Unexpected Ge-Ge Contacts in the Two-Dimensional Ge 4 Se 3 Te 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 _0.75 Te _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 Ge ₄ Se ₃ Te 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 Ge ₄ Se ₃ Te 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.
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