Structure of germanium-selenium glasses: An x-ray-absorption fine-structure study

X-ray-absorption fine-structure (XAFS) data in the binary chalcogenide glass system ${\mathrm{Ge}}_{\mathit{x}}$ ${\mathrm{Se}}_{100\mathrm{-}\mathit{x}}$ system are presented and discussed. Phase-corrected Fourier transforms in a curved-wave XAFS simulation formalism are employed in analysis of the data, and near-edge structures are compared for the various compositions studied. Analysis of the XAFS data confirms the presence of chemical ordering. Least-squares-fitting results show that short-range order in the first shell is well preserved throughout the composition range studied. The coordination numbers for germanium and selenium (4 and 2, respectively) are unchanged for the composition 20≤x≤40. For x≤33, there exist stable tetrahedral Ge(${\mathrm{Se}}_{1/2}$ ${)}_4$ units that are connected by either double or single selenium atoms. For x>33, Ge-Ge bonds appear, and the structure becomes more disordered compared to that of glassy ${\mathrm{GeSe}}_2$.