Effects of composition on lattice parameter of UO/sub 2+x/

A method is described for synthesizing cubic UO/sub 2+x/ (0.03 < x < 0.38). Synthetic UO/sub 2+x/ was chemically analyzed and examined by X-ray diffraction with an internal standard; the lattice parameter a0 was found to be linearly dependent on the composition throughout the range of existence of the phase: a0 = 5.4696 - 0.1495 x (0 < x < 0.38). The confidence range for this straight line is such that Vegard's rule is closely obeyed within the error of measurement. Specimens of UO/sub 2+x/ oxidize fairly rapidly in air at room temperature, which is due to the large specific surface (26.8-29.0 m2/g). The oxidation is accompanied by reduction in the lattice parameter and by the formation of an X-ray amorphous phase similar in composition to UO3. A similar oxidation mechanism appears to apply for natural uranium oxides. Therefore, this relationship can be used to determine a lower limit to the composition of a natural oxide from X-ray data