STRUCTURAL FORMULA OF URANINITE

A revised structural formula for uraninite, nominally UO2, is presented: (U1-x-y-z4+U(x)6+REE(y)3+M(z)2+)O2+x-(0.5y)-z, which emphasizes the role of cationic substitutions. This formula clarifies the relationship between structural properties (e.g., unit cell parameters), oxidation state (U6+/U4+ ratio), and phase transformations with increasing concentrations of excess oxygen. The formula demonstrates that the amount of excess oxygen required to compensate for increased positive charge due to U6+ is less than suggested by the amount of U6+ alone. This may increase the stability field of uraninite under oxidizing conditions relative to synthetic UO2+x.