I. Fragility and its Relation to Other Glass Properties II. · PDF fileFragility and its...
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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
