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    I.Fragility and its Relation to Other Glass Properties

    II.Networks

    Reinhard Conradt

    April 6 & 8, 2010

  • structural aspects

  • cristobalite

    A fibre glass

    float glass

    glassy basalt rock

    ) (... 154.0

    ,)2sin(2 2

    1

    KCunmX

    Xd

    =

    =

    ( )18022

    minmax21 =B

    Bbroadeningpeak

    2min

    2 in

    2max

    silica glass

  • nmbB

    Xb 2)422 ; (

    )2cos(21

    ==

    ) ( 154.0 ; )2sin(2 2

    1

    KCunmX

    Xd ==

    ( ) 0698.0)422; (18022 minmax2

    1 == BB

    Braggs formula relates lattice spacing d and diffraction angle :

    broadening B of diffraction peaks:

    interpretation: peak broadening B range b of translational symmetry

    interpretation: peak broadening B fluctuation = d/d of lattice spacing

    ( ) %9)422; (2tan4 21=

    ==

    B

    dd

  • SiO

    silica glass

    crystalline silica

    random packingof length-correlatedclusters1.

    2.

    W. Zachariasen (1934)

  • = 0.00

  • = 0.09

  • = 0.09; d 2 is accepted as bond

  • = 0.09; d 2 is accepted as bond

  • bond percolation diffusion path percolation

  • simulated 3D structure ofNa2Si2O5

    Vessal et al. 1992

    Greaves channels of Na+transport in Na2O-SiO2 glasses

    Greaves & Ngai 1995

  • fractured silica surface, investigated by UHV-AFMFrischat, Poggemann, Heide 2003

  • evaluate all distance correlations in the window 0.2 - 0.3 nm (O-Si-O distances)

  • evaluate all distance correlations in the window 0.2 - 0.3 nm (O-Si-O distances)

  • evaluate all distance correlations in the window 0.2 - 0.3 nm (O-Si-O distances)

  • viscosity

  • frozen-in stateloss of degree of freedom"change of lane"

    independentmotion

    beginning ofcooperative effects

    strictly correlated cooperative motion;loss of degree of freedom "velocity"

    "glass transition" on the highway

    traffic direction

    illustration of the concept of configurational entropy

    )(1

    logTST c

    Adam & Gibbs 1965

  • no translational symmetry

    no flow, fixed mean position of all elements, solid state-like degrees of freedom

    state traffic jam: state parking lot:

    translational symmetry

  • Tammanns explanation of sudden transitions due to a continuously tightened constraint

    cP = cP(conf) + cP(rot) + cP(vib) cP(rot) + cP(vib) cP(vib)

    d

    a0

    0a3d > 00 a?a3d >> 0a?d