Ag Ion Migration in α Quartz

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Abstract
Ag ion conduction currents in α quartz were measured at temperatures between 300° and 550°C with 2.5 V dc applied between Ag electrodes on the inner and outer surfaces of a natural quartz tube. The activation energy H for this conduction process depends upon the average electric field intensity according to the equation H=H0‐βE½, where H0=38 kcal/mole and β=0.32 kcal/[mole (V/cm)½]. A theory which appears to explain this field dependence postulates the formation of a lattice‐bound negative space charge near the Ag anode. This space charge is formed by the migration of mobile impurity cations away from the anode, leaving behind a net charge due to the presence of substitutional ions such as Al+3. This negative space charge creates electrical field intensities of the order of 105 to 107 V/cm at the anode surface. This field lowers the height of the 38‐kcal/mole barrier near the anode. Graphs of the available data for Li+ and Na+ migration indicate that the rate‐limiting step for these processes might also be the surmounting of a potential barrier near the anode‐quartz interface.

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