Short-range structure and chemical order in In-Ge sulfide and selenide glasses by X-ray absorption fine structure spectroscopy

The nearest-neighbor coordination environments of In and Ge atoms in In-Ge sulfide and selenide glasses have been studied with In and Ge K-edge EXAFS spectroscopy. The Ge atoms are coordinated to 4 S (Se) atoms in all sulfide (selenide) glasses. The In atoms are found to be present in the In3+ state and are tetrahedrally coordinated by 4 S nearest neighbors in the S-excess glass and ∼3.6 S + ∼ 0.4 Ge neighbors in the stoichiometric and S-deficient glass. These results imply a two coordinated state for the S atoms and preservation of chemical order in all glasses. The In atoms in a stoichiometric selenide glass are found to be coordinated to 4 Se nearest neighbors, although possible partial contribution from Ge nearest neighbors similar to that observed in the case of sulfides can not be disregarded.