DONOR LEVELS IN ALPHA-FE2O3

Recently one of the authors reported that a Schottky alpha -Fe//2O//3 diode responds to the change in the ambient partial pressure of oxygen even at room temperature after a large reverse bias voltage is applied to the diode. The sensing mechanism can be clarified by analyzing the impedance of the diode. In the impedance analysis of the diode, the capacitance and/or conductance associated with oxygen adsorption should be distinguished from that of bulk states. The present work estimates the energy level of donors in alpha -Fe//2O//3 by employing the admittance spectroscopic method. In sintered alpha -Fe//2O//3 the activation energy of 0. 164 eV was obtained from the temperature dependence of the electric conductivity in the range 77 to 300 K. It is concluded that in non-stoichiometric alpha -Fe//2O//3 the donors due to oxygen vacancies lie at 0. 078 eV below the bottom of the conduction band originating from 3d or 4s orbitals of iron atoms. 14 Refs.