Effect of In Impurity on Thermoelectric Properties of Ba and In Double-Filled n-Type Skutterudite Materials

A series of (Ba,In) double-filled -type skutterudite materials with nominal composition Ba0.4In Co4Sb12 ( = 0 to 0.4, Delta = 0.1) has been prepared by melt quenching, annealing, and spark plasma sintering (SPS). The presence of In impurity and its effect on the thermoelectric properties of the filled skutterudite materials have been precisely investigated in this work. All samples consisted of skutterudite phase, while traces of In-containing impurity were detected in samples with >= 0.3. The electrical conductivity and thermal conductivity decreased, and the absolute value of the Seebeck coefficient increased with increasing in the range 0 to 0.2; however, the inverse behavior of the electrical conductivity, thermal conductivity, and Seebeck coefficient was observed in the samples with >= 0.3. The thermoelectric properties of Ba0.4In Co4Sb12 in the range of 0 to 0.2 were changed because of carrier concentration degradation and strong lattice scattering induced by the In filler, while they were intensively affected by the In-containing impurity for >= 0.3. Compared with the Ba single-filled skutterudite material, the power factors of all (Ba,In) double-filled skutterudite materials significantly increased and the lattice thermal conductivity dramatically decreased. As a result, two large values for the samples with = 0.2 and 0.4 reached 1.19 and 1.25 at 800 K, which is an enhancement of 52% and 60%, respectively.