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a direct measurement method for optical properties of different materials at cryogenic temperatures from 20K to 200K. It has been developed within the framework of the design of Planck program. Planck is a satellite of the European Space Agency (ESA) that will be launched in 2008. The scientific goal of the Planck mission is to make observations of the temperature anisotropy and polarisation of the Cosmic Microwave Background. The equivalent temperature of the observed radiation is about 3K and the telescope baffle temperature should not exceed 60K in order to work properly. The large Planck telescope is passively cooled by radiating to the Deep Space, so that a good knowledge of the thermo-optical properties of its coating is of utmost importance for thermal modelling. However, up to now, few measurements have been done at such low temperatures. We derived a direct measurement method for the total directional emissivity of various coatings of interest for satellites applications. The effective spectral range chosen the measurements covers 6–800μm. We will describe the design of the measurement apparatus and present results for several coatings. [Copyright &y& Elsevier]