Preparation of La-filled skutterudites by mechanical alloying and hot pressing and their thermal conductivities

La-filled and Fe-substituted skutterudites LaxFeCo3Sb12 (x = 0.2, 0.4, 0.6, 0.9) were prepared by mechanical alloying (MA) and hot pressing (HP) in this paper. X-ray diffraction and field-emission-gun scanning electron microscopy were performed to characterize the phase transformation during the MA-HP process. Skutterudite phase appeared after milling for 10 h, and (Co, Fe)Sb2 phase was synthesized with further prolonging the milling time. Although single-phase filled skutterudite could not be directly obtained even milled over 40 h, it was successfully produced by hot pressing the powders milled for 10 h at 650 °C for 2 h under a pressure of 50 MPa. A great reduction of the thermal conductivity of the hot-pressed samples was obtained, and the thermal conductivity decreased with increasing of La-filling fraction.