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|Title:||Synthesis and Crystal Structure Characterisation of Sodium Neptunate Compounds|
|Authors:||SMITH A.l.; RAISON Philippe; KONINGS Rudy|
|Citation:||JOURNAL OF NUCLEAR MATERIALS vol. 413 no. 2 p. 114 - 121|
|Publisher:||ELSEVIER SCIENCE BV|
|Type:||Articles in periodicals and books|
|Abstract:||The present work reports a study of the chemical reactions between neptunium dioxide and sodium oxide leading to compounds with hexavalent neptunium. Solid state synthesis with different NpO2/Na2O ratios lead to the following polycrystalline compounds: Na2Np2O7 monoclinic (P1211), a-Na2NpO4 orthorhombic (Pbam), ß-Na2NpO4 orthorhombic, (Pbca) and ß-Na4NpO5 tetragonal (I4/mmm). Rietveld analysis of X-ray diffraction data allowed us to review the Np-Na-O system. Evolution of the cell parameters of a-Na2NpO4 was also followed as a function of temperature up to 1273 K by X-ray diffraction. The corresponding linear thermal expansion coefficients along the different axis were determined: aa = 41.3 10-6 K-1, ab = 35.0 10-6 K-1 ac ~ 0 K-1. From the high temperature X-ray diffraction experiment it was also possible to evidence formation of new phases at different temperatures.|
|JRC Directorate:||Nuclear Safety and Security|
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