Structural features of Ge1Sb4Te7, an intermetallic compound in the GeTe-Sb2Te3 homologous series

The structural and bonding, nature of Ge1Sb4Te7 is investigated using an X-ray diffraction method and calculations based on density-functional theory (DFT). This material's crystal is confirmed to have a 12-layered, close-packed cubic stacking structure (P (3) over bar ml). In this crystal, Te atoms occupy their own specific layers; however, it has been revealed that Ge and Sb atoms are not located in their respective layers but cause partial atomic disordering across other layers. The structure consists of two kinds of NaCl slabs stacked alternately, and the calculations demonstrate that adjacent slabs are connected by a van der Waals-type weak force and that Ge1Sb4Te7 forms a compound semiconductor with a very narrow band gap.