THE INFLUENCE OF OXYGEN ON THE ELECTRICAL PROPERTIES OF CaF2 AND BaF2 SINGLE CRYSTALS A. HAMMOU, M. DUCLOT and V.A. LEVITSKII J. Phys. Colloques, 37 C7 (1976) C7-342-C7-348 DOI: 10.1051/jphyscol:1976779