First-principles Review of Thermoelectric Properties of CuFeS2 and the Effect of Nanostructuring

Composed of inexpensive and naturally abundant elements, the chalcopyrite mineral CuFeS2 has received attention as a potentially useful thermoelectric. We show that first-principles density-functional theory calculations of thermoelectric properties of n-doped CuFeS2 can successfully reproduce experimental measurements, including the Seebeck coefficient. High values of the Seebeck coefficient are attributed to the strong energy-dependence of group velocities in multiple heavy-effective-mass electronic pockets near the conduction band edge. However, flat band dispersion also leads to low mobility, which forces one to rely on high carrier concentration to achieve high conductivity. This decreases the optimal Seebeck coefficient and limits the achievable power factor. Our calculations predict that ideally doped and nanostructured (to grain size of 20 nm) CuFeS2 can increase zT approximately 5-fold relative to the bulk due to significant reductions in the lattice thermal conductivity, attaining zT = 0.25-0.8 at T=300-700 K.