Activation energies for the motion of interstitial F- ions in pure and doped samples were deduced from the temperature dependence of the ionic conductivity. The results showed that the incorporation of Ho3+ ions into the CaF2 lattice increased the electrical conductivity. This was explained in terms of the formation of additional interstitial F- ions which compensated the excess positive charge of the Ho3+ ions. The additional conductivity of the impure crystals was determined by the interstitial F- ions. The closeness of the activation energies (table 183) suggested that there was a complete dissociation of the rare-earth ion plus interstitial F- ion complex.

V.V.Popov: Fizika Tverdogo Tela, 1969, 11[7], 1982-4

Table 183

Activation Energy for the Migration of F in Doped CaF2 at 700 to 1100K