Neutron Scattering

is the Kohlrausch-William-Watts relaxation time and ß < 1 the stretching exponent .
in good approximation follows a Vogel-Fulcher temperature dependence .
(T) ~~ exp
A
T -To
(15 .2)
The temperature offset in the denominator of the exponent leads to a divergence of i
To, a temperature below Tg which, however, may never be reached in equilibrium.
15
Boson peak
10
rast
5
~s~av
0,
0
0
a
3 4 5 6 7
1000K/T
Figure 15 .1 : Relaxation landscape of PB . u and ßsio, correspond to the classical relaxation
processes and are treated here .
The dielectric ß-relaxation is considered to be a result of a partial reorientation of the
molecular dipoles in the substance .
It is interpreted as a local activated process, where the
dipole hops between two positions separated by an activation energy E .
The relaxation time
follows an Arrhenius behaviour
15-3