The conductivity and thermoelectric power of homogeneous crystalline specimens of thorium oxide are being measured in different gas atmospheres and in vacuum. Conduction in hydrogen is relatively stable and is accompanied by electrolytic discoloration. In oxygen, conductivity is higher, increases markedly with flow of current and is not accompanied by visibly electrolytic deposits.
In all cases where a change is made from an oxygen atmosphere to a non-oxygen atmosphere (or vacuum) the conductivity decreases. One therefore speculates that the material is a p-type conductor when in oxygen and in the temperature range concerned (700°-1000 ° C.) This is corroborated by the polarity of the Seebeck effect. In vacuum at higher temperatures evidence points to n-type conduction.
Data regarding the variation of thermoelectric power with temperature in an oxygen atmosphere yield energy-gap values in fair agreement with those obtained from electrical conductivity. Using the simplest semi-conductor theory with present data the calculated density of impurity centers is unreasonably high. However, it is to be expected that, under the circumstances, the impurity density will vary with temperature. An attempt to take this into account mathematically is in progress.