Glass Formation at the Limit of Insufficient Network Formers

Kohara, Shinji; Suzuya, Kentaro; Takeuchi, Ken; Loong, C.‐K.; Grimsditch, M.; Weber, Jacques; Tangeman, Jean A.; Key, Thomas S.

doi:10.1126/science.1095047

Cited by 176 publications

(160 citation statements)

References 16 publications

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“…Similarly there are differences in the heat of vitrification [19]. These observations imply a correlation between changes in the bulk thermodynamic properties (enthalpy, entropy and volume) at the limit of network glass formation suggested by Kohara [23].…”

Section: The Structure Of Mgo-sio 2 Liquidsmentioning

confidence: 92%

“…A comparison of the real space data for the glassy state can be used as a starting point in interpretation of the liquid structures [23]. In the pair-distribution function (PDF) there are three major peaks.…”

Section: Resultsmentioning

confidence: 99%

“…In MgOSiO 2 glasses there is an increase in area of the Mg-O correlation at 2.0 Å in the glasses between 38% and 33% SiO 2 an increase in coordination number from 4.5 to 5.0 [17,18]. Kohara [23] has used combined neutron and highenergy diffraction data in reverse Monte Carlo models of the 33% SiO 2 (forsterite) glass structure to suggest that Mg-O forms a distorted MgO n (n = 4, 5, 6) polyhedron edge shared with other Mg-O polyhedra to form a percolation domain. Liquid II is the liquid form of this glass.…”

Section: The Structure Of Mgo-sio 2 Liquidsmentioning

confidence: 99%

“…The more silica-rich glasses, with 38-50 mole% SiO 2 are stronger. The structure of the forsterite composition glass also differs from those that are more SiO 2 -rich, the mean coordination number for forsterite glass is 5.0 compared with 4.5 for the 38-50% SiO 2 compositions [17,23]. This increase in Mg-O coordination represents a change in the structural role of the silicate tetrahedron, it has been argued by Kohara that forsterite composition glasses (33% SiO 2 ) represent the limit to the formation of a polymerised network of corner-shared SiO 4 tetrahedra and that the increase in Mg-O coordination number reflects formation of a network for edge-and faceshared Mg-O polyhedra corner-shared with isolated SiO 4 tetrahedra and Si 2 O 7 dimers.…”

Section: Introductionmentioning

confidence: 99%

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In situ diffraction studies of magnesium silicate liquids

2008

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Primitive MgO-SiO 2 liquids dominate the early history of the Earth and Terrestrial planets. The structures of these liquids and structure-dependent properties, such as viscosity and diffusion, are considered important in the evolution of these planets, however, MgO-SiO 2 liquids are refractory and do not form glasses easily and it is difficult to measure the structure of these liquids. Container-less synthesis techniques have been used to produce glasses that range in composition from 50 to 33% SiO 2 , corresponding to the compositions of two important mantle minerals: enstatite and forsterite. The structure of these glasses has been determined using combined neutron and high-energy diffraction and show changes in the short-range order as a function of composition. These changes include a jump in Mg-O coordination number at the limit to the formation of the silicate network in forsterite composition glass. These results imply a similar change in the structure of the liquid. Accordingly, the structures of forsterite and enstatite liquids have been determined using high-energy X-rays and a specialized sample environment, a containerless levitator. The main qualitative structural differences between MgSiO 3 and Mg 2 SiO 4 glasses are also observed in the melt. Liquid MgSiO 3 is interpreted as forming a relatively 'strong' network of SiO 4 tetrahedra, whereas the Mg 2 SiO 4 liquid is ''fragile'' and dominated MgO n (n = 4, 5, 6) polyhedra and highly mobile oxygen ions. The results differ significantly from previously reported X-ray diffraction data for liquid MgSiO 3 .

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Section: The Structure Of Mgo-sio 2 Liquidsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Section: The Structure Of Mgo-sio 2 Liquidsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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In situ diffraction studies of magnesium silicate liquids

2008

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“…For this and other reasons, thermal and vibrational properties in amorphous materials have long been a source of controversy [1][2][3] . However, recently, some progress has been achieved for the 'bulk structure' [4][5][6] . Vibrational excitations at ordered surfaces have methodically been studied for several decades, both experimentally and theoretically 7 .…”

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confidence: 99%

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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Control of Liquid Properties and Structure Via Melt Chemistry

Weber¹

2006

Ceramic Transactions Series

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Glass Formation at the Limit of Insufficient Network Formers

Cited by 176 publications

References 16 publications

In situ diffraction studies of magnesium silicate liquids

In situ diffraction studies of magnesium silicate liquids

Vibrational dynamics and surface structure of amorphous selenium

Control of Liquid Properties and Structure Via Melt Chemistry

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