Model for radiation-induced electrical degradation of α-Al2O3cr

Abstract

When a ceramic oxide with an applied electric field is subjected to extended irradiation with energetic particles at elevated temperatures, the electrical conductivity has been reported to increase, a phenomenon termed radiation-induced electrical degradation ͑RIED͒. In the present study ␣-Al 2 O 3 crystals were subjected to 1800 V/cm while irradiated with 1.8 MeV electrons at 773 K. Above a critical dose the conductivity increased. During the conductivity enhancement, the applied field was reversed, resulting in a decrease in the conductivity. This result demonstrates that RIED was caused by carriers injected from the electrodes, in concert with electrons and holes created during ionizing irradiation. A model for RIED is proposed: the injected carriers are trapped mainly at impurities near the electrodes, leading to formation of dislocations. These dislocations serve as traps for electrons and holes generated during ionizing radiation. A network of interconnecting dislocations is associated with the enhanced conductivity.

Relationships between microstructure, mechanical and dielectric properties of different alumina materials

“…It is not useless to note that toughness, measured here by indentation, comprises problems of indenter-alumina friction associated with creation of dislocations 22 and then cracking just like the observations made in dielectric breakdown. 23 …”

“…12 Wear of ceramics, analysed using the classical mechanical properties (in particular hardness and toughness) is reported through several experimental studies [16][17][18][19][20][21] connected with such parameters as the grain size or the porosity. On the other hand, phenomena, such as dielectric breakdown, transition mode from mild wear to severe wear, 18 increase in the number of dislocations in brittle ceramics during indentation test 22 or before breakdown, 23 remained misunderstood until taking into account of the polarization property of non-conductive materials. 12,13,17,[23][24][25] Indeed, all the materials, in particular the insulators, during contacts are subject to the developing of electrical charges and the appearance of electric fields.…”

“…On the other hand, phenomena, such as dielectric breakdown, transition mode from mild wear to severe wear, 18 increase in the number of dislocations in brittle ceramics during indentation test 22 or before breakdown, 23 remained misunderstood until taking into account of the polarization property of non-conductive materials. 12,13,17,[23][24][25] Indeed, all the materials, in particular the insulators, during contacts are subject to the developing of electrical charges and the appearance of electric fields. [26][27][28] In fact, during friction, excess electric charges are injected into an insulator.…”

Electronic and defect processes in oxides. The polaron in action

“…In the electric stressing of MgO [50] dislocation densities as high as 1O1O cm/cc may result prior to breakdown. The detailed mechanism proposed involves several stages.…”

Electric charge trapping, residual stresses and properties of ceramics after metal/ceramics bonding

“…This energy can be sufficient to create dislocations which appear in the alumina lattice, thus creating new sites of trapping. 25 These created dislocations are mobile and subjected to an electric field. Consequently, an increase in the trapping of the charges occurs but these charges do not remain localized (mirror not very stable and Q p /Q m < 1).…”