CERIUM FILLING AND DOPING OF COBALT TRIANTIMONIDE

We have fabricated and studied the structural, magnetic, and transport properties of filled skutterudites of the form CeyFe4-xCoxSb12 with 0 < y < 1 and x=3.25 and 4. For samples containing 100% Co, Ce can be i nserted into approximately 10% of the voids in the skutterudite struct ure. It is shown that the rare earth is trivalent and dopes the host C oSb3 n-type. With substitution of Fe for Co the void occupancy by Ce i ncreases. The thermal conductivity is strongly depressed even at small (5%) rare-earth filling fractions, and is further degraded by substit ution of Fe for Co. Although the electron mobility in n-type samples i s 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.