Enhancing the thermoelectric power factor of metal/tetrahedrite nanocomposites via phase boundary engineering

Abstract

Tetrahedrite is an important thermoelectric material due to its low lattice thermal conductivity (κ_l) and relatively high figure-of-merit (zT_max). Further enhancement of zT parameter is expected through the enhancement of the power factor (PF) by decoupling the interdependence between electrical conductivity (σ) and Seebeck coefficient (S). In order to do that, in this work, we propose to act on the phase boundaries of the tetrahedrite (Cu₁₂Sb₄S₁₃) composites with metal (Ag, Ni) nanoinclusions. These composites, with nominal metal compositions of x = (0.0, 0.5, 1.0, 2.0, 4.0) wt. %, were synthesized by a solution-based bottom–up approach. The structure and microstructure of the Cu₁₂Sb₄S₁₃–[Ag, Ni] composites were characterized using X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray analysis. The charge carrier transport and its scattering mechanisms were investigated by examining the σ–T and S–T dependencies, followed by calculations of the maximum power factor (PF_max), average power factor (PF_avg), electronic thermal conductivity (κ_e), weighted mobility (μ_w), potential energy barrier (E_b), and electronic quality factor (B_E). In Ag-based composites, the PF_avg improved in respect to the tetrahedrite matrix by ∼20 % in the temperature range of 298–413 K at x_Ag = 0.5 and 1.0 wt % due to the charge carrier filtering through Schottky barriers at the Ag/Cu₁₂Sb₄S₁₃ interfaces. In Ni-based composites, the PF_avg increased by ∼15 % in the same temperature range for x_Ni = 0.5 wt % as a result of the charge carrier accumulation (modulation doping) facilitated by Ohmic barriers at the Ni/Cu₁₂Sb₄S₁₃ interfaces.