FAST IONIC CONDUCTION IN GLASS: COMPOSITIONALLY INDUCED EFFECTS ON TRANSPORT PROPERTIES IN HIGH-ALKALI OXIDE GLASSES. (VOLUMES I AND II)
Abstract
The thermal and ion transport properties of glasses belonging to the families M(,2)O + nB(,2)O(,3):Al(,2)O(,3) , where n = 0, 4.0, 6.7 and M(,2)O + P(,2)O(,5), where M(,2)O is either Na(,2)O or Li(,2)O, have been investigated out to the highest yet reported fraction of M(,2)O for conventionally prepared glasses. The glass transition temperatures for the borate and aluminoborate glasses has been modeled in terms of the structural chemistry of the glass. For the B(,2)O(,3) glasses, a minimum in the conductivity activation energy, E(,act), is seen at 50mol% Na(,2)O. A similar minimum is not seen for the Li(,2)O glasses. The competing factors of ionic jump distance, tending to decrease E(,act) and the glass basicity, increasing as the alkali fraction increases and tending to increase E(,act) are analyzed in terms of a new micro-structural model of the ion conduction energetics and topologies. It is observed that the activation energy minimum arises from a rapidly increasing glass basicity in the vicinity of 50 mol% Na(,2)O. The study of the thermal properties of the binary phosphate glasses has produced the first recorded measurement of the glass transition temperature of P(,2)O(,5) glass, as well as recording the dependence of the glass transition temperature and heat capacities on alkali fraction over the full glass forming region. The phosphate glasses, though they are glasses forming out to the same high alkali fraction, show no minimum in the activation energy. The trend at high alkali is for the activation energy to decrease less rapidly at the higher alkali fractions. The phosphate glasses are observed to be poorer conductors than the other well studied silicate and borate glasses. This behavior has been analyzed according to the author's micro-structural model for ionic conduction in glass, and the lower conductivity, and hence higher activation energy observed for the phosphate glasses, is found to be largely the result of a lower density of alkali sites (at constant alkali oxide fraction) in the glass structure when compared to the silicate and borate glasses. This lower cation density is seen to lead to larger cation jump distances and to higher activation energies.
Degree
Ph.D.
Subject Area
Chemistry
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