Different mechanisms can drive a metal-based alloy to become a semiconductor.
Among the transition metal base alloys, the most studied to date are the intermetallic phases of the Heusler and semi-Heusler types. These alloys are rich in compositions and are found to exhibit semiconducting gap, half-metal ferromagnet, and strongly enhanced effective mass properties. Several alloys have shown promise as prospective thermoelectric materials. The unusual electronic and thermoelectric properties of these systems will be discussed.