Germanium selenide glass structures studied by 77Se solid state NMR and mass spectroscopy

Bureau, Bruno; Troles, Johann; Floch, Marie Le; Guénot, Pierre; Smektala, F.; Lucas, Jacques

doi:10.1016/s0022-3093(02)01911-7

Cited by 60 publications

(96 citation statements)

References 19 publications

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“…The majority of intertetrahedral connections are, however, formed from Se n bridges where n is an integer 2. These findings are consistent with previous FPMD simulations on GeSe 4 glass at ambient pressure [59,60] and indicate the absence of a network that is phase separated on the nanoscale into GeSe 2 fragments and Se n chains, a scenario that would be accompanied by a small proportion of AB configurations and by large proportions of both AA and BB configurations [16,21]. The FPMD models find a broad distribution of chain lengths as indicated by Fig.…”

Section: Discussionsupporting

confidence: 91%

Pressure-induced structural changes in the network-forming isostatic glassGeSe4: An investigation by neutron diffraction and first-principles molecular dynamics

et al. 2016

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The changes to the topological and chemical ordering in the network-forming isostatic glass GeSe 4 are investigated at pressures up to ∼14.4 GPa by using a combination of neutron diffraction and first-principles molecular dynamics. The results show a network built from corner-and edge-sharing Ge(Se 1/2 ) 4 tetrahedra, where linkages by Se 2 dimers or longer Se n chains are prevalent. These linkages confer the network with a local flexibility that helps to retain the network connectivity at pressures up to ∼8 GPa, corresponding to a density increase of ∼37%. The network reorganization at constant topology maintains a mean coordination number n 2.4, the value expected from mean-field constraint-counting theory for a rigid stress-free network. Isostatic networks may therefore remain optimally constrained to avoid stress and retain their favorable glass-forming ability over a large density range. As the pressure is increased to around 13 GPa, corresponding to a density increase of ∼49%, Ge(Se 1/2 ) 4 tetrahedra remain as the predominant structural motifs, but there is an appearance of 5-fold coordinated Ge atoms and homopolar Ge-Ge bonds that accompany an increase in the fraction of 3-fold coordinated Se atoms. The band gap energy decreases with increasing pressure, and midgap states appear at pressures beyond ∼6.7 GPa. The latter originate from undercoordinated Se atoms that terminate broken Se n chains.

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Section: Discussionsupporting

confidence: 91%

Pressure-induced structural changes in the network-forming isostatic glassGeSe4: An investigation by neutron diffraction and first-principles molecular dynamics

et al. 2016

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“…To investigate this possibility, the MYEGA model (Mauro et al, 2009) FIGURE 4 | The dependence of the glass transition temperature Tg for the GexSe 1− x system, as measured using a variety of methods, on the composition x and mean coordination numbern = 2(1 + x). The results obtained from the total heat flow in the present work are compared to the results obtained by Avetikyan and Baidakov (1972), Awasthi and Sampath (2002), Azoulay et al (1975), Bhosle et al (2012a,b), Boolchand (2000), Boolchand and Bresser (2000), Bureau et al (2003), Dembovskii et al (1965), Feltz and Lippmann (1973), Feltz et al (1983), Feng et al (1997, Gueguen et al (2011), Guin et al (2002a, Gulbiten et al (2013), Lucas et al (2003), Nemilov (1964), Ota et al (1978), Sarrach et al (1976), Senapati and Varshneya (1996), Sharma et al (2005), Sreeram et al (1991a), Svoboda and Málek (2015), Wagner et al (1997), Wang et al (2005), Yang et al (2013), and Zhao et al (2013). The inset shows solely the results for Tg,rev as obtained in the present work and in the work of Boolchand and coworkers (Feng et al, 1997;Boolchand, 2000;Boolchand and Bresser, 2000;Wang et al, 2005;Bhosle et al, 2012a,b)-see Section 3.1 for details.…”

