The surface conductivity of gamma-irradiated ceramic dielectrics

We have studied the surface dc conductivity of commercial alumina based ceramic dielectrics of the UF-46 and GB-7 types in a temperature interval from 200 to 400 K before and after gamma irradiation to a dose of 10⁴–10⁵ Gy. The two ceramics differ in the content of the α-Al₂O₃ crystal phase (72 wt % for UF-46 versus 86 wt % for GB-7) and in the total specific area of the grain boundaries (3.40 m²/kg for UF-46 versus 4.56 m²/kg for GB-7). In the temperature interval studied, the surface conductivity obeys a power law with the exponent dependent on the grain boundary area and the gamma radiation dose. Irradiation leads to a significant decrease in the exponent, the effect being more pronounced for ceramics with a greater grain boundary area. It is suggested that the electric conductivity proceeds according to a polaron mechanism, with a multiphoton character of the corresponding electron transitions.