Update on possible electrode mechanisms in the sweeping of alpha quartz

The use of thick nonporous Au/Cr electrodes which can lead to a change in the sweeping mechanism is discussed. With these electrodes, a color-center front advances from anode to cathode in quartz that is swept in air at temperatures below the alpha - beta transition. Evidence is presented which indicates that: (1) color centers form beneath nonporous portions of the anode that correlate with the formation of interface Cr-oxides and silicides; (2) clear striae are created along the C-axis where color centers either do not form or are subsequently bleached along cylindrical volumes which correlate with openings in the anode; (3) the clear cylindrical volumes have diameters much larger than the metal openings; (4) a uniformly colored region can form in areas close to but not covered by the anode. Also, a clear band forms between the uniformly colored region and the striated region associated with the anode.<>