Enhancement of the Thermoelectric Properties and Transition of Conduction Mechanism from Nearest Neighbor to Variable Range Hopping of Ni-Doped CoSb3

The temperature-dependent electrical resistivity of the Ni-doped CoSb 3 system (Ni= 0, 1, 3, and 5 at.%) was carried out to identify the conduction mechanism at the different temperatures. The samples were prepared by solid-state reaction and characterized by x-ray diffraction (XRD) and Raman spectroscopy. The XRD pattern confirms the CoSb 3 phase for the pristine sample while the NiSb 2 compound is identified as an impurity phase for Ni content > 3 at.%. Five out of eight Raman active modes are evident in the pristine sample indicating the formation of the Skutterudite phase. Ni in CoSb 3 acts as an electron donor and hence decreases the resistivity approximately seven times at low temperature. The temperature-dependent Seebeck coefficient exhibits an increase in magnitude with doping concentration and a negative value is observed for all the samples indicating the formation of n -type skutterudite. The results of the thermoelectric properties are promising due to the significant increase in power factor (282 µW/mK 2 ) for the doped sample. The temperature-dependent electrical resistivity analysis reveals that in the high-temperature regime (285–400 K), there is a dominance of thermally activated band conduction while in the lower temperature region (< 280 K), the hopping conduction is dominant. The detailed analysis of the temperature variation of resistivity shows that in the temperature range from (190–280 K), nearest-neighbor hopping (NNH) dominates, whereas, in the lower temperature region, Mott's variable range hopping (VRH) is the dominant conduction mechanism. T dev , at which VRH occurs is 180 K for pristine CoSb 3 and is found to decrease with Ni doping concentration and is attributed to the increase in the density of states at the Fermi level. Graphical Abstract