Colossal Seebeck coefficient in strongly correlated semiconductor FeSb₂

For more than a decade strongly correlated semiconductors and Kondo insulators have been considered as potential thermoelectric materials. Such materials have large d- or f-character of the electronic band structure close to the Fermi level that theoretically leads to Seebeck coefficients (S) with large magnitudes. In this work it is shown for the first time that the strongly correlated semiconductor FeSb₂ exhibits a colossal Seebeck coefficient of ∼−45000 μVK⁻¹ at 10 K. The thermoelectric power factor PF=S²·ρ⁻¹, where ρ is the electrical resistivity, reaches a record high value of ∼2300 μWK⁻² cm⁻¹ at 12 K and is 65 times larger than that of the state-of-the-art Bi₂Te₃-based thermoelectric materials. However, due to a large lattice thermal conductivity the dimensionless thermoelectric figure of merit is only 0.005 at 12 K. Nonetheless, the potential of FeSb₂ as a future solid-state thermoelectric cooling device at cryogenic temperatures is underlined.