Recovery behavior of neutron-irradiated aluminum nitride with and without containing interstitial dislocation loops

Abstract

Recovery behavior of the same AlN but neutron-irradiated with different conditions was studied by using XRD and dilatometry. Length recovery rates at each isothermal annealing step were analyzed by first to second-order kinetics. The specimen irradiated at lower neutron fluence at low irradiation temperature responded isotopic unit-cell expansion, which indicated random dispersion of point defects of vacancies and/or very small defect clusters. From irradiation temperature up to 523 K, the results of Arrhenius’ plot applied for second-order kinetics gives an activation energy value of 2.9 eV. An intermediate region, 573 to 1023 K, was represented by a slightly lower activation energy of 2.0 eV. For the first lower temperature range, migration of VN may be the mechanism and that of VAl for the second stage. At high-temperature region, 1073 to 1423 K, represents final constant recovery before the saturation of length recovery. In this region, the high activation energy of 5.8 eV was observed. It is supposed that dissociation of the vacancy-antisite cluster, interstitial nitrogen cluster, or formation of a complex containing vacancy and antisite can be candidate mechanisms. The specimen containing interstitial loops after the medium fluence at higher temperatures did not recover up to 723 K, indicating almost free of independent interstitials. Between 773 and 1123 K, recovery required a similar amount of energy to the high-temperature region of the lower fluence specimen (5.8 eV), and then the same mechanism could be applied. In the second region, 1173 to 1423 K, with a very high activation energy of ~18 eV, remarkable large and quick shrinkage was observed. Large volume shrinkage may be the result of diminishing anisotropic lattice swelling, i.e., unit-cell volume expansion by internal strain is relieved.