Synergistic Optimization of Electronic and Thermal Transport Properties for Achieving High ZT in Ni and Te Co-substituted CoSb₃

The current work aims to explore the enhancement in thermoelectric performance of CoSb₃-based materials via doping with less expensive rare-earth-free dopants. For this purpose, Te was chosen as a dopant on the Sb site in pre-optimized parent alloy Ni_0.07Co_0.93Sb₃. The facile and fast synthesis route of arc melting and spark plasma sintering was utilized to prepare uniform and dense samples. The structural and transport properties were experimentally measured over a range of temperatures. As a result of suitable optimization of thermal and electronic transport properties, a state-of-the-art ZT value of ∼0.9 at 870 K was achieved for the composition Ni_0.07Co_0.93Sb_2.94Te_0.06. This acquired value of peak ZT is ∼50% enhanced from the parent compound, which is majorly attributed to the augmented power factor. In order to analyze this huge increment, first-principles-based density functional theory calculations were performed. Ni doping in CoSb₃ is found to result in an n-type doped semimetal. The co-doping with Te at the Sb site was effective in opening a gap resulting in a heavily doped n-type semiconductor with a higher power factor than the Ni-doped one. Further, the theoretically calculated electronic transport properties were found in agreement with those observed experimentally for the synthesized samples.