Session A26 - Focus Session: Thermoelectric Materials and Novel Thermoelectric Phenomena I.
FOCUS session, Monday morning, March 18
206, Indiana Convention Center
We have studied the electronic and vibrational properties of some Sn-based Type II clathrate materials using LDA electronic structure methods. These framework materials have open cages which can contain guest impurities and such guests can produce local (``rattling'') vibrational modes. These modes may scatter the extended, heat carrying acoustic modes of the framework, potentially reducing the thermal conductivity. Results are presented for the electronic bandstructures and for the vibrational spectra of the Type II clathrate framework Sn_136 and of the compounds Cs_24Sn_136 and Na_16Cs_8Sn_136. We have also theoretically identified the infrared- and Raman-active modes in these materials and have computed their Raman spectra. We focus on the vibrational frequencies of the guests and thus identify the low frequency, guest-related ``rattling'' vibrational modes in these materials.