Composition dependence of glass transition temperature and fragility. I. A topological model incorporating temperature-dependent constraints

Gupta, Prabhat K.; Mauro, John C.

doi:10.1063/1.3077168

Cited by 294 publications

(349 citation statements)

References 78 publications

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“…More recently, temperature-dependent constraint theory has been used to calculate other macroscopic network properties such as the composition dependence of the glass transition temperature and liquid fragility (37)(38)(39). Fig.…”

Section: Discussionmentioning

confidence: 99%

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

Zeidler

Salmon

Skinner

2014

Proc. Natl. Acad. Sci. U.S.A.

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Liquid and glassy oxide materials play a vital role in multiple scientific and technological disciplines, but little is known about the part played by oxygen-oxygen interactions in the structural transformations that change their physical properties. Here we show that the coordination number of network-forming structural motifs, which play a key role in defining the topological ordering, can be rationalized in terms of the oxygen-packing fraction over an extensive pressure and temperature range. The result is a structural map for predicting the likely regimes of topological change for a range of oxide materials. This information can be used to forecast when changes may occur to the transport properties and compressibility of, e.g., fluids in planetary interiors, and is a prerequisite for the preparation of new materials following the principles of rational design. Examples range from the dependence on network connectivity of the transport properties (e.g., viscosity) of glass-forming and/or magma-related oxide melts (3-7) to the role played by atomic packing in determining the elastic behavior of glass (8-10). In the case of open glass-forming structures, the network connectivity often follows from Zachariasen's rules (11), but there is no reliable guide for predicting the conditions under which transformations occur in the character of network-forming motifs, e.g., from AO 3 to AO 4 or from AO 4 to AO 6 polyhedra.With increasing density, oxygen-oxygen interactions are expected to manifest themselves in the structural transformations that occur (12), but the nature of this role is unknown. For example, the oxygen atom number density ρ O will depend on the type of network-forming motifs, can be altered by adding network modifiers, and will increase with density. Nevertheless, a plot of ρ O versus the measured mean A-O coordination number n O A for network-forming structural motifs does not offer a basis for generalization (Fig. 1). It will be shown, however, that if the data are scaled by the volume occupied by an oxide ion V O , and an adjustment is made for the volume occupied by any network-modifying atoms (i.e., atoms other than oxygen that are not at the centers of network-forming motifs), then the resultant oxygenpacking fraction η O does offer a means for rationalizing the structural transformations that occur. An important proviso is that a constant oxide ion size cannot be assumed. Instead, the oxide ion environment has a profound influence as evidenced by the instability of these ions in the gas phase but their omnipresence in condensed matter (13,14). This variability was recognized in the construction of well-known tables of ionic radii (15, 16), although a constant size was assumed for a given oxide ion coordination number. The variability of the oxide ion size is also a key theme in the development of transferable aspherical ion models which have been successful in accounting for many of the structure-related properties of oxide materials (13,14). In the following we use an empirical approach to tac...

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Section: Discussionmentioning

confidence: 99%

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

Zeidler

Salmon

Skinner

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…8, full precision trend given in Fig. 8 caption, see also Melt fragility measures the degree of deviation from Arrhenian behavior of the liquid viscosity, and has been directly related to the temperature dependence of the number of degrees of freedom per atom [61][62][63]. Hence the observed temperature dependence of the coordination numbers is expected to contribute to an increased liquid fragility, as well as to the large thermal expansion coefficient (see Table III and Fig.…”

Section: Temperature Dependence Of the Liquid Structurementioning

confidence: 99%

Structure of molten titanium dioxide

et al. 2014

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The x-ray structure factor of molten TiO 2 has been measured for the first time, enabled by the use of aerodynamic levitation and laser beam heating, to a temperature of T = 2250(30) K. Ti-O coordination number in the melt is close to n TiO = 5.0(2), with modal Ti-O bond length r TiO = 1.881(5) Å, both values being significantly smaller than for the high temperature stable Rutile crystal structure (n TiO = 6.0, r TiO = 1.959 Å). The structural differences between melt and crystal are qualitatively similar to those for alumina, which is rationalized in terms of the similar field strengths of Ti 4+ and Al 3+. The diffraction data are used to generate physically and chemically reasonable structural models, which are then compared to the predictions based on various classical molecular dynamics (MD) potentials. New interatomic potentials, suitable for modelling molten TiO 2 , are introduced, given the inability of existing MD models to reproduce the diffraction data. These new potentials have the additional great advantage of being able to predict the density and thermal expansion of the melt, as well as solid amorphous TiO 2 , in agreement with published results. This is of critical importance given the strong correlation between density and structural parameters such as n TiO . The large thermal expansion of the melt is associated with weakly temperature dependent structural changes, whereby simulations show that n TiO = 5.85(2) -(3.0(1) x 10 -4 )T (K, 2.75 Å cut-off). The TiO 2 liquid is structurally analogous to the geophysically relevant high pressure liquid silica system at around 27 GPa. We argue that the predominance of 5-fold polyhedra in the melt implies the existence of as yet undiscovered TiO 2 polymorphs, based on lowerthan-octahedral coordination numbers, which are likely to be metastable under ambient conditions. Given the industrial importance of titanium oxides, experimental and computational searches for such polymorphs are well warranted.

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“…On the other hand, parameters such as the glass transition temperature, Tg, which are not so directly dependent on the atomic mass, can also be useful probes of changes in structural behaviour. For example, Fu et al [54] recently used topological constraint theory [55] to show that changes in Tg can be predicted based upon the number of terminal and non-bridging oxygens in the glass. Figure 8 shows Tg values published by Mochida et al for lithium, sodium, and potassium tellurite glasses [56].…”

Section: Implications For Models Of the Glass Networkmentioning

confidence: 99%

Alkali environments in tellurite glasses

Barney

Hannon

Holland

et al. 2015

Journal of Non-Crystalline Solids

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Neutron diffraction measurements are reported for five binary alkali tellurite glasses, xM2O·(100-x)TeO2 (containing 10 and 20 mol% K2O, 10 and 19 mol% Na2O, and 20 mol% 7 Li2O), together with 23 Na MAS NMR measurements for the sodium containing glasses.Differences between neutron correlation functions are used to extract information about the local environments of lithium and sodium. The Na-O bond length is 2.37(1) Å and the average Na-O coordination number, nNaO, decreases from 5.2(2) for x=10 mol% Na2O to 4.6(1) for x=19 mol% Na2O. The average Li-O coordination number, nLiO, is 3.9(1) for the glass with x=20 mol% Li2O and the Li-O bond length is 2.078(2) Å. As x increases from 10 to 19 mol% Na2O, the 23 Na MAS NMR peak moves downfield, confirming an earlier report of a correlation of peak position with sodium coordination number. The close agreement of the maximum in the Te-O bond distribution for sodium and potassium tellurite glasses of the same composition, coupled with the extraction of reasonable alkali coordination numbers using isostoichiometric differences, gives strong evidence that the tellurium environment in alkali tellurites is independent of the size of the modifier cation used.

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Composition dependence of glass transition temperature and fragility. I. A topological model incorporating temperature-dependent constraints

Cited by 294 publications

References 78 publications

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

Structure of molten titanium dioxide

Alkali environments in tellurite glasses

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