Crystal structure refinement of a type-I clathrate compound Ba8Ge43 with an ordered arrangement of germanium vacancies

The crystal structure of a type-I clathrate compound Ba8Ge43 with an ordered arrangement of vacancies has been investigated by synchrotron X-ray diffraction. Ba8Ge43 possesses a large cubic unit cell with a lattice parameter twice that of the usual type-I clathrate structure due to an ordered arrangement of Ge vacancies. The space group is Ia3d. , which is different from that of the usual type-I clathrate structure (Pm3n). Ge vacancies occupy exclusively the 24c sites, which correspond to half the 6c sites in the usual parent type-I clathrate structure. The atomic coordinates and isotropic atomic displacement parameters for the Ba and Ge atoms are determined through Rietveld refinement with synchrotron X-ray data.