For the first time combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) experiments were carried out to probe the short- and long-range order in lanthanum-modified PbTiO3 ceramic materials (Pb1 - x La x TiO3) for x ranging from 0 to 30 atom % of La. XRD results show that a tetragonal structure fitted well to all samples, except to the one with 30 atom % of La for which XRD results highlighted a cubic unit cell. XRD refinements also confirmed the existence of only A-site vacancies. X-ray absorption near edge spectroscopy (XANES) measurements indicate that the local structure around Ti atoms has a different compositional dependence from the one obtained from XRD, mainly for the sample with 30 atom % of La. According to XANES data, for the sample with 30 atom % of La, a local distortion around Ti atoms persist. The analysis of extended X-ray absorption fine structure (EXAFS) spectra shows a decrease in the local disorder around Ti atoms as the content of La increases. Structural details, in terms of short and long-range order, are presented and the correlation between the XRD and XANES/EXAFS data is discussed.

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Electrochemistry / Electropolymerization / Organic media / Uranium / Neptunium / a Spectrometry sources / Polyacrylonitrile SummaryThe electrochemical reduction of uranium and neptunium ions is achieved in aprotic solvents in presence of acrylonitrile. The cathodic deposit on a usual metal consists of a grafted polyacrylonitrile layer in which actinide oxide or actinide metal has been inserted as a consequence of the overall cathodic reaction. As polyacrylonitrile is an insulating material, the electrochemical polymerization reaction is stopped when the polymer layer thickness reaches 1000 A at maximum.The material we thus produced may be used as an alpha spectroscopy source and we report here the results originating from the preparation of more than hundred samples. -ECI V) Fig. 1. Voltammetric two-step reduction of acrylonitrile (0.1 M) in AN with Et 4 NC10 4 , 0.05 M; Ni electrode, total surface: 2 cm 2 ; υ = 50 mV s" 1 .

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We demonstrate in this paper that the electrochemical Tafel-plots method gives a good account for the understanding of the overall mechanisms of reactions occurring in concentrated solutions. The Tafel-plots method is capable of predicting the results of long time electrolysis such as preparation of metallic thorium in the (Li-K)Cl eutectic from Th 4+ ion and preparation of trivalent uranium from U 4+ ion in DMF at room temperature.The values of the transfer coefficient gained by the Tafelplots method are compared with the same values deduced from sampled polarography in dilute solutions.In all cases, the mechanisms of the various electrode reactions are made clear while comparing the experimental Tafel slopes with theoretical values calculated from models for different paths of reaction.

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