Measurements were made of the electrical conductivity of single crystals which contained 0.02 to 0.15mol%Ca. It was deduced that the activation energy for the formation of Schottky defects was 46kcal/mol, and that the activation energy for the migration of F ion vacancies was 7.6kcal/mol.

W.L.Fielder: NASA Report TN D-5505, 1969