Electrical characterization of new and aged semiconducting glazes

This paper presents the electrical characterization of antimony-doped semiconducting glazes before and after exposure to AC and DC electric fields under outdoor conditions and in the laboratory using the rotating-wheel-dip test (RWDT). Measurements of the I-V characteristics as well as dielectric spectroscopy in frequency domain (FDS) were performed on new and aged samples and results were compared. While I-V data only show a decrease in the current with aging, FDS data show more detailed features. Besides a decrease in DC conductance, a strong increase in low frequency dispersion (LFD) was found and a decrease in the relaxation polarization was indicated. The latter was more pronounced for samples aged under DC voltage. The observed relaxation polarization could originate from the presence of a low-conductive glassy surface layer on top of the "bulk" semiconducting glaze and it was weakened by the appearance of surface changes, including damage of the glassy surface layer, which thereby opened an alternative path for the current flow from the electrode to the "bulk" semiconducting glaze. The increase in LFD could be attributed to moisture trapped in the surface cracks formed during aging