The ionic conductivity of pure, yttrium-doped, and sodium-doped cadmium fluoride has been determined from room temperature up to a maximum temperature of 500°C. Results show the mobile defect to be fluorine vacancies with an activation energy of motion of 0.44 eV. A mechanism is developed for the conversion of yttrium-doped CdF2 to a semiconductor based on vacancy motion. An anomalous conductivity curve is observed in crystals containing sodium impurity. Possible explanations for this are discussed in terms of association effects.

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