Effects of Sb Deviation from Its Stoichiometric Ratio on the Micro- and Electronic Structures and Thermoelectric Properties of CuSbS.

Thermoelectric material tetrahedrite CuSbS has attracted much attention because of its intrinsic low lattice thermal conductivity, excellent electrical transport property, and environment-friendly constituents. However, its thermoelectric figure merit, , is limited because of the low Seebeck coefficient () and power factor (PF). Hence, it is indispensable to enhance its and PF to increase its . Here, we show that when Sb deviation from its stoichiometric ratio in the CuSbS band structure is modulated, it gives rise to increased density of states and enhancement of the Seebeck coefficient. Moreover, carrier concentration is tuned by changing sulfur and copper vacancies through controlling the CuSbS phase with an atomic ratio of Sb, leading to increased electrical conductivity. In addition, as large as ∼60% reduction of lattice thermal conductivity is obtained by intensified phonon scattering using an impurity phase/element and vacancy-like defects induced by different Sb contents. As a result, a high = 0.86 is achieved at 723 K for the CuSbS sample with δ = 0.2, which is ∼50% larger than that of stoichiometric CuSbS studied here, indicating that of CuSbS can be improved through simple modulation of the Sb stoichiometric ratio.