Effect of machining on dielectrical and mechanical properties of ceramics

Machining effects have been studied on model materials (pure single crystals of Al/sub 2/O/sub 3/) by different surface preparations: soft polishing (friction) and hard polishing (grinding and diamond polishing). Characterization of point defects created by machining is investigated by cathodoluminescence. Dielectrical ability to form a space charge and the stability of trapped charges is studied by the mirror method recently developed. Mechanical properties are characterized by toughness and friction test. The influence of heat treatments to restore the crystal lattice or to stabilize point defects is also studied in the same experimental methodology. Polishing is associated to the formation of oxygen vacancies which can trap electrons under electronic irradiation. Thermal treatments decrease the charge trapping ability and modify the surrounding of oxygen vacancies. The effect of friction is also discussed in comparison with the polishing results.