On the measurement of radiation induced electrical degradation in insulating materials

Search for radiation-induced electrical degradation in ion irradiated sapphire and polycrystalline Al2O3

“…Thus the error due to surface leakage conductance, given by ⌬ / ϭR P R cG /R PG R G , 22 where R P is the volume resistance of the specimen, was always below 10 Ϫ5 . This means that for the first time in our RIED studies, 9,22,23,41 surface leakage conductances could be kept lower than the volume conductance during the whole course of the irradiations.…”

“…Thus the error due to surface leakage conductance, given by ⌬ / ϭR P R cG /R PG R G , 22 where R P is the volume resistance of the specimen, was always below 10 Ϫ5 . This means that for the first time in our RIED studies, 9,22,23,41 surface leakage conductances could be kept lower than the volume conductance during the whole course of the irradiations. The achievement of an improved accuracy of the bulk conductivity measurement under the restricting conditions of an irradiation experiment were the result of a number of special efforts: ͑1͒ using a turbomolecular pump with oil-free magnetic bearings at the specimen chamber ͑diminishing hydrocarbon contaminants͒ and irradiating only the specimen area in the region of the center electrode ͑limiting radiation-enhanced contamination effects͒, and ͑2͒ susceptibility of crack formation was reduced by a thick and soft soldering foil as compliant layer ͑low temperature dislocation mobility͒ used between the specimen having a polished surface ͑in order to avoid stress concentration at surface grooves͒ and the specimen holder consisting of Vacon70 ͑for minimization of differential thermal stresses͒.…”

“…Surface leakage currents have been unduly neglected in many previous RIED studies. In response to these difficulties, measurement and report of the surface resistances R PG and R G and ͑depending on type of contact͒ of the contact resistance R cG , which enable the calculation of the surface leakage conductance in electrically guarded experiments, 22 has been demanded for all future RIED experiments at the 1993 International Energy Agency workshop on irradiation effects in ceramics. Nevertheless, only in few experiments ͑including recent RIED studies͒ this important rule has been followed.…”

“…The back sides were soldered to metallic holders of alloy Vacon70. 22 No microcracks were detected while scanning the specimens in a scanning electron microscope equipped with field emitting electron source. 41 The specimen temperature was controlled via a thermocouple inserted into the holder 1 mm below the specimen.…”

Role of specimen thickness on the electrical conductivity of single crystalline alumina under electron irradiation

“…On the other hand, RIED became controversial when other groups failed to find RIED in alumina with 1-2 MeV electrons, with 28 MeV He ϩ ions and with fast neutrons. [12][13][14][15][16][17][18][19] Jung et al, 20 Kesternich et al, 17,21 and Kinoshita et al 13,15 found RIED-like behavior in alumina that was not a bulk effect, could be explained by surface contamination or internal fracture of the insulator. Hodgson 10 has found the production of point defects during irradiation by optical spectroscopy which influences the observed microstructural changes.…”