Thermal conductivity degradation induced by heavy ion irradiation at room temperature in ceramic materials

The thermal conductivity degradation induced by irradiation with energetic heavy ions at room temperature is studied and quantified. Three semi-metallic systems: titanium and zirconium carbides, titanium nitride, as well as a covalent compound: 6H silicon carbide were irradiated by 25.8 MeV krypton ions at 10¹⁶ and 6 . 10¹⁶ ions.cm^-2 doses to produce defects. During ion irradiation, inelastic collisions and elastic collisions occur at a different depth in a material. Two collision domains can be defined. Modulated thermoreflectance microscopy measurements were performed at differing frequencies to characterize the thermal conductivity degradation in these two domains for each of the investigated materials. Our results reveal a significant thermal conductivity degradation in the two collision domains for all materials. Elastic collisions are shown to degrade more strongly the thermal properties than inelastic ones. Scattering of thermal energy carriers is larger in elastic collision domain because displacement cascades produce a very high concentration of point defects: vacancies, interstitials and implanted Kr ions. The degradation coming from electronic interactions that seems to be more important in SiC can be explained by the presence of large populations of generated extended defects, facing to generated individual point defects in TiC, TiN or ZrC.