EFFECT OF CATIONS ON LATTICE-CONSTANTS OF (MYU1-Y)O-2.00 (M=PU, TH, LA) AT LOW DOPED CATION CONCENTRATIONS

In order to clarify the effect of doped cations on the lattice constan ts of stoichiometric (MyU1-y)O-2.00 (M=Pu, Th, La) solid solutions at small y, the lattice constants of stoichiometric (MyU1-y)O-2.00 as a f unction of doped cation concentration were measured at room temperatur e by the powder X-ray diffraction method. The lattice constant of stoi chiometric uranium dioxide doped with plutonium ions decreased linearl y with increasing plutonium concentration up to 20 at%, whereas the la ttice constants of the dioxide doped with thorium and lanthanum ions i ncreased linearly with increasing thorium and lanthanum concentration up to 4 and 9 at%, respectively. No abnormal behavior was observed at y=0.04 for stoichiometric (PuyU1-y)O-2.00 and at y=0.02 for stoichiome tric (ThyU1-y)O-2.00 as reported in the literature. The valence of the doped cations is discussed in terms of the dependence of the cation c oncentration on the lattice constants by assuming a random distributio n of doped cations in uranium dioxide and an ionic model where every c ation and anion form a rigid sphere. (C) 1998 Elsevier Science S.A.