The electrical resistivity, Hall coefficient, and thermoelectric power have been measured over the temperature range from 4.2 to 800'K on Col Fe Si solid solutions, with x varying from 0 to 1. The specimens are n-type near x=0. In the purest specimen of CoSi the electron mobility reaches 800 cm'/volt-sec at 4.2'K. With increasing x, hole conduction becomes predominant. Anomalies are observed for intermediate compositions. The temperature range over which the Hall coefricient and the thermoelectric power take opposite signs is unusually wide compared with ordinary p-type semiconductors. Detailed analysis of the Hall coeiiicient and thermoelectric power based on a two-carrier model leads to the conclusions: (1) The upper and the lower bands overlap in energy for Co&,Fe,Si solid solutions. (2) By substitution of one iron atom for one cobalt atom in the solid solutions, approximately one hole is produced. For CoSi the best fit to the data is obtained with the overlap energy of 0.02 eV, with the electron effective mass of 2m0, with the hole effective mass of 4 m0 and with the electron-to-hole mobility ratio of 5. For the solid solutions, the observed data are qualitatively interpreted assuming that the overlap energy and the hole effective mass increase with x, but the mobility ratio and the electron effective mass remain unchanged. It is also suggested that interband scattering becomes predominant in passing from CoSi to FeSi.

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