Synthesis of electronegative S-filled and Sn–Te double substituted skutterudite compounds by HPHT and its thermoelectric properties

Electronegative S-filled skutterudite compounds have attracted considerable attention due to scattering of low-frequency phonons (35–50 cm − 1 ), but there are few reports on S-filled double-substituted skutterudite. In this work, a series of S-filled Te-Sn double-substituted skutterudite compounds were synthesized using high pressure and high temperature (HPHT) method. The phase composition, microstructure, and thermoelectric properties of S x Co 4 Sb 1 1 Te 0 . 7 Sn 0 . 3 ( x = 0 , 0.05, 0.10, 0.20) samples were systematically determined. The results show that the introduction of S increases the substitution limit of Te in the Sb site. Under the combined effect of the sample synthesis pressure and S filling, the nucleation density of the sample grains increases and the grain size decreases. At the same time, there are numerous special microstructures in the samples synthesized in a high-pressure environment. Thermoelectric performance studies show that a small amount of S filling optimizes the Seebeck coefficient of the sample and increases the power factor (PF). With an increase of the amount of S introduced, the thermal conductivity of the samples decreases significantly. Therefore, the maximum zT value of an S 0 . 0 5 Co 4 Sb 1 1 Te 0 . 7 Sn 0 . 3 sample synthesized at 2.5 GPa pressure is 0.17 at room temperature. The maximum zT value of the sample is 1.26 at 773 K.