Improvement in Thermoelectric Performance of Cu-Doped β-Rhombohedral Boron

Abstract

The effects of Cu doping on the thermoelectric properties of β-rhombohedral boron have been systematically investigated using nominal compositions of Cu_xB₁₀₅ (x = 0–5). The electrical conductivity increases with increasing x up to 5 at.%, whereas the positive Seebeck coefficient decreases because of an increase in the carrier concentration. Consequently, the power factor is enhanced by a factor of four from 22 μW m⁻¹ K⁻² (x = 0) to 90 μW m⁻¹ K⁻² (x = 4) at 973 K. In addition, Cu doping of the interstitial D and E sites contributes a ~50% reduction in the thermal conductivity from 4.3 W m⁻¹ K⁻¹ (x = 0) to 2.1 W m⁻¹ K⁻¹ (x = 5) at 973 K because of increased numbers of phonon scattering events. The dimensionless figure of merit ZT is also enhanced by a factor of six from 0.006 (x = 0) to 0.038 (x = 4) at 973 K in the p-type material. The ZT value obtained is higher than that of the conventional thermoelectric boride B₄C.