Possible mechanism for achieving glass-like thermal conductivities in crystals with off-center atoms

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  • 11 November 2003
Abstract
In the filled Ga/Ge clathrate, Eu and Sr are off-center in site 2 while Ba is on-center. All three filler atoms (Ba,Eu,Sr) have low temperature Einstein modes; however only for the Eu and Sr systems is there is a large dip in the thermal conductivity, attributed to the Einstein modes. No dip is observed for Ba. Here we argue that the off-center displacement plays two important additional roles - it enhances the coupling between the "rattler" motion and the lattice phonons, and the random occupation of different off-center sites produces a high density of symmetry-breaking defects which introduces another scattering mechanism at low T.

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