Copper containing germanium clathrates

Calculated transport properties based on density functional theory calculations for Ba₈Cu₆Ge₄₀ predict the power function to be enhanced for a Fermi level located just below the top of the valence band. To explore the potential of Cu containing Ge clathrates as thermoelectric materials we have synthesized eight samples with nominal stoichiometry Ba₈Cu_6-xGe_40+x x = 0 - 0.7. This is an ongoing project and we present here some of our preliminary results for the x = 0.1 sample. Contradictory to expectation n-type behavior is observed in this sample. Furthermore, the thermoelectric properties are relatively poor, mainly due to the low mobility of the charge carriers that results in a high resistivity.