3 Uranium oxide UO2 tends to possess a wide range of nonstoi

3. Uranium oxide (UO2) tends to possess a wide range of non-stoichiometric compositions when exposed to reducing and oxidizing conditions, wherein some of the U4+ ions become U3+ and US+, respectively. (a) Write the two separate Kroger-Vink defect reaction equations that describes both of these non-stoichiometri c materials. (b) Write the chemical formulas (e.g. AxBl-x) that one would use to describe the compositions of these two different non-stoichiometric compounds.

Solution

(a) for reduction (U⁺³) it will create an anion vacancy in the lattice. the reaction can be written as

U_(s) <=> U^x_u + V^.._o + 2e^\'

for oxidation cation is in deficiency on the lattice (U⁺⁵)

1/2 O_{2 (g)} <=> V^\'\'_u + O^o_o + 2h^.

(b) for U⁺³, UO_1-x and for U⁺⁵, U_1-xO