Vibrational densities of states and network rigidity in chalcogenide glasses

Wa, Kamitakahara; Rl, Cappelletti; Boolchand, P.; Halfpap, B. L.; Gompf, F.; Da, Neumann; Mutka, H.

doi:10.1103/physrevb.44.94

Cited by 154 publications

(121 citation statements)

References 13 publications

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“…The iteration terminates when numerical convergence of S 1 (Q, E) is achieved. Best agreement of the bulk VDoS measured by IXS and inelastic neutron-scattering experiments 19,20 is achieved for an elastic peak contribution of a 0 = 0.6, see Figure 3.…”

Section: Methodsmentioning

confidence: 76%

“…The VDoS were determined under the incoherent approximation using the structural factors at all available values of Q, assuming that single-phonon scattering is predominant. The comparison between the VDoS determined by IXS and inelastic neutron-scattering experiments 19,20 and molecular dynamics simulations 21 is shown in Figure 3 for bulk glassy Se. A good agreement has been achieved by selecting an elastic peak contribution of ~60%.…”

Section: Experimental Vdos For Bulk and Surface-sensitive Geometriesmentioning

confidence: 99%

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Vibrational dynamics and surface structure of amorphous selenium

et al. 2011

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In contrast to crystalline solids in which structural order governs dynamics and thermodynamics, the lack of long-range periodicity in amorphous materials is responsible for several anomalies. Although the relation between these anomalies and the 'bulk structure' is generally understood, the surface structure and the corresponding vibrational spectrum of amorphous solids is practically an unexplored theme. In this study, we resolve the differences in vibrational dynamics and atomic structure between bulk and surface (top 5 nm) atoms of amorphous selenium. We combine experimental (grazing incidence inelastic X-ray scattering) and computational (ab initio and semiempirical molecular orbital theoretical calculations) methods to scrutinize a variety of possible structural models. We find that a high concentration of particular types of 'coordination defects' in the surface layer is responsible for the observed differences. Resolving the structure of amorphous surfaces is, for example, important for understanding nanoparticles' properties where the surface-to-bulk ratio has a crucial role.

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Section: Methodsmentioning

confidence: 76%

Section: Experimental Vdos For Bulk and Surface-sensitive Geometriesmentioning

confidence: 99%

Vibrational dynamics and surface structure of amorphous selenium

et al. 2011

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“…4e) actually has a deeper meaning. It corresponds to the well-known Maxwell stability criterion 5,6 of isostatic structures 17 , and has been identified in glasses as the location of a mean-field rigidity transition 17,18 , which separates and n c BB , we now realize that with the pressure-imposed coordination change leading to a growth of network connectivity and stretching interactions (n c BS ), the energetically weaker interactions (BB) 22 soften to accommodate the increase of stress. The angular adaptation reducing n c BB (as sketched in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…5b and black curve Fig. 5c), corresponding to frequencies of about 1.25-2 THz (5-8 meV), that is, to frequencies that are typical of floppy modes 22 . These features are virtually absent in isostatic and stressed rigid systems, or are, at least, substantially reduced.…”

Section: Discussionmentioning

confidence: 99%

Densified network glasses and liquids with thermodynamically reversible and structurally adaptive behaviour

2015

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If crystallization can be avoided during cooling, a liquid will display a substantial increase of its viscosity, and will form a glass that behaves as a solid with a relaxation time that grows exponentially with decreasing temperature. Given this 'off-equilibrium' nature, a hysteresis loop appears when a cooling/heating cycle is performed across the glass transition. Here we report on molecular dynamics simulations of densified glass-forming liquids that follow this kind of cycle. Over a finite pressure interval, minuscule thermal changes are found, revealing glasses of 'thermally reversible' character with optimal volumetric or enthalpic recovery. By analysing the topology of the atomic network structure, we find that corresponding liquids adapt under the pressure-induced increasing stress by experiencing larger bond-angle excursions. The analysis of the dynamic behaviour reveals that the structural relaxation time is substantially reduced in these adaptive liquids, and also drives the reversible character of the glass transition. Ultimately, the results substantiate the notion of stress-free (Maxwell isostatic) rigidity in disordered molecular systems, while also revealing new implications for the topological engineering of complex materials.

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“…3 For instance, in multicomponent chalcogenide glasses containing an important fraction of Group VI elements (S, Se, Te) or in multicomponent oxides, such rules permit determining the fl exible-torigid transition due to the presence of anomalies or thresholds in various physicochemical properties, as detected from Raman scattering, 5 stress relaxation and viscosity measurements, 6 vibrational density of states, 7 Brillouin scattering, 8 and resistivity. 9 However, for many other systems, including the important classes of oxides, silicates, or borosilicates, which represent the base material for many domestic and industrial applications in glass science, the question of a well-defi ned coordination number has been a long-standing issue.…”

Section: Matthieu Micoulaut and Yuanzheng Yue Guest Editorsmentioning

confidence: 99%