Effect of melt temperature on the dc conductivity of GeO2 glasses

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Abstract
The dc electrical properties of a series of high purity GeO2 glasses fused and equilibrated at various temperatures (Tφ) in air were measured. Tφ ranged from 1200 to 1690 °C. The observed changes are not correlated changes in concentration of any of the impurities as determined by neutron activation analyses or IR measurements of OH concentrations. The resistivity was found to obey an Arrhenius function with enthalpy of activation of approximately 1.0 eV for all Tφ’s except for Tφ =1200 °C. The charge carrier was concluded to be the Na+ ion. The mobility of the Na+ ion was calculated and was found to be a function of Tφ. We suggest that the change in Tφ results in a change in the configuration coordinates of the average interstitial sites through which the Na+ ion moves. This change results in differences in the vibrational energy structure of the interstitial sites. These differences are manifested in the entropy of activation. With changes in the entropy of activation, the preexponential term changes, producing the variation in mobilities which is observed.

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