Unexpected Ge-Ge contacts in the two-dimensional Ge₄Se₃Te phase and analysis of their chemical cause with the density of energy (DOE) function

A hexagonal phase in the ternary Ge-Se-Te system with an approximate composition of GeSe_0.75Te_0.25 has been known since the 1960s but its structure has remained unknown. We have succeeded in growing single crystals by chemical transport as a prerequisite to solve and refine the Ge₄Se₃Te structure. It consists of layers that are held together by van der Waals type weak chalcogenide-chalcogenide interactions but also display unexpected Ge-Ge contacts, as confirmed by electron microscopy analysis. The nature of the electronic structure of Ge₄Se₃Te was characterized by chemical bonding analysis, in particular by the newly introduced density of energy (DOE) function. The Ge-Ge bonding interactions serve to hold electrons that would otherwise go into antibonding Ge-Te contacts. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)