Multitemperature synchrotron powder diffraction and thermoelectric properties of the skutterudite La0.1Co4Sb12

Abstract

Compounds with the skutterudite structure have potential use in thermoelectric power generation and the role of the filler atoms in filled skutterudites is still an open question regarding their effects on thermal conductivity. Partially filled skutterudite La0.1Co4Sb12 has been investigated by synchrotron powder x-ray diffraction between 90 and 700 K, as well as heat capacity, electrical and thermal transport property measurements, and Hall effect measurements. Anomalously large atomic displacement parameters (ADPs) are found for the La filler atoms, indicating that the La atoms are weakly bound in the structure. Analysis of the multitemperature ADPs of La using the Einstein model and the ADPs of the framework atoms using the Debye model gives an Einstein temperature of 79 K and a Debye temperature of 268 K. The heat capacity estimated from the Debye and Einstein temperatures is in good agreement with the measured experimental data. The ADP analysis also indicates that the La atoms are slightly displaced (0.06 Å) from the cage center possible due to covalent bonding with the host structure. Compared with unfilled CoSb3, the low energy La vibration modes significantly increase the heat capacity of La0.1Co4Sb12 at lower temperature despite the low La occupancy (refined occupancy of 4.9%). The small content of filling atoms results in a large reduction in the thermal conductivity.