Abstract
In the filled clathrate, and are off center in site 2 but is on center. All three filler atoms have low-temperature Einstein modes; yet only for the and systems is there a large dip in the thermal conductivity, attributed to the Einstein modes. No dip is observed for . Here we argue that it is the off-center displacement that is crucial for understanding this unexplained difference in behavior. It enhances the coupling between the “rattler” motion and the lattice phonons for the and systems, and turns on/off another scattering mechanism (for ) produced by the presence/absence of off-center sites. The random occupation of different off-center sites produces a high density of symmetry-breaking defects which scatter phonons. It may also be important for improving our understanding of other glassy systems.
- Received 23 October 2003
DOI:https://doi.org/10.1103/PhysRevB.70.140201
©2004 American Physical Society