EPR-active Dimer Centers with S=1 in Α-Al2o3 Single Crystals Irradiated by Fast Neutrons

Corundum (alpha-Al2O3) possesses a number of unique properties, including high tolerance to harsh radiation environment. Material functionality is strongly affected by radiation-induced structural defects, single interstitial-vacancy Frenkel pairs and their aggregates. Three novel paramagnetic two-electron defects with total spin S = 1 have been revealed in fast neutron irradiated alpha-Al2O3 single crystals by means of the EPR method. Analysis of the EPR characteristics of these defects allows to conclude that the main novel D 1 defect (initial concentration after irradiation about 2.8 x 10 16 cm -3) is oriented along one of three equivalent b crystal axes, that connect two adjacent anion sites of oxygen triangles on the base corundum plane. The D 1 defect is ascribed to the F-2( 2+) center (two adjacent single-charged oxygen vacancies), while the D 2 and D 3 have the same dimer structure with an additional defect in their vicinity. The suggested defect structure is supported by pulse annealing of the EPR signal of relevant defects: defect concentration dependence contains a rising stage at 500-630 K, while complete thermal destruction due to the recombination with complementary oxygen interstitials occurs by 720-750 K. Such behavior qualitatively coincides with earlier studied thermal annealing of the F-2( 2+) center optical absorption in neutron-irradiated corundum.(c) 2022 Elsevier B.V. All rights reserved.