Compound Defects and Thermoelectric Properties of Self-Charge Compensated Skutterudites SeyCo4Sb12-xSex.

In the past two decades, many studies have focused on the effects of electropositive guest fillers on the electrical and thermal transport properties in CoSb3-based skutterudites. Recently, some electronegative elements such as S, Se, Cl, and Br have been filled into the voids in CoSb3 with a small amount of n-type dopant Te on the Sb sites. In this report, self-charge compensated skutterudites SeyCo4Sb12-xSex (0 < x + y < 0.9) with Se occupying two different atomic sites have been fabricated by a traditional melting-annealing process combined with a spark plasma sintering method. Phase purity was determined by X-ray diffraction, and the microstructures were examined by scanning electron microscopy. The temperature dependencies of the electrical and thermal transport properties were characterized. Se could enter both the void and Sb sites in CoSb3 with a solubility limit around 0.6. The Se content has little effect on bandgap. Similar to Ga dual-site occupied GayCo4Sb12-xGax (y = 2x), a typical semiconducting electrical property with a low carrier concentration as well as a large Seebeck coefficient is observed. A correlation between the large Seebeck coefficient and the carrier scattering mechanism has been proposed. In addition, a largely reduced room temperature lattice thermal conductivity is obtained with a minimum value of 2.1 Wm-1 K-1 for Se0.2Co4Sb11.6Se0.4. The effects of Se on lattice thermal conductivity and filler resonant frequency are discussed.