A Neutron Diffraction Study of the Thermal Stability of the α-Quartz-Type Structure in Germanium Dioxide

Haines, J.; Cambon, O.; Philippot, E.; Chapon, L. C.; Hull, S.

doi:10.1006/jssc.2002.9625

Cited by 100 publications

(127 citation statements)

References 31 publications

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“…The high temperature (up to 1344 K) behaviour of this polymorph has been investigated by Haines et al [29] who found that the intertetrahedral bridging angle (Ge − O − Ge) and tilt angles exhibit thermal stabilities that are amongst the highest observed for quartz-type analogues. With increasing temperature, expansion of the unit cell is highly anisotropic with expansion along a being 5 times greater than along c [29].…”

Section: High Pressure and Temperature Behaviourmentioning

confidence: 96%

The structure of amorphous, crystalline and liquid GeO₂

Micoulaut

Cormier

Henderson

2006

J. Phys.: Condens. Matter

228

256

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Abstract. Germanium dioxide (GeO 2 ) is a chemical analogue of SiO 2 . Furthermore, it is also to some extent a structural analogue, as the low and high-pressure short-range order (tetrahedral and octahedral) is the same. However, a number of differences exist. For example, the GeO 2 phase diagram exhibits a smaller number of polymorphs, and all three GeO 2 phases (crystalline, glass, liquid) have an increased sensitivity to pressure, undergoing pressure induced changes at much lower pressures than their equivalent SiO 2 analogues. In addition, differences exist in GeO 2 glass in the medium range order, resulting in the glass transition temperature of germania being much lower than for silica. This review highlights the structure of amorphous GeO 2 by different experimental (e.g., Raman and NMR spectroscopy, neutron and x-ray diffraction) and theoretical methods (e.g., classical molecular dynamics, ab initio calculations). It also addresses the structure of liquid and crystalline GeO 2 that have received much less attention. Furthermore, we compare and contrast the structural differences between GeO 2 and SiO 2 , as well as, along the GeO 2 − SiO 2 join. It is probably a very timely review as interest in this compound, that can be investigated in the liquid state at relatively low temperatures and pressures, continues to increase.

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Section: High Pressure and Temperature Behaviourmentioning

confidence: 96%

The structure of amorphous, crystalline and liquid GeO₂

Micoulaut

Cormier

Henderson

2006

J. Phys.: Condens. Matter

228

256

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“…ref. [32]), and also between the mean Ge-O length and θ in GeO 2 α-quartz [37]. Hence two deformation mechanisms acting in opposite senses to each other are known in these polymorphs.…”

Section: Poisson's Ratios Of the Undeformed Silica And Germania Polymmentioning

confidence: 96%

“…dsecθ/dR relates the amount of intertetrahedral angle change (θ = M-O-M angle) to the change in size of a tetrahedron and is related to the inter-and intratetrahedral forces. Both polymorphs contain tetrahedra of similar size (see above) and have similar intertetrahedral angles (θ ~ 144.4 and 146.4° for silica α-quartz [35] and silica α-cristobalite [36], respectively and 130° and 128° respectively for germania [33,34]) and intertetrahedral distances (Si…Si distance ~ 3.06Å for the silica polymorphs [32,33]; Ge…Ge distance ~ 3.15Å for the germania polymorphs [37]). Therefore, to a first approximation we expect the inter-and intra-tetrahedral forces to yield similar values of dsecθ/dR for both polymorphs if the CTM is valid.…”

Section: Poisson's Ratios Of the Undeformed Silica And Germania Polymmentioning

confidence: 99%

Deformation mechanisms leading to auxetic behaviour in the α-cristobalite and α-quartz structures of both silica and germania

Alderson¹,

Evans²

2008

J. Phys.: Condens. Matter

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Analytical expressions have been developed in which the elastic behaviour of the α-quartz and α-cristobalite molecular tetrahedral frameworks of both silica and germania are modelled by rotation, or dilation or concurrent rotation and dilation of the tetrahedra. Rotation and dilation of the tetrahedra both produce negative Poisson’s ratios (auxetic behaviour), whereas both positive and negative values are possible when these mechanisms act concurrently. Concurrent rotation and dilation of the tetrahedra reproduces with remarkable accuracy both the positive and negative ν31 Poisson’s ratios observed for silica α-quartz and α-cristobalite, respectively, when loaded in the x3 direction. A parametric fit of the concurrent model to the germania α-quartz experimental ν31 Poisson’s ratio is used to predict ν31 for germania α-cristobalite, for which no experimental value exists. This is predicted to be +0.007. Strain-dependent ν31 trends, due to concurrent rotation and dilation in the silica structures, are in broad agreement with those predicted from pair-potential calculations, although significant differences do occur in the absolute values. With the model of concurrent dilation and rotation of the tetrahedra we predict that an alternative uniaxial stress (σ3)-induced phase exists for both silica, α-quartz and α-cristobalite, and germania, α-cristobalite, having geometries in reasonable agreement with β-quartz and idealized β-cristobalite, respectively.

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“…Using r 4 of 1.737 Å in quartz-type GeO 2 (Haines et al, 2002) and r 6 of 1.885 Å in rutile-type GeO 2 (Bolzan et al, 1997), the value of N 6 increases approximately 20% in the composition range of 0-24 mol% Li 2 O. Although a small discrepancy in the total fraction of the GeO 6 unit obtained by the addition of the LiO 2 component can be observed between the results of AXS and EXAFS, the present study stresses that the fraction of the GeO 6 unit in the lithium-germanate glasses increases with increasing Li 2 O content up to 24 mol% and the amount of GeO 6 is proportional to Li 2 O content.…”

Section: Resultsmentioning

confidence: 99%

Local structure around Ge in lithium germanate glasses analyzed by AXS and EXAFS techniques

Arima

Kawamata

Sugiyama

2015

Journal of Mineralogical and Petrological Sciences

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A Neutron Diffraction Study of the Thermal Stability of the α-Quartz-Type Structure in Germanium Dioxide

Cited by 100 publications

References 31 publications

The structure of amorphous, crystalline and liquid GeO₂

The structure of amorphous, crystalline and liquid GeO₂

Deformation mechanisms leading to auxetic behaviour in the α-cristobalite and α-quartz structures of both silica and germania

Local structure around Ge in lithium germanate glasses analyzed by AXS and EXAFS techniques

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A Neutron Diffraction Study of the Thermal Stability of the α-Quartz-Type Structure in Germanium Dioxide

Cited by 100 publications

References 31 publications

The structure of amorphous, crystalline and liquid GeO2

The structure of amorphous, crystalline and liquid GeO2

Deformation mechanisms leading to auxetic behaviour in the α-cristobalite and α-quartz structures of both silica and germania

Local structure around Ge in lithium germanate glasses analyzed by AXS and EXAFS techniques

Contact Info

Product

Resources

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The structure of amorphous, crystalline and liquid GeO₂

The structure of amorphous, crystalline and liquid GeO₂