Probing Phonon Scattering Sites in the Thermoelectric Clathrate Eu8Ga16Ge30

The low thermal conductivity of the Thermoelectric Clathrates Eu₈Ga₁₆Ge₃₀ and Sr₈Ga₁₆Ge₃₀ has been attributed to rattling atoms (Eu or Sr) in the Eu2/Sr2 sites. The low Einstein temperature obtained using XAFS for the nearest neighbor Eu-Ga/Ge bonds at the Eu2 sites is consistent with the model. However, the comparable Einstein temperature for the Eu1 site indicates that Eu1 is also a rattler. The fit also confirms that the Eu2 is displaced along either the y or z axis ～ 0.45Å in agreement with neutron diffraction.