Unusual Solid Solutions in the System Ge-Sb-Te: The Crystal Structure of 33R-Ge4-xSb2-yTe7 (x, y ≈ 0.1) is Isostructural to that of Ge3Sb2Te6

Whereas for a Series Of layered compounds with the general formula (GeTe)(n)(Sb-2 Te-3)(m) the stoichiometry allows to predict the Structure type and the average thickness of the hexagonal atom layers. these rules are not generally applicable tor Ge-Te-rich compounds like Ge4Sb2Te7. A 39R layer stacking is expected, however, single crystal diffraction studies reveal a 33R layered Structure (R (3) over tildem, a = 4.1891(5) angstrom, c = 62.169(15), R = 0.047) closely related to that Of Ge3Sb2Tc6. This is also corroborated by the average layer thickness that can be determined from the strong reflections or powder patterns and exhibits a direct relation to the structure type. Mixed occupancy of cation positions with Ge and Sb and possibly defects allow this unusual range of homogeneity. Bulk material of the kinetically stable compound can be synthesized by quenching stoichiometric melts of the pure elements and subsequent annealing.