Influence of gamma-irradiation sterilization on the structural defects of sapphire single crystals (α-Al2O3)

The influence of sterilization by gamma rays on the structure and the electrical behaviour of sapphire single crystal (alpha -Al2O3) was studied successively by thermoluminescence, by cathodoluminescence and by observation of the scanning electron microscope mirror effect. The mirror method allowed us to measure the capacity of an insulating material to trap electrons. The structural analysis of the alpha -Al2O3 showed that there were oxygen vacancies, as well as chromium and titanium impurities. It was possible to demonstrate that these defects, especially the oxygen vacancies, are in a different state after a 30 kilogray irradiation. The valency state changes of these defects and the presence of trapped charges are accompanied by a deformation of the crystalline lattice which results in a modification of its electrical properties. At room temperature, the irradiated alpha -Al2O3, unlike non irradiated alpha -Al2O3, is capable of trapping electrons. It can be concluded that gamma-ray sterilization modifies the cohesive energy of alpha -Al2O3, which could lead to mechanical changes (surface charge, friction, wear, fracture strength,...) in this material.