Effects of Sb Deviation from Its Stoichiometric Ratio on the Micro-and Electronic Structures and Thermoelectric Properties of Cu12Sb4S13

Thermoelectric material tetrahedrite Cu12Sb4S13 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, ZT, is limited because of the low Seebeck coefficient (S) and power factor (PF). Hence, it is indispensable to enhance its S and PF to increase its ZT. Here, we show that when Sb deviation from its stoichiometric ratio in the Cu12Sb4S13 band structure is modulated, it gives rise to increased density of states and enhancement of the Seebeck coefficient. Moreover, carrier 300 490 500 600 700 T (K) concentration is tuned by changing sulfur and copper vacancies through controlling the Cu3Sb4S4 phase with an atomic ratio of Sb, leading to increased electrical conductivity. In addition, as large as similar to 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 ZT = 0.86 is achieved at 723 K for the Cu12Sb4+delta S13 sample with (delta = 0.2, which is similar to 50% larger than that of stoichiometric Cu12Sb4S13 studied here, indicating that ZT of Cu12Sb4S13 can be improved through simple modulation of the Sb stoichiometric ratio.