Phenomenological Description of Continuous Electronic Transitions

Abstract

Many electronic transitions in metals occur at some fixed pressure at a given temperature and are accompanied by a volume discontinuity. On the other hand, some electronic transitions, including those in compounds of iron involving changes in spin state or oxidation state, occur continuously over a range of pressure. In fact, for the reduction of ferric to ferrous iron, one can frequently represent the conversion over a considerable range of pressure by the relationship:

$$K=\frac{{{C}_{II}}}{{{C}_{III}}}=A{{P}^{M}}$$

(4.1)

where C _II and C_III are the fractions of ferrous and ferric ions, p is the pressure and A and M are constants. For some transformations the conversion at first increases with pressure and then levels or may actually go through a maximum.