Structure, Connectivity, and Configurational Entropy of GexSe100−x Glasses: Results from 77Se MAS NMR Spectroscopy

High-resolution 77 Se MAS NMR spectroscopy has been conducted at 11.7 T to investigate the short-and intermediate- range structure and chemical order in binary Ge x Se 100− x glasses with 5 ≤ x ≤ 33.33. Four distinct Se environments are observed for the first time, corresponding to Se− Se −Se and Ge− Se −Se linkages as well as Ge− Se −Ge sites where the Se atom is shared by two GeSe 4 tetrahedra in either corner-sharing or edge-sharing configuration. Assignments of corner and edge-shared tetrahedra were made based on the 77 Se MAS NMR spectrum of crystalline β-GeSe 2 . Analysis of the compositional variation of the relative concentrations of these Se sites indicates that the structure of Ge x Se 100− x glasses in this composition range can be described as a randomly interconnected network of GeSe 4 tetrahedra and chains of Se atoms. The implications of this structural model are discussed in relation to the composition dependence of the glass-forming ability and kinetic fragility of the corresponding parent liquids.