Host-guest coupling in semiconducting Ba8Zn8Ge38

Two samples of the type I clathrate Ba8Zn8Ge38 have been prepared by a self-flux method with different cooling rates. Transport properties have been measured for a large single crystal of Ba8Zn8Ge38 from the slow cooled batch, and they reveal the sample to be semiconducting. A high Seebeck coefficient of -175 mu V K-1 was observed at 400 K. High resolution single crystal neutron diffraction data measured for both slow cooled and fast cooled samples reveal significant differences in the guest atom nuclear density, which can be related to the occupancies of Zn in the host structure framework. Analysis of the atomic displacement parameters shows that the Einstein temperatures of the barium guest atoms are of comparable size at 62 and 67 K for the slow and fast cooled samples, respectively. The Debye temperature for the host framework was in both cases found to be similar to 280 K.