Single crystals belonging to a new modification of GeSe2 have been prepared by several methods. This new form appears orthorhombic with parameters a = 7.037 -+_ 0-30, b = 11.826 ± 0.010, c = 16.821 ± 0.040/~ and z= 16. The measured density is 4.35+ 0.040 g cm -3. The space group has not yet been determined because cutting thin X-ray samples from large as-grown crystals induces considerable cleavage.
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
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