2003/11/30 by F. Bridges, L Downward, L. Downward · 2 citations
Materials Science · Physics and Astronomy · #Advanced Thermoelectric Materials and Devices #Material Dynamics and Properties #Thermal properties of materials #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevb.70.140201
published as Phys. Rev. B 70, 140201 (2004) · 4 pages, 1 figure (2 parts) -- v2: intro broadened; strengthened arguments regarding need for additional phonon scattering mechanism
arxiv created 2004/06/30 · openalex publication_date 2004/10/05 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
In the filled Ga∕Ge clathrate, Eu and Sr are off center in site 2 but Ba is on center. All three filler atoms (Ba,Eu,Sr) have low-temperature Einstein modes; yet only for the Eu and Sr systems is there a large dip in the thermal conductivity, attributed to the Einstein modes. No dip is observed for Ba. 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 Eu and Sr systems, and turns on/off another scattering mechanism (for 1\phantom\rule0.3em0exK<T<20\phantom\rule0.3em0exK) 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.