MIXED OXIDE SYSTEMS OF LANTHANIDE AND ACTINIDE ELEMENTS. II. ROENTGEN STUDY OF THE SYSTEM PLUTONIUM OXIDE-EUROPIUM OXIDE

S>The lattice parameters of mixed oxide samples of known plutonium and europium contents were determined to a high precision. In the plutonium oxide/ europium oxide system a fluorite phase appears in the range 0-42 mo1e% EuO/sub 1,5/. From 0-- 15 mole% EuO/sub 1,5/, the lattice parameter of PuO/sub 2/ is scarcely affected, while further additions of Eu/sub 2/O/sub 3/, in the range 15-- 42 mole% EuO/sub 1,5/ cause the parameter to increase. This kink in the parameter/composition plot is interpreted in terms of an oxidation of plutonium to a valency >4, enforced by the incorporation of Eu/sup 3+/ in the fluorite lattice. With europium contents above 42 mole% EuO/sub 1,5/ a fluorite phase with considerable lattice distortion appears, while above 60 mo1e% EuO/sub 1,5/ the transition to the C-type of Eu/sub 2/O/sub 3/ is found. (auth)