Étude du système BaF 2NpF 3 par diffraction X et spectroscopie Mössbauer ( 237Np)

Abstract

The BaF 2-NpF 3 system has been studied using X-ray diffraction and Mössbauer ( 237Np) spectroscopy. The system was studied at 973 K, either by reaction of BaF 2 and NpF 3 in an atmosphere of fluorhydric acid and argon or by reaction of the fluorides in stoichiometric proportions in a platinum tube put in a nickel microbomb. Two solid solutions were observed, firstly a fluorite solid solution (formula Ba 1 − x Np III x F 2 + x with 0 < x ⩽ 0.25) and secondly a hexagonal (type LaF 3) solid solution (formula Ba 0.05 + x Np III 0.95 − 2 x Np IV x F 2.95 (0 ⩽ x ⩽ 0.475)). Mössbauer spectroscopy ( 237Np) and X-ray diffraction enabled a new hypothesis to be put forward of a substitution mechanism by which trivalent neptunium is replaced by barium in this solid solution.