ELECTRICAL RESISTIVITIES OF NONSTOICHIOMETRIC CERIUM HYDRIDE SINGLE CRYSTALS

Electrical resistivities as a function of temperature (-30° to 25°C) were determined on single crystals of cerium hydride ranging in composition from CeH1.94-CeH2.85. Measurements were performed in an inert-atmosphere dry box using the four-point probe technique. Cerium hydride exhibited metallic behavior in the range CeH1.9- CeH2.7. However, at a composition of about CeH2.35, a positive temperature coefficient of conductivity indicative of semiconductivity was observed. It is proposed that the semiconductivity of cerium trihydride is due to hydrogen vacancies which act as electron donors in the CeHt structure. The observed change in slope of the resistivity vs l/T curves yielding two apparent activation energies is caused by the presence of substitutional oxygen impurities which act as electron acceptors. On the basis of this model, the donor level is calculated to be 0.30 eV below the conduction band.