Fabrication and characterization of nanostructured thermoelectric Fe_xCo_1-xSb₃

Abstract

A novel synthesis route for the fabrication of p-type nanostructured skutterudite, FexCo1-xSb3 in large quantity is reported. This scalable synthesis route provides nano-engineered material with less impact on the environment compared to conventional synthesis procedures. Several Fe substituted compositions have been synthesized to confirm the feasibility of the process. The process consists of a nano-sized precursor fabrication of iron and cobalt oxalate, and antimony oxides by chemical co-precipitation. Further thermochemical processes result in the formation of iron substituted skutterudites. The nanopowders are compacted by Spark Plasma Sintering (SPS) technique in order to maintain nanostructure. Detailed physicochemical as well as thermoelectric transport properties are evaluated. Results reveal strongly reduced thermal conductivity values compared to conventionally prepared counterparts, due to nanostructuring. P-type characteristic was observed from the Seebeck measurements while electrical conductivity is high and shows metallic behavior. The highest TE figure of merit of 0.25 at 800 K has been achieved, which is strongly enhanced with respect to the mother compound CoSb 3 . This suggests the promise of the utilized method of fabrication and processing for TE applications with improved performance.

Collective Effect of Fe and Se To Improve the Thermoelectric Performance of Unfilled p-Type CoSb3 Skutterudites

“…Figure b shows a relative comparison of the reported ZT values for p-type CoSb 3 -based skutterudites, ,,− ,, which suggests that this value of ZT realized in the present study is far higher than those previously reported for p-type CoSb 3 unfilled skutterudites. ,,− ,, To govern the usefulness of the material, the average ZT has also been calculated and the comparison chart with previous reports is shown in Supporting Information (Section 4).…”

“…The highest reported ZT for pristine CoSb 3 synthesized through nanostructuring and hot pressed compaction is 0.17 at 610 K, 10,19 which is quite low due to its unoptimized carrier concentration; however, different approaches have been reported to enhance its ZT, which include doping, nanostructuring, and more recently employing a composite approach. 19−24 A ZT ∼ 0.2 at 700 K was reported in Fe doped p-type CoSb 3 prepared through encapsulated induction melting, 22 and the nanostructured Fe doped CoSb 3 synthesized by a chemical route resulted in a ZT ∼ 0.25 at 800 K. 20 Further, an enhanced ZT ∼ 0.53 at 823 K was reported by partial substitution of Fe on the Co-site in CoSb 3 , using a microwave assisted synthesis. 25 Moreover, the co-substitutions of Mn and Sn in CoSb 3 yielded a ZT ∼ 0.54 at 723 K, 26 which was the highest reported thus far in p-type doped-CoSb 3 unfilled skutterudites, although much higher values have been reported for their n-type counterparts.…”

“…Pristine binary skutterudite CoSb 3 behaves as a narrow band gap semiconductor, which generally exhibits bipolar conduction, − which can be favorably tuned to synthesize both n- and p-type TE materials by optimal doping. The highest reported ZT for pristine CoSb 3 synthesized through nanostructuring and hot pressed compaction is 0.17 at 610 K, , which is quite low due to its unoptimized carrier concentration; however, different approaches have been reported to enhance its ZT, which include doping, nanostructuring, and more recently employing a composite approach. − A ZT ∼ 0.2 at 700 K was reported in Fe doped p-type CoSb 3 prepared through encapsulated induction melting, and the nanostructured Fe doped CoSb 3 synthesized by a chemical route resulted in a ZT ∼ 0.25 at 800 K . Further, an enhanced ZT ∼ 0.53 at 823 K was reported by partial substitution of Fe on the Co-site in CoSb 3 , using a microwave assisted synthesis .…”

“…The experimental results suggest that the optimized partial substitutional doping of Fe at the Co-site and Se at the Sb-site in CoSb 3 results in a favorable tuning of the electrical and thermal transport properties leading to an enhanced ZT, which is nearly 4 times that reported earlier for its pristine counterpart. 19 On the basis of the reported studies, as the maximum ZT in doped CoSb 3 has been achieved for Fe doping concentration 20−30%, 20,22,27 accordingly we have fixed the Fe doping concentration at the Co-site at ∼25% and then the TE properties have been studied for different compositions by varying the Se doping concentration. In CoSb 3 , while the Fe substitution on the Co-site results in a ptype conduction, the Se doping on the Sb-site leads to favorable tuning of the carrier concentration, resulting in enhanced electrical transport properties.…”

Thermoelectric Properties of Sulfur-Filled and Iron-Substituted Co4Sb12

“…The motivation for choosing an acceptor-type Fe dopant is to synthesize a p-type Co 4 Sb 12 because substituting a n-type dopant at the Co/Sb site makes the material n-type. Among p-type dopants in Co 4 Sb 12 , Fe (4s 2 3d 6 ) is a promising candidate, having one less electron than Co (4s 2 3d 7 ). − However, as both filler and dopant are p-type, it will create a charge imbalance in the system. Therefore, a minimal amount of filler can be added to the voids in combination with p-type dopants.…”