SURFACE AND BULK ELECTRICAL-PROPERTIES OF THE HEMATITE PHASE FE2O3

Electrical properties of Fe2O3 were studied by using several electrical methods such as electrical conductivity, thermopower (Seebeck effect) and work function. The studies were performed at elevated temperatures (1053-1153 K) and under controlled oxygen activity (10(2)-10(5) Pa). Samples of different thickness varying between 10(3) nm and 1 mm were taken for the measurements of both electrical conductivity and thermopower. It has been found that the exponent of the p(O2) dependence resulting from the work function measurements (1/n-phi) is about 1/2. Both thermopower and electrical conductivity data are well consistent with work function data for the thin film (1000 nm) of Fe2O3. The charge transport in Fe2O3 has been interpreted in terms of small polaron mechanism. Analysis of measured electrical parameters, regarding the thickness of studied specimens, indicates that the near-surface layer of Fe2O3 exhibits much higher deviation from stoichiometry than the bulk phase and resulting strong interaction between charge carriers. This effect has been interpreted in terms of segregation of intrinsic lattice defects to the surface, and presumably also to grain boundaries, of Fe2O3.