Electrical Properties and Defect Structure of ThO2

The electrical conductivity and thermoelectric power of highpurity polycrystalline ThO₂ in thermodynamic equilibrium with the gas phase were measured as a function of temperature from 1000° to 1600°C and as a function of oxygen partial pressure from 1 to 10^?22 atm. An n -type electronic contribution to the conductivity is observed above 1400°C at low oxygen pressures. An analytic solution is presented for the oxygen pressure dependence of the total conductivity in the mixed ionicelectron hole conduction region observed at higher oxygen pressures. The activation energies for p -type and ionic conduction are 1.0 and 0.9 eV, respectively. The combined conductivity and thermal emf data give a lower limit of ～6 cm²/V-s for the electron hole mobility.