Improvement of Thermoelectric Performance and P-N Control for Metal-Doped β-Rhombohedral Boron

The effects of Cu-doping into beta -rhombohedral boron on the thermoelectric properties have been investigated. The electrical conductivity increases with increasing Cu concentration up to 5 at%, while a positive Seebeck coefficient monotonically decreases because of an increase in the carrier concentration. Consequently, the power factor enhances by four times from 22 mu W m-1 K-2 to 90 mu W m-1 K-2 at 973 K. In addition, Cu-doping contributes to lower the thermal conductivity from 4.3 W m-1 K-1 to 2.3 W m-1 K-1 at 973 K due to an increase in phonon scattering events. The dimensionless figure of merit, ZT, enhances from 0.006 to 0.038 at 973 K for Cu4B105 as p-type. The observed ZT is higher than that of conventional thermoelectric boride B4C.