Structural relationships of BaGe5 to clathrate I and II

Abstract

Abstract The orthorhombic phase BaGe5 (Pearson symbol oP60; also called Ba10Ge50) was resolved by crystal chemical analogy and was found to be related to the cubic clathrate II. An orthorhombic structure model for BaGe5 was obtained from a cluster-filled clathrate II derivative. The structure refinement (Rietveld method), based on X-ray diffraction powder data, resulted in a defect-rich clathrate II structure with Ba and Ge vacancies. Further analysis shows that BaGe5 can be derived from the clathrate I Ba8Ge43 by constructive crystallographic shear. The relationship to clathrate IX Ba6Ge25 is also discussed.