We have fabricated and studied the structural, magnetic, and transport properties of filled skutterudites of the form ${\mathrm{Ce}}_y{\mathrm{Fe}}_{4-x}{\mathrm{Co}}_x{\mathrm{Sb}}_{12}$ with 0< $y$<1 and $x$=3.25 and 4. For samples containing 100% Co, Ce can be inserted into approximately 10% of the voids in the skutterudite structure. It is shown that the rare earth is trivalent and dopes the host Co${\mathrm{Sb}}_3$ $n$-type. With substitution of Fe for Co the void occupancy by Ce increases. The thermal conductivity is strongly depressed even at small (5%) rare-earth filling fractions, and is further degraded by substitution of Fe for Co. Although the electron mobility in $n$-type samples is smaller than the hole mobility in $p$-type samples, due to their large electron masses the Seebeck coefficient in $n$-type material maintains large values at high electron concentrations.

• Received 20 May 1997

DOI:https://doi.org/10.1103/PhysRevB.56.7376