ION-BEAM-INDUCED AMORPHIZATION OF COMPLEX CERAMIC MATERIALS MINERALS

Radiation-induced amorphization of complex ceramics is of interest for a wide range of fields in materials science and engineering, which go well beyond the study of metamictization. Applications include the development of materials for advanced nuclear reactors, the evaluation of the long-term durability of nuclear waste forms and surface modification for physical property improvement. Amorphization is a fundamental solid-state process, and ion beam irradiations provide an effective way to study the process under well-controlled conditions. In-situ TEM with ion irradiation and HRTEM have been used to study the radiation-induced amorphization of a group of complex ceramic materials. At room temperature, there is a correlation between the critical amorphization dose and: (1) structural complexity (e.g., number of distinct cation sites), (2) chemical complexity (e.g., number of different atom types), (3) average bonding ionicity (percentage of ionic bonding versus covalent bonding), and (4) melting points (a qualitative measure of bond strength). The critical amorphization dose increased with decreasing structural and chemical complexity, increasing average bond ionicity, and increasing melting temperature of the target materials. In the ion energy range studied (<1.5 MeV), nuclear interactions between energetic particles (ions and recoils) and target atoms (elastic collision), rather than ionization effects, are primarily responsible for ion-beam-induced amorphization. HRTEM of samples irradiated at low ion doses indicated that amorphization occurred directly in the displacement cascades. © 1992, Materials Research Society. All rights reserved.