Raman scattering and local order in GexSe 1 -x glasses for 1/3 ≤ x ≤ 1/2

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Abstract
Having previously studied the local order of GexSe1-x glasses between pure selenium and x = 1/3, we have now prepared samples for 1/3 ≤ x ≤ 1/2. Glassy materials have been obtained up to x = 0.44 and, at higher x values, the samples are made of GeSe crystallites embedded in a glassy matrix of GexSe1-x, with x = 0.41 ± 0.01, the percentage of glass going to zero when x goes to 1/2. Raman scattering measurements have been performed on a set of such samples, at room temperature. The results lead to the following model of local order : for 1/3 ≤ x ≤ 0.42, the glasses have a GeSe2-like local order with four-coordinated Ge atoms and two-coordinated Se atoms, Se—Se bonds and two Ge—Ge bonds per Ge atom being statistically forbidden; for x ≽ 0.43 strong indications appear for a GeSe-like local order, with both three-coordinated Ge and Se atoms : such a type of coordination has never been previously reported for glasses