Calcium diffusion in pure and YF3-doped single crystal CaF2

The diffusion of 45Ca has been measured in single crystals of CaF2 and CaF2 + 0.34 mol % YF3 using a precision sectioning technique. In pure CaF2 between 800 and 1300 °C, D = = 4.8×107 exp (—5.160 eV/kT) cm2/s. The effect of YF3 is to increase D at temperatures below 950 °C but the magnitude of the increase is much smaller than expected for a vacancy mechanism unless a binding energy between Y3+ ions and cation vacancies of >0.6 eV is assumed. It is shown that the results may correspond to diffusion via cation–anion vacancy pairs at all temperatures investigated.