Electrical/thermal transport and electronic structure of the binary cobalt pnictides Co Pn ₂ (Pn = As and Sb)

We demonstrate the electrical and thermal transport properties of polycrystalline CoPn₂ (Pn = As and Sb) between 300 and 900 K. CoAs₂ shows semiconducting electrical transport up to 900 K, while CoSb₂ exhibits degenerate conduction. Sign inversion of the Seebeck coefficient is observed at ∼310 and ∼400 K for CoAs₂ and CoSb₂, respectively. Thermal conductivity at 300 K is 11.7 Wm^-1K^-1 for CoAs₂ and 9.4 Wm^-1K^-1 for CoSb₂. The thermoelectric power factor of CoAs₂ is ∼10 μWcm^-1K^-2, although the dimensionless figure of merit is limited to ∼0.1 due to relatively high thermal conductivity. Using electronic structure calculations, the band gap value is calculated to be 0.55 eV for CoAs₂ and 0.26 eV for CoSb₂.