Preparations And Thermoelectric Properties Of Iodine-filled Cosb₃-based Skutterudite

As for a thermoelectric material, CoSb3-based antimonide skutterudites haveexcellent electrical properties, but poor thermal properties. Researchers found that thereare two voids two big lattice voids in skutterudite unit cell that can be filled by filler atomswith an ionic radius lower than the cage radius acting as “rattlers” to enhance phononscattering without disturbing the electrical transport. Moreover, partial substitution on Coor Sb-site has the advantage to adjust the carrier transport properties that optimizeelectrical performance and introduce lattice distortions that suppress lattice thermalconductivity.Dr. Fukuoka successfully synthesized I-filled I0.9Rh4Sb12using high pressuresynthesis (HPS) technique. Iodine filling into the lattice voids reveals anionic state I-andthe I-filled p-type I0.9Rh4Sb12is the only anion-filled skutterudite in the releasedpublications. The filling fraction as high as0.9evaluated. Such a high fraction isbeneficial for suppressed thermal conductivity. It is therefore motivating to exploreI-filled IyCo4Sb12using high pressure synthesis (HPS) technique. The p-type I0.79Co4Sb12were successfully synthesized by a three-step synthetic method using high pressuresynthesis technique and the thermal conductivity as low as0.7W/mK achieved was thelowest in skutterudites to date. However, the semiconductor behaviour leaves highelectrical resistivity and thereby pulls down the ZT.We use two ways to improve thermoelectric performace of I-filled skutterudites byoptimizing preparations and by Fe substisuting on Co to improve the thermoelectric properties.The former includes two aspects. One is to explore the suitable sintering pressure. Theresults show that the best sintering pressure and temperature are3Gpa and573K,respectively. A ZT value of0.26was achieved. In comparison to the sintering pressure1GPa and sintering temperature573K, the ZT was improved by44％. The other is Agnano-powders into skutterudite matri. An enhanced ZT value of0.32was achieved. Incomparison to the parent the ZT,23％improvement was achieved. The samples regardingFe substituting on Co show improved electrical properties and at the mean time maintaining low thermal conductivity. Therefore ZT is two-fold comparing withno-replacement and unfilled samples. The results suggests that iodine as filler applicableto other single-and multiple-filled skutterudites to further suppressing thermalconductivity.