Significant enhancement of electrical conductivity by incorporating carbon fiber into CoSb3 thermoelectric skutterudite fabricated by spark plasma sintering method

Abstract

The effects of carbon fiber additions on the electrical, thermoelectric, and magnetotransport performance in p-type CoSb3-based skutterudite are reported. A three-fold enhancement in electrical conductivity and a large increase in magnetoresistance are found. Two different explanations for the increased electrical conductivity are considered; either that carbon atoms form cause defects that makes the CoSb3 more conductive, or that the increase in conductivity is due to electrical percolation of the carbon fibers in the composite. X-ray diffraction data show that the lattice parameter of the CoSb3 is not affected by the presence of the carbon fiber, however adding carbon causes precipitation of 20 wt. % elemental Sb. DFT calculations show that the enthalpy of formation of a solid-solution of carbon (both interstitial and as a substitution for Sb) is favorable. These results support an explanation based on an improved electrical conductivity of a dilute solid solution of C in CoSb3. The average thermoelectric parameters of the composite material, including heat conductivity, average composite Seebeck coefficient, Hall effect, carrier mobility and carrier concentration were influenced by the carbon addition. Unfortunately, the effects largely cancel each other so that the overall zT of the composite was not improved. Finally, large room temperature magnetoresistance (up to 90% at 13T) is observed, which increases with content of carbon fiber.

Insights into the Classification of Nanoinclusions of Composites for Thermoelectric Applications

“…Carbon is commercially available, lightweight, inexpensive, and has excellent semiconductive properties to add as a nanoinclusion to improve thermoelectricity. Carbon allotropes such as fullerene, ,− carbon black, ,, carbon fiber, graphite, carbon nanotubes, ,− and graphene ,,,, are used as nanoinclusions to improve thermoelectric performance. Generally, carbon-based nanoinclusions are added to tailor both the electrical and the thermal properties due to the high concentration of charge carriers associated with them .…”

“…73 The thermoelectric performance and mechanical stability of Cu 3 SbS 4 were strongly enhanced by adding carbon black nanoinclusions, as shown in Figure 7d−i. 73 Hossain et al 89 added carbon fiber to the CoSb 3 matrix and observed a substantial increase in the electrical and thermal conductivity due to carbon atom doping. It is also reported that adding graphite nanoinclusions to the bismuth telluride increases σ, decreases κ, and improves the S simultaneously.…”