Thermoelectric Properties of Boron-Rich Solids and their Possibilities of Technical Application

The thermoelectric properties of beta-rhombohedral boron and boron carbide, the best-investigated icosahedral boron-rich solids, are reviewed. Because of its high density of gap states (~10
²¹
cm
^-3
) generated by intrinsic defects, p-type boron carbide behaves electronically extrinsic up to at least 2000 K, and therefore it exhibits excellent thermoelectric performance. This can even be considerably improved by suitable interstitial doping (Si, Al). As the possibility of n-doping of boron carbide can be largely excluded, other n-type counterparts are required for technical application. Some alkaline hexaborides (Takeda et al.) and rare-earth boron carbonitrides (Mori et al.) are shown to be promising candidates to close this gap