Tailoring Thermal Conductivity Anisotropy Using Ion Beam Modification

We demonstrate utilization of energetic particle to introduce few nanometer-sized features in crystalline solids leading to changes in thermal transport. This integrated analysis includes ion irradiation, microstructure characterization using transmission electron microscopy, measurement of thermal conductivity tensor using spatial domain thermoreflectance, and modeling of thermal conductivity accounting for observed nanostructure. In cubic CeO₂ bombarded with 2 MeV energy protons faulted dislocation loops are formed. These loops have long range strain field resulting in significant reduction of thermal conductivity. Aligned ion tracks in Al₂O₃ generated by bombardment with 167 MeV xenon ions modify its thermal conductivity anisotropy, where thermal conductivity along direction perpendicular to ion channels exhibits larger conductivity reduction compared to direction parallel to the channels. Lastly, we show modification of conductivity anisotropy in hexagonal delta-phase U-Zr alloy, caused by formation of platelet nanoprecipitates. For the latter case, the anisotropic modification is also observed in phonon lifetimes measured using inelastic X-ray scattering.