Unexpected Ge-Ge Contacts in the Two-Dimensional Ge4 Se3 Te Phase and Analysis of Their Chemical Cause with the Density of Energy (DOE) Function

Abstract

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 Ge₄ Se₃ 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 Ge₄ Se₃ 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.

Keywords: DOE; X-ray diffraction; ab initio calculations; chalcogenides; solid-state structures.