The diffusion of 45Ca was measured in single crystals of CaF2 and CaF2-0.34mol%YF3 by using a precision sectioning technique. In pure CaF2, at temperatures of between 800 and 1300C, the data could be described by:

D (cm2/s) = 4.8 x 107 exp[-5.160(eV)/kT]

The effect of YF3 was to increase the diffusivity at temperatures below 950C, but the amount of the increase was much smaller than that expected for a vacancy mechanism; unless a binding energy, between Y3+ ions and cation vacancies, of more than 0.6eV was assumed.

A.D.King, J.Moerman: Physica Status Solidi A, 1974, 22[2], 455-63