Effects of Gadolinium Doping on Electrical Properties of UO2 Grain Boundaries.

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<BR>Complex impedance measurements were made on Gd-doped UO2 to study Gd doping effects on electrical properties of the matrix and grain boundary. The Gd contents ranged from 0.5 to 10 wt% ; temperature from 295 to 1, 273 K ; and frequency from 5 to 4 × 107 Hz. <BR>The matrix conductivity increased almost linearly with Gd content, indicating that the number density of electron holes also increased almost linearly with increasing Gd. The grain boundary capacitance of the Gd-doped UO2 was larger than that of UO2 by about 3 orders of magnitude. The grain boundary conductivity of the Gd-doped UO2 was also larger than that of UO2, but decreased rapidly with increasing Gd content, between 0.5 to 10 wt %. The migration energy of electron holes across a grain boundary was larger than that in the matrix and seemed to increase with Gd content. <BR>It was presumed from these results that Gd ions segregated to the grain boundaries to form a potential barrier for the migration of electron holes. The barrier thickness was estimated to be a few nanometers from the grain boundary capacitance. The energy barrier estimated from the migration energy of electron holes seemed to increase with Gd content.
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