Effect of La filling on thermoelectric properties of LaxCo3.6Ni0.4Sb12-filled skutterudite prepared by MA–HP method

Starting from elemental powder mixtures, single-phase LaxCo3.6Ni0.4Sb12(image, 0.1, 0.4, 0.6)-filled skutterudites were synthesized via the route of mechanical alloying–hot pressing (MA–HP) in this paper. With increasing of La fraction, the lattice spacing of filled skutterudite phase increases and its variation follows the Vegardʹs law. The magnitude of the Seebeck coefficient and electrical resistivity show slight increases with increasing of La filling fraction; thermal conductivity of the filled skutterudite decreases and the resultant figure of merit increases with increase of La filling fraction. The as-HPed filled skutterudite has a composite nanocrystalline microstructure, which includes some coral-like clusters with relatively large spoke-like grains about 300 nm in length and a superfine equiaxial nanocrystalline matrix with an average grain size of about 50 nm. The coral-like cluster corresponds to the prime filled skutterudite formed directly by MA, while the filled skutterudite formed during hot pressing, which has the same nucleation condition and experiences less grain growth, develops equiaxially into the superfine nanocrystalline matrix.