High-temperature thermal conductivity of thermoelectric clathrates

We have carried out an evaluation of the lattice thermal conductivity for 19 different type-I intermetallic clathrate compositions at temperatures near or above their respective Debye temperatures. Although the low temperature data (T < 300 K) show that the thermal transport can vary from glasslike to crystalline depending on the composition, the high temperature lattice thermal conductivity values (T > 300 K) appear to be relatively well described by a simple model that assumes only anharmonic three-phonon scattering processes. The analysis suggests the large number of atoms in the unit cell accompanied by a significant degree of anharmonicity and relatively low Debye temperatures produce low lattice thermal conductivities in these materials above 300 K, regardless of composition or the nature and influence of guest rattling behavior on thermal transport below room temperature. The dominant mechanism underlying the universally low lattice thermal conductivity of type-I intermetallic clathrates (ranging from similar to 0.6 to similar to 2 W/m K) in the temperature regime of importance for thermoelectric power generation is therefore clarified. Published by AIP Publishing.