Synthesis and Crystal Structure Characterisation of Sodium Neptunate Compounds

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.

SMITH A.L.;  RAISON Philippe;  KONINGS Rudy; 

2011-07-06

ELSEVIER SCIENCE BV

JRC60780

0022-3115,   

http://www.elsevier.com/locate/jnucmat,    https://publications.jrc.ec.europa.eu/repository/handle/JRC60780,   

10.1016/j.jnucmat.2011.04.009,