Problem 18.47 noted that FeO (wustite) may behave as a
Problem 18.47 noted that FeO (wustite) may behave as a semiconductor by virtue of the transformation of Fe2+ to Fe3+ and the creation of Fe2+ vacancies; the maintenance of electro neutrality requires that for every two Fe3+ ions, one vacancy is formed. The existence of these vacancies is reflected in the chemical formula of this nonstoichiometric wustite as Fe(1 â x)O, where x is a small number having a value less than unity. The degree of nonstoichiometry (i.e., the value of x) may be varied by changing temperature and oxygen partial pressure. Compute the value of x that is required to produce an Fe(1 â x)O material having a p-type electrical conductivity of 2000 (ohm-m)-1; assume that the hole mobility is 1.0 x 10-5 m2/V-s, the crystal structure for FeO is sodium chloride (with a unit cell edge length of 0.437 nm), and that the acceptor states are saturated.
