Thermal conductivity of YbB44Si2

The low temperature thermal conductivity of YbB44Si2 is investigated. The rare earth boron icosahedra compounds are of interest as potential high temperature thermoelectric materials. The thermal conductivity of YbB44Si2 is relatively large below room temperature, showing crystalline behavior and having a peak exceeding 10 W/m/K at ∼35 K. This departs markedly from the low amorphouslike behavior observed in another rare-earth-containing boron cluster compound: RB66 (R=rare earth). From a comparison and consideration of the various models, we conclude that disorder is the important factor in the generally observed low thermal conductivities of these compounds, with RB66 being exceptionally disordered as compared to YbB44Si2.