Effect of thermal history on conductivity and electrical relaxation in alkali silicate glasses |
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Authors: | Lawrence P Boesch Cornelius T Moynihan |
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Institution: | Vitreous State Laboratory, Department of Chemical Engineering and Material, Science, Washington, D.C. 20064, USA |
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Abstract: | Electrical conductivity σ0 and electric field relaxation measurements have been carried out as a function of thermal history for two alkali silicate glasses, Na2O3SiO2 and K2O3SiO2. Specimens of each glass with three different thermal histories, two of the anneal-and-quench type and one of the rate-cool type, were studied. The average structural or fictive temperature Tf of each of the specimens was characterized by measuring their indices of refraction. Effects of thermal history on σ0 and its activation enthalpy were in accord with results of previous investigators. That is, for a given type of thermal history σ0 was lower and higher the lower Tf. In addition it was found that for two specimens with the same Tf or index of refraction but different thermal histories the rate-cooled specimen exhibited a lower conductivity than the annealed-and-quenched specimen, in accord with the results of Ritland. The distribution of relaxation times τσ for decay of the electric field due to ionic migration was found to be due primarily to a distribution in the pre-exponential term ln in the equation ; the distribution in was extremely narrow. Differences in thermal history caused small differences in the distribution of τσ, but no difference in the average activation enthalpy for τσ. From this result it appeared that the dependence of the conductivity activation enthalpy on thermal history was due to the effect of thermal history on the temperature dependence of the distribution in τσ. |
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