The dielectric constants of UO2, UO2+x, and U4O9have been measured using the standing wave method at 9.1 GHz in the temperature range 233ndash;300 K. The conductivity is calculated from the imaginary part of the dielectric constant. The conduction mechanism is attributed to small polaron hopping, since the mobility is very small (1.2times;10minus;5cm2/Vthinsp;s forx=0.15 at 300 K). From the analysis of the dependence of the conductivity onxand the activation process, it is concluded that there are two types of charge carriers; free carriers at low concentrations (x=0.07, 0.10) and carriers bound to interstitial oxygen ions at high concentrations (x=0.15, 0.20).Ea=0.15plusmn;0.01 eV andJ=0.01plusmn;0.001 eV are obtained for free carriers andEa=0.25plusmn;0.01 eV andJ=0.08plusmn;0.005 eV for bound carriers. The dielectric relaxation time is estimated to be 2.7times;10minus;11s.
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