MECHANISM OF ELECTRICAL CONDUCTION IN BETA-FESI2

Electrical conductivity, thermoelectric power and Hall coefficient of β‐FeSi2 doped with cobalt (n‐type) or aluminium (p‐type) are measured between 100 and 1200 °K. The conductivity of n‐FeSi2 follows an exponential dependence on temperature. The temperature dependence of the thermoelectric power cannot be interpreted on the basis of conduction in a band. With the assumption that conduction in n‐FeSi2 is caused by small polarons, the mobility at room temperature is found to be μn = 0.26 cm2/Vs. The activation energy of the mobility is 0.06 eV, the density of states N = 1.2 × 1022 cm−3. The electrical properties of p‐FeSi2 can be interpreted using the band model with a hole mobility μp ≈ 2 cm2/Vs, which varies as T−1/2 in the region of extrinsic conduction. From intrinsic conduction a band gap of 0.9 to 1.0 eV is deduced. The disappearance of the thermoelectric power at high temperature is related to the semiconductor‐to‐metal transition at 1200 °K. Copyright © 1968 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim