Electrical Properties of Nonstoichiometric Uranium Dioxide

Abstract

Electrical conductivity and thermoelectric power measurements have been made on nonstoichiometric UO₂ at temperatures of 500–1150°C. The conductivity data in the single phase UO_2+x region can be represented by the equation $$\mathrm{\sigma (}\mathrm{ohm\; cm}{)}^{\text{−1}}{\text{=(3.8×10}}^6\text{)/T(2x)(1−2x)\hspace{0.17em}}\exp \text{[(−0.30±0.03\hspace{0.17em}}\mathrm{ev}\mathrm{)/kT].}$$ An approximate equation for the thermoelectric power Q, is $$\mathrm{Q=(k/e)\hspace{0.17em}}\ln \text{(1−2x/2x).}$$ The electrical measurements confirm the ionic theory of nonstoichiometry in UO₂, postulated on the basis of thermodynamic evidence. Nonstoichiometric UO₂ is a relatively simple ionic solid in which activated electronic hole transfer occurs between U⁵⁺ and U⁴⁺ ions in the lattice.