High figure of merit in Ce-filled skutterudites

New thermoelectric materials with superior transport properties at high temperatures have been discovered. These materials are part of the large family of skutterudites, a class of compounds which have shown a good potential for thermoelectric applications. The composition of these novel materials, called filled skutterudites, is derived from the skutterudite crystal structure and can be represented by the formula LnT/sub 4/Pn/sub 12/ (Ln=rare earth, Th; T=Fe, Rn, Os, Co, Rh, Ir; Pn=P, As, Sb). In these compounds, the empty octants of the skutterudite structure which are formed in the TPn/sub 3/ (/spl sim/T/sub 4/Pn/sub 12/) framework are filled with a rare earth element. Some of these compositions, based on CeFe/sub 4/Sb/sub 12/, have been prepared by a combination of melting and powder metallurgy techniques and have shown exceptional thermoelectric properties in the 350-700/spl deg/C temperature range. At room temperature, CeFe/sub 4/Sb/sub 12/ behaves as a p-type semimetal, but with a low thermal conductivity and surprisingly large Seebeck coefficient. These results are consistent with some recent band structure calculations on these compounds. Replacing Fe with Co in CeFe/sub 4/Sb/sub 12/ and increasing the Co:Fe atomic ratio resulted in an increase in the Seebeck coefficient values. The possibility of obtaining n-type conductivity filled skutterudites for Co:Fe values higher than 1:3 is currently being investigated. Measurements on bulk samples with a CeFe/sub 3.5/Co/sub 0.5/Sb/sub 12/ atomic composition and p-type conductivity resulted in dimensionless figure of merit ZT values of 1.4 at 600/spl deg/C.