Transport and thermoelectric properties of La_1-z Ce _z Fe_4-x Ni _x Sb₁₂ skutterudites

Abstract

La/Ce-double-filled skutterudites were prepared by encapsulated melting and hot pressing, and the double-filling effects on the transport and the thermoelectric properties were examined. The electrical conductivity decreased with increasing temperature, indicating that the La_1-z Ce _z Fe_4-x Ni _x Sb₁₂ skutterudites were degenerate semiconductors. All specimens showed positive Seebeck coefficients and Hall coefficients, confirming p-type conduction. The Seebeck coefficient increased with increasing temperature and Ni content, with the highest value being observed at temperatures ranging from 723 K to 823 K. The maximum power factor was obtained for La_0.25Ce_0.75Fe_3.75Ni_0.25Sb₁₂, with a peak value of 2.9 mWm ^-1K ^-2 at 723 K. The Seebeck coefficient decreased and the thermal conductivity increased due to bipolar conduction in the case of x = 0.25 for substitution of Ni at temperatures above 623 K and in the case of x = 0.5 for substitution of Ni at temperatures above 723 K. The lattice thermal conductivity decreased with increasing Ce content, regardless of Ni content. The electronic thermal conductivity decreased with increasing Ni content, resulting from the decrease in the carrier concentration. The dimensionless figure of merit (ZT) showed peak values at 723 K due to the decrease in the Seebeck coefficient (or the power factor) and the increase in the thermal conductivity at high temperatures. The maximum ZT of 0.76 was achieved at 723 K for La_0.25Ce_0.75Fe_3.75Ni_0.25Sb₁₂.