Irradiation-induced nanostructures

This paper summarizes the results of our studies on the irradiation-induced formation of nanostructures, where the injected interstitials from the sou rce of irradiation are not major components of the nanophase. This phenomen a has been observed by in situ transmission electron microscopy (TEM) in a number of intermetallic compounds and ceramics during high-energy electron or ion irradiations when the ions completely penetrate through the specimen . Beginning with single crystals, electron or ion irradiation in a certain temperature range may result in nanostructures composed of amorphous domain s and nanocrystals with either the original composition and crystal structu re or new nanophases formed by decomposition of the target material. The ph enomenon has also been observed in natural materials that have suffered irr adiation from the decay of constituent radioactive elements and in nuclear reactor fuels that have been irradiated by fission neutrons and other fissi on products. The mechanisms involved in the process of this nanophase forma tion are discussed in terms of the evolution of displacement cascades, radi ation-induced defect accumulation, radiation-induced segregation and phase decomposition, as well as the competition between irradiation-induced amorp hization and recrystallization. (C) 2000 Elsevier Science S.A. All rights r eserved.