Abstract :
Experimental ionic conductivity r and
activation energy EA data in the binary sodium silicate
system are reviewed. Analysis and brief discussion
based on 48 glasses in a wide compositional range
(between 4 and 45 Na2O mol%) are presented.
Emphasis is placed on the application of the Anderson–
Stuart model to describe the variation of activation
energy EA with sodium concentration. In this
analysis were considered experimental parameters
such as shear modulus G and relative dielectric permittivity
e, also in wide compositional range. A ‘universal’
finding is obtained using log10r vs. EA/kBT in 47
of the 48 glasses investigated, where EA is the activation
energy for conduction, kB is the Boltzmann constant
and T is the absolute temperature. Using
conductivity and molar volume from density data, both
measured at 20 C in the same glasses, it was found a
remarkable common cubic scaling relation between
conductivity enhancement of the free volume due to
increase in alkali content. The drastic drop in conductivity
by 16 orders of magnitude for so many ionconducting
binary sodium silicate glasses is then caused
by structure and ion content. The effects of shear
modulus, relative dielectric permittivity and free volume
are taken into account, as also the problem of
phase separation. In particular, it is suggested that the
glass network expansion, which is related to the
available free volume, is a parameter that could partially
explain the increase in ionic conductivity for this
binary system.
