13.8 - Haeffner effect, electromigration, and thermal transport

Summary

Isotope effects are known to exist in liquid metals from a variety of experiments; in particular, those using the light isotopes Li⁶ and Li⁷. Some striking—and surprising—regularities exist more generally, especially the effect discovered by Haeffner (1953). Here, in an applied electric field, the light isotope in the isotopic liquid metal mixture is found, invariably, to move toward the anode. No known exceptions to this rule exist. The problem of electromigration is closely related, but presumably the understanding of the Haeffner effect is an essential prerequisite to an understanding of this phenomenon. For a review of electromigration, the article by Huntington (1973; see also Jones, 1980) may be consulted.

The facts, and some basic phenomenology, have been presented by Ginoza and March (1985) for (1) the Haeffner effect just discussed, (2) self- and mutual diffusion, and (3) shear viscosity.

Here, the aim is to present the theory underlying the Haeffner effect, in lowest-order Born approximation, in a form that is directly related to electrical resistivity. Some attempts to transcend this approximation will then be briefly discussed.

Haeffner effect

As mentioned already, it is useful to regard the Haeffner effect as a special case of the more general electromigration problem in liquid metal alloys. This is the effect found in a number of binary systems, where the constituentions drift in opposite directions under the influence of an applied dc electric field (see also Tyrrell and Harris, 1984).