Characterization of thermal conductivity degradation induced by heavy ion irradiation in ceramic materials

Thermal conductivity degradation of three semi-metallic ceramics: titanium carbide, zirconium carbide and titanium nitride, and a covalent compound: 6H silicon carbide, induced by irradiation with energetic heavy ions at room temperature, is studied and quantified. Irradiations by 25.8 MeV krypton ions at 1016 and 6 x 1016 ions cm-2 doses were used to produce defects in the considered materials. Modulated thermoreflectance microscopy measurements were performed to characterize the resulting subsurfasic degradation of the thermal conductivity for each of the investigated materials. The study considers the two collision domains produced by the inelastic collisions and the elastic collisions that occur during an ion irradiation. A significant thermal conductivity degradation in the two collision domains for all materials is obtained. Elastic collisions are shown to degrade the thermal properties more strongly than the inelastic ones. The scattering of thermal energy carriers is larger in the elastic collision domain because displacement cascades produce a very high concentration of point defects. The degradation coming from electronic interactions is found to be more important in SiC, which can be explained by the presence of large populations of generated extended defects, facing generated individual point defects in the studied semi-metallic materials