Section: Viscosity and Fragility Indexsupporting

confidence: 57%

Topological Ordering and Viscosity in the Glass-Forming Ge–Se System: The Search for a Structural or Dynamical Signature of the Intermediate Phase

et al. 2017

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The topological ordering of the network structure in vitreous Ge x Se 1−x was investigated across most of the glass-forming region (0 ≤ x ≤ 0.4) by using high-resolution neutron diffraction to measure the Bhatia-Thornton number-number partial structure factor. This approach gives access to the composition dependence of the mean coordination number n and correlation lengths associated with the network ordering. The thermal properties of the samples were also measured by using temperature-modulated differential scanning calorimetry. The results do not point to a structural origin of the so-called intermediate phase, which in our work is indicated for the composition range 0.175(8) ≤ x ≤ 0.235(8) by a vanishingly small non-reversing enthalpy near the glass transition. The midpoint of this range coincides with the mean-field expectation of a floppy-to-rigid transition at x = 0.20. The composition dependence of the liquid viscosity, as taken from the literature, was also investigated to look for a dynamical origin of the intermediate phase, using the Mauro-YueEllison-Gupta-Allan (MYEGA) model to estimate the viscosity at the liquidus temperature. The evidence points to a maximum in the viscosity at the liquidus temperature, and a minimum in the fragility index, for the range 0.20 ≤ x ≤ 0.22. The utility of the intermediate phase as a predictor of the material properties in network glass-forming systems is discussed.

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“…The sealed silica tube was introduced into a rocking furnace and kept at 1023 K during 12 h to ensure a good mixing and homogenization of the liquid. The temperature was subsequently reduced to 923 K and staid constant for 1 h to reduce the gas pressure in the tube 3,12,13 . The obtained glass melt was then quenched in water (293 K) and annealed at T g during 4 h to reduce the residual stresses resulting from the cooling.…”

Section: A Materialsmentioning

confidence: 99%

“…The structure of these glasses might be slightly more complicated though, as will be further discussed, with Se occurring in at least three different sites 11 and possible "clustering" -at the scale of the structural units 12,13 . 77 Se experimental solid state Nuclear Magnetic Resonance and Raman scattering investigations have suggested a bimodal phase network, where the glass structure is composed of intertwined GeSe 2 and Se n microdomains 14 .…”

Section: Introductionmentioning

confidence: 99%

High-temperature elasticity and viscosity of GexSe1−xglasses in the transition range

et al. 2011

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Submitted to PRB July 14, 2010, revised Corresponding Author: Tanguy RouxelProfessor Tel: + 33-2-23236718Fax: + 33-2-23236111 E-mail: tanguy.rouxel@univ-rennes1.frThe viscous flow behavior and the temperature dependence of the elastic moduli of chalcogenide glasses from the germanium-selenium system were studied by means of homemade high temperature indentation setup and resonant frequency technique (1-10 kHz) respectively for temperatures between 0.8 and 1.2xT g . The softening rates, both in the elastic and in the viscous flow regimes, were correlated to network de-structuration or reorganization events in the light of previously reported high temperature neutron scattering data. The concomitant change of Poisson's ratio () and the thermodynamics parameters of the thermally activated viscous flow process, were characterized and provide a new basis for the understanding of the sources for the softening in the transition range. The temperature dependence of  suggests weak changes of the network cross-linking degree at large Gecontents. On the contrary, in the case of a-Se a steep fragmentation of the structural units is inferred from the (T) data and the flow process is accompanied by a huge entropy change (activation entropy at saddle point). The entropy contribution at T g (T g xS a ) represents more than 50 % of the activation enthalpy for flow (H a ) and increases with the selenium content.Hence the free activation energy (G a ) is much smaller than apparent activation energy as derived from viscosity data.

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Germanium selenide glass structures studied by 77Se solid state NMR and mass spectroscopy

Cited by 60 publications

References 19 publications

Pressure-induced structural changes in the network-forming isostatic glassGeSe4: An investigation by neutron diffraction and first-principles molecular dynamics

Pressure-induced structural changes in the network-forming isostatic glassGeSe4: An investigation by neutron diffraction and first-principles molecular dynamics

Topological Ordering and Viscosity in the Glass-Forming Ge–Se System: The Search for a Structural or Dynamical Signature of the Intermediate Phase

High-temperature elasticity and viscosity of GexSe1−xglasses in the transition range

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