A new clathrate phase with the composition Ge40.0Te5.3I8 has been prepared and its structure determined from single crystal X-ray data. It crystallizes in the cubic space group Pm-3n with unit cell parameter a = 10.815(1) Å and Z = 1 (R = 0.031 for 272 independent reflections and 19 variables). Germanium and tellurium form a cationic clathrate framework hosting the guest iodine anions in cages of two different shapes. The cationic framework features a joint occupation on two of the three independent sites by germanium and tellurium, leading to the formation of Ge—Ge and Ge—Te bonds and vacancies on the third position. Electron diffraction and high-resolution electron microscopy reveal that the bulk material is not uniform; it contains domains showing a tendency for segregation of tellurium and germanium within the 4-fold positions of the space group P23, which is a subgroup of Pm-3n. Ge40.0Te5.3I8 is a diamagnetic semiconductor with a band gap of about 0.8 eV and its composition agrees with the Zintl formalism for the charge-balanced compounds.
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