Crystal structure refinement of a type-I clathrate compound Ba 8Ge 43 with an ordered arrangement of germanium vacancies

Abstract

The crystal structure of a type-I clathrate compound Ba 8Ge 43 with an ordered arrangement of vacancies has been investigated by synchrotron X-ray diffraction. Ba 8Ge 43 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 Ia 3 ¯ d , which is different from that of the usual type-I clathrate structure ( Pm 3 ¯ n ) . 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.