2, Department of Energy, Ames, Iowa, United States
3, Sandia National Laboratories, Livermore, California, United States
4, Laboratoire CRISMAT, Caen, , France
Thermoelectric materials which can directly convert waste heat into electrical power and vice versa, have potential to improve our society energy efficiency. Clathrate compounds are good thermoelectric materials due to their unique structural motif with three-dimensional host frameworks encapsulating guest atoms in large oversized cages. The “rattling” behavior of guest atoms in the cages results in the low thermal conductivity of clathrate compounds. An enclathration of small trivalent rare-earth cations was predicted to enhance the power factor of clathrate and overall thermoelectric performance. Ba8Cu16P30 clathrate, which exhibits the smallest size of the pentagonal dodecahedral cages among all clathrates, was chosen to be a clathrate host for the La and Ce rare-earth guests. The unambiguous proofs of incorporation of rare earth elements into cages were proved by a combination of synchrotron powder diffraction, time-of-flight neutron powder diffraction, scanning-transmission electron microscopy, and electron energy-loss spectroscopy. Our quantum-mechanical calculations and experimental characterizations show that the incorporation of the rare-earth cations significantly enhances the hole mobility and concentration which results in the drastic increase in the thermoelectric performance.