Relationships between conductivity and apparent glass basicity. Conductivity maximum in glass

Abstract

Studies of the compositionally dependent conductivity in pseudo-binary xNa 2 O·(1− x)[ nB 2· Al 2 O 3] glasses have been carried out to 60 mol% Na 2O. For n=4.0, at x = 0.50 Na 2O, a local maximum conductivity is observed. Due to a simultaneous exponentially increasing conductivity preexponent, A, the conductivity maximum is not persistent. In the same composition region, however, E act, the conductivity activation energy, passes through a minimum value of 55kJmol −1. The activation energy minimum in these glasses is analyzed in terms of the competition, with increasing alkali, between decreasing jump distances tending to decrease E act and the increasing post-polarization charge density residing at the non-bridging oxygens tending to increase E act. The analysis suggests that the coulombic energy, to which both these effects contribute, in the high alkali glasses, is dominated by the latter effect. These observations are analyzed in terms of the glass micro-structure and the conduction energetics-topologies recently correlated by the author.