The doubly filled skutterudite (La,Sm) (Fe Ni1-)4Sb12 (y = 0.19–0.70, x = 0.52–0.85): Structural and thermoelectric features

A comprehensive investigation of the double-filled skutterudite system (La,Sm)y(FexNi1-x)4Sb12 (y = 0.19–0.70, x = 0.52–0.85) has been carried out with the aim of exploring the influence of multi-filling with rare-earth elements on the structural and thermoelectric properties of the material. The introduction of La alongside Sm leads to a progressive increase in the filling degree as the Fe content increases, associated with structural modifications without evident slope changes in the cell parameter. The p/n crossover is identified at x ∼ 0.67 and y ∼ 0.45, and it is bound to changes in several physical parameters. Thermoelectric measurements reveal notably low thermal conductivity values in heavily filled compositions, attributed to enhanced phonon scattering due to the mass contrast and rattling effects of the two different fillers. As a result, the sample with x = 0.79 and y = 0.65 achieves a remarkable ZT value of approximately 1 at 650 K. These outcomes confirm that double-filling with La and Sm represents an effective strategy to reduce lattice thermal conductivity and improve the thermoelectric performance in Fe/Ni-based skutterudites.