Thermoelectric Properties of Sulfur-Filled and Iron-Substituted Co₄Sb₁₂

Abstract

Filling the voids of a skutterudite material using suitable electropositive elements majorly affects the power factor by altering the carrier concentration. The mass difference of the filler with constituent elements leads to a lower lattice thermal conductivity and consequently increases the figure of merit. The combination of doping and filling can further improve thermoelectric properties. Usually, the type of bonding between the fillers and host atoms is decided by the difference in their electronegativity values. Electropositive elements have been successfully used as n-type fillers in Co 4 Sb 12 . The doping of electron donors at the Co or Sb site helps to incorporate electronegative elements into the voids by the charge compensation between a n-type dopant and a p-type filler. In this study, a p-type dopant Fe has been substituted in the Co site of S 0.15 Co 4 Sb 12 . A series of S 0.15 Fe x Co 4−x Sb 12 (x = 0.05−0.9) samples were prepared by a solid-state reaction. CoSbS, Sb secondary phases were noticed in the samples with x = 0.05 and 0.1 and FeS, Sb secondary phases were observed in the samples with x ≥ 0.2. The filling content of S into the void was ∼0.04 for S 0.15 Co 4 Sb 12 , which decreased with the increasing Fe content. The Seebeck coefficient was positive, indicating that holes are the majority of charge carriers. An increase in carrier concentration was observed with the increase in the Fe content, which reduced the Seebeck coefficient and electrical resistivity. The thermal conductivity was reduced for the samples with x = 0.1 and 0.9 compared to the sample S 0.15 Co 4 Sb 12 due to Fe doping in the Co site and S filling in the void site. The highest zT of ∼0.30 at 773 K was obtained for S 0.15 Fe 0.9 Co 3.1 Sb 12 .

Enhancement in Thermoelectric Performance in Ti-doped Yb0.4Co4Sb12 Skutterudites via Carrier Optimization and Phonon Anharmonicity

“…In addition, the substitution of Fe at the Co site affected the vibrational spectrum of the Sb 4 ring which led to the low thermal conductivity value of 1.75 W/(m·K) . Further, a material for thermoelectric use is expected to feature both n- and p-type conduction. − Recently, a fast and very efficient method of fabrication was introduced by Li et al, in an n-type Yb-containing CoSb 3 system, where the rapid crystallization was seen to be beneficial to provide the single phase of CoSb 3 , without a CoSb 2 phase, with nano/microsized and radial-like grains, assisting two peritectic reactions via Yb filling . As a result, the deformation potential ( E def ) is also reduced, which provides an increase in the effective mass.…”