Ag Ion Transport and Deposition in α Quartz

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Abstract
Contact of a negatively charged microprobe to the (0001) face of a silver‐backed Madagascar αquartz crystal at temperatures between 300–573°C produced four distinct types of visible decorations. The most prominent of these were conducting metallic platelets on the basal plane about 0.4 μ thick, with surface areas ranging up to the dimensions of the anode. The growth of these platelets appeared to take place only at the periphery, and to be thermally activated with dependence upon field ε of the form exp[−(H0−βε½)/RT], where β=0.32 kcal/[mole(V/cm)½] and H0=38 kcal/mole. Metallic platelets which formed deep within the crystal bulk, having relatively large surface area usually caused the crystal to fracture. The migration of silver through the crystal bulk was observed to take place only in the [0001] direction. Geometric patterns showing the sixfold symmetry of the basal plane were observed to form, at or near the crystal surface, within a fraction of a second upon the application of a negative probe to the (0001) face. Probe currents, both axial and equatorial, were found to be thermally activated with energies between 38 and 39 kcal/mole for conduction not involving the transport of silver ions. Platelet formation in synthetic quartz crystals differed markedly from that for natural quartz. Instead of a conducting metallic platelet, an irregular dendritic growth appeared.