Abstract
The diffusion of Pb++ ions in single crystal KCl has been studied over the temperature range, 200°—475°C. A radioactive tracer technique has been used in two types of measurements: diffusion from a deposited surface layer of PbCl2 and diffusion from PbCl2 vapor. For treating the data from the vapor diffusion experiments, a graphical method has been developed which enables D to be obtained as a function of Pb concentration. The diffusion of Pb in pure KCl obeys the equation D=1.02×10—3 exp (—23 300/RT)/cm2 sec. The behavior of D as a function of concentration supports the Lidiard theory of diffusion by impurity-vacancy complexes. An association free energy for complex formation of 0.49±0.1 eV has been estimated from the data. This is in agreement with the trend shown in theoretically calculated values for other impurities in KCl. An anomalous rate of diffusion has been observed for Pb near the surface of some PbCl2-doped KCl crystals.
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