Local Structure of Cu in Cs8Na16Cu5Ge131 Type II Clathrate
Winnie K. Wong-Ng, Azzam Mansour, Matthew Beekman, George S. Nolas
We have used X-ray absorption spectroscopy (XAS) to investigate the local structure of Cu and Ge in the Cs8Na16Cu5Ge131 type II clathrate. We show that the local structure parameters, coordination number, and distances for Ge are consistent with those derived on the basis of XRD investigation of Cs8Na16Ge136. In addition, we confirm that Cu substitutes for Ge on the clathrate framework, but find that the Cu-Ge distance is smaller than the Ge-Ge distance by 0.13 Å, indicating a local distortion around the Cu atoms. The estimated degrees of disorder for Cu-Ge and Ge-Ge interactions indicate the Cu-Ge clathrate framework to be relatively stiff, while those for Na-Ge and Cs-Ge interactions corroborate previous observations of strong thermal disorder of the alkali guests in these materials.
Journal of Solid State Chemistry
local structure, Type II clathrate, Cs8Na16Cu5Ge131, thermoelectric, XAS