Semiconducting and Thermoelectric Properties of Sintered Iron Disilicide

The electrical resistivity, thermoelectric power, and Hall coefficient of sintered iron disilicide, Fe1−xMnxxSi2, and Fe1−yCoySi2 are measured over the temperature range from 77 to 1400 K. Regardless of the purity of raw materials, Fe1−xMnxSi2 and Fe1−yCoySi2 show semiconducting properties below the semiconductor-to-metal transition temperature Tc. Min and Co atoms in iron disilicide act as acceptor and donor, respectively. The energy gap of FeSi2 at 0 K is 1.00 eV, deduced from the temperature dependence of the Hall coefficient in the intrinsic region. The energy gap of Mn-doped FeSi2 decreases from 0.95 to 0.83 eV with increasing Mn amount. Above 150 K the lg ϱ versus 1/T dependence of Mn-doped FeSi2, exhibits an S-like decaying curve. This cannot be explained completely by ordinary band conduction, but can be done by small polaron conduction with crystalline distortions.