Electrical Transport in Ionic Crystals

Abstract

Electrical conduction in solids is caused by the directed movement of electrons, holes or ions under the action of electric fields applied from outside. The electrical conductivity σ is equal to Σi ni q1 µi for a solid obeying Ohm’s law. Here, ni is the number per unit volume of the mobile charge carriers of the 1th type, q. the charge on each such carrier and µi the mobility. There is no transport of matter when electrical conduction is by electrons or holes as in metals and semi conductors. Such a conduction can be recognised by Hall effect measurements. On the other hand, in ionic conduction, charge transport is accompanied by mass transport. Crystals like KCl are appropriately called solid electrolytes. Hall effect, is too small to be observed in this case. However, when a d.c. current is passed for a sufficiently long time through three plates of the crystal in series, the end plates should show a change of mass if the conduction is by the movement of the ions. In fact, it should be possible to deduce the transport numbers of ions. If the measurements are sufficiently accurate1–7. Even otherwise, qualitative information can be obtained as to the more mobile carriers.