We note in Section 12.5 (Figure 12.20) that in FeO

Chapter 18, Problem 18.47

(choose chapter or problem)

We note in Section 12.5 (Figure 12.20) that in FeO (wstite), the iron ions can exist in both Fe2 and Fe3 states. The number of each of these ion types depends on temperature and the ambient oxygen pressure. Furthermore, we also note that in order to retain electroneutrality, one Fe2 vacancy is created for every two Fe3 ions that are formed; consequently, in order to reflect the existence of these vacancies, the formula for wstite is often represented as Fe(1x)O, where x is some small fraction less than unity. In this nonstoichiometric Fe(1x)O material, conduction is electronic and, in fact, it behaves as a p-type semiconductorthat is, the Fe3 ions act as electron acceptors, and it is relatively easy to excite an electron from the valence band into an Fe3 acceptor state with the formation of a hole. Determine the electrical conductivity of a specimen of wstite with a hole mobility of 1.0 105 m2 /V#s, and for which the value of x is 0.040. Assume that the acceptor states are saturated (i.e., one hole exists for every Fe3 ion). Wstite has the sodium chloride crystal structure with a unit cell edge length of 0.437 nm. 1