High-temperature ac conductivity of amorphous SiO2: Fused silica and thin thermal films

High-temperature ionic conductivity of both fused silica and thin films the rmally grown on a silicon substrate has been investigated in the temperatur e ranges 700-1400 and 570-830 K, respectively, by means of impedance spectr oscopy. The results for both types of materials may be interpreted as being due to the existence of an extrinsic conduction mechanism related to the p resence of dissociated sodium ions. The numerical analysis of the experimen tal results led to values of 1.3 and 0.6 eV for the dissociation and migrat ion energies, respectively. The dissociation energy turns out to be in good agreement with the value obtained in crystalline quartz and related to the aluminum-alkali ([AlO4-M](0)) center; moreover, good agreement is also fou nd between the mobility value obtained here and literature data evaluated o n thin films by different electrical techniques. No influence of hydrogen c ontent on alkali transport was found by considering wet and dry samples, at variance with results previously obtained on crystalline quartz. [S0163-18 29(99)14515-6].