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 Ni0.07Co0.93Sb3. 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 Ni0.07Co0.93Sb2.94Te0.06. 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.