The electrical conductivity of nearly stoichiometric single‐crystal and polycrystalline uranium dioxide was measured from room temperature to 3000°K. Below approximately 550°K, the curve of log σ versus T−1 is linear with a calculated activation energy of approximately 0.17 ev. Between 550° and 1250°K, however, the shape of the curve changes; this change varies from one specimen to another. The electrical conductivity increases rapidly with increasing temperature above 1250°K with a change from p‐type to n‐type conduction. The best linear fit of the log σ versus T−1 curve above 1400°K is σ= 3.57 × 103e−(1.15 ev/KT). Above 1900°K, the curve deviates slightly from linearity and is best fit by the equation σ= 2.10 × 10−2T1.4e−(0.916 ev/KT).

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The thermal conductivities of sintered Al2O3 and UO2 were measured in the ranges 400° to 1700°C and 300° to 2100°C respectively. The conductivity values for Al2O3 agreed with those reported previously at all temperatures investigated. The conductivity of UO, decreased with increasing temperature to a minimum of 0.0050 cal per cm sec °C at about 1400°C, and then increased with increasing temperature to 0.0105 cal per cm sec °C at 2100°C.

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