Enhancement of the thermoelectric properties of MnSb₂Se₄ through Cu resonant doping

MnSb₂Se₄ is a narrow band semiconductor having large Seebeck coefficients and intrinsically low thermal conductivities, but modest thermoelectric zT values due to having low carrier concentrations and high electrical resistivity. Here, we report that Cu substituted Mn_1-xCu_xSb₂Se₄ (0 ≤ x ≤ 0.35) materials display resonant doping behavior, leading to significantly enhanced power factors (PFs) and overall thermoelectric zT values in the measured temperature range. For the optimized composition Mn_0.75Cu_0.25Sb₂Se₄, the PF reaches 0.26 mW m^-1 K^-2 at 773 K, coupled with low thermal conductivities of 0.61 W K^-1 m^-1 to 0.32 W K^-1 m^-1 over the measured temperature range. A peak zT of 0.64 at 773 K is achieved, which is a 100% increase in comparison to undoped MnSb₂Se₄. Such a high zT has rarely been seen in thermoelectric materials with a low symmetry of crystallization, implying that Cu-doped MnSb₂Se₄ could be considered as a new platform in thermoelectric research for intermediate temperature power generation.