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High-frequency dynamics of vitreous GeSe2 (Articolo in rivista)

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Orsingher, Laura; Baldi, Giacomo; Fontana, Aldo; Bove, Livia Eleonora; Unruh, Tobias; Orecchini, Andrea; Petrillo, Caterina; Violini, Nicolo; Sacchetti, Francesco (2010)
High-frequency dynamics of vitreous GeSe2
in Physical review. B, Condensed matter and materials physics; American Physical Society (APS), College Pk (Stati Uniti d'America)
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Orsingher, Laura; Baldi, Giacomo; Fontana, Aldo; Bove, Livia Eleonora; Unruh, Tobias; Orecchini, Andrea; Petrillo, Caterina; Violini, Nicolo; Sacchetti, Francesco (literal)

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O.L., F.A.: Univ Trento, Dept Phys, I-38050 Trento, Italy; B.G., F.A.: UOS Roma, IPCF CNR, I-00185 Rome, Italy; B.G.: European Synchrotron Radiat Facil, F-38043 Grenoble, France; B.L.E. : Univ Paris 06, DPMD IMPMC, UMR 7590, F-75015 Paris, France; U.T. : Tech Univ Munich, Forsch Neutronenquelle Heinz Maier Leibnitz FRM 2, D-85747 Garching, Germany; O.A., P.C., V.N., S.F.: Univ Perugia, Dept Phys, I-06100 Perugia, Italy. (literal)

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The vibrational dynamics of vitreous germanium diselenide ?v-GeSe2?, an amorphous glass belonging to the family of continuous random network forming glasses, has been investigated by means of inelastic neutron scattering. We employed three different neutron spectrometers, each of them providing different energy resolutions and spanning different portions of the energy-wave-vector ???,Q? plane, which partially overlap so that complementary information can be obtained. Two well-defined peaks are resolved in the dynamic structure factor in a broad Q region, below and above the position of the first sharp diffraction peak in the static structure factor. The low-lying excitation is nondispersive and located around the boson peak frequency. The highfrequency mode presents a pseudoperiodic behavior and it can be associated to the high-frequency counterpart of the longitudinal acoustic ?LA? mode. In the low-Q region this mode shows a positive dispersion of its apparent sound velocity and an attenuation which follows a Q2 law. The combined use of a set of appropriate instruments allows an accurate determination of the nonergodicity parameter f?Q?. The LA dispersion curve of v-GeSe2 is similar to that measured in other glasses where a second excitation appears in the spectra. On the contrary other glass forming materials, where this second mode is not detected, present a sinusoidal-like dispersion curve with a deeper minimum in the second pseudo-Brillouin zone. (literal)

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