Pipe Diffusion in LiF

Impurity diffusion of Na ions along dislocations in LiF has been studied by both dc and transient techniques. The Na impurity is injected into the LiF by plating NaCl on one surface of the LiF and placing a potential across the crystal at an elevated temperature. Large-scale diffusion with Na dendrite formation is observable in a dc arrangement and the diffusion can be measured by either radioactive tracer methods or measurement of charge transport. Transient experiments yield an activation energy for diffusion of approximately 0.3 eV for both edge and screw dislocations, and D0=0.01 cm2/sec. Analysis of the charge effects in the core of the dislocations leads one to propose a very large vacancy density in the core, and the experiments are even best understood in terms of a hollow of atomic dimensions along the dislocation core.