Effects of Ge Dopant on Thermoelectric Properties of Barium and Indium Double-Filled p-Type Skutterudites

Abstract

A series of Ge-doped and (Ba,In) double-filled p-type skutterudite materials with nominal composition Ba0.3In0.2FeCo3Sb12−xGex (x = 0 to 0.4, Δx = 0.1) have been prepared by melting, quenching, annealing, and spark plasma sintering methods. The effects of Ge dopant on the phase composition, microstructure, and thermoelectric properties of these materials were investigated in this work. A single-phase skutterudite material was obtained in the samples with 0 < x ≤ 0.2, and trace Fe3Ge2 was detected in the samples with x ≥ 0.3. The electrical conductivity increased and Seebeck coefficient decreased with increasing x in the range of 0 to 0.2, while the inverse behaviors of electrical conductivity and Seebeck coefficient were observed in the samples with x ≥ 0.3. The variations of electrical conductivity and Seebeck coefficient are attributed to the significant increase in the carrier concentration in the x range of 0 to 0.2 and the intensive impact of Fe3Ge2 when x ≥ 0.3. The lattice thermal conductivity of all the Ge-doped samples was considerably reduced as compared with the undoped Ba0.3In0.2FeCo3Sb12 sample, and the lowest value of lattice thermal conductivity of the Ba0.3In0.2FeCo3Sb11.8Ge0.2 sample reached 1.0 W m−1 K−1 at 700 K. The highest ZT value of 0.54 was obtained at 800 K for the Ba0.3In0.2FeCo3Sb11.7Ge0.3 sample, increased by 10% as compared with that of Ba0.3In0.2FeCo3Sb12.