Thermal conductivity degradation of silicon-ion-irradiated silicon carbide ceramics

Silicon carbide (SiC) ceramics, fabricated by spark plasma sintering (SPS), were irradiated by 14 MeV silicon ions at 300 °C across a dose range of 0.01 to 1.00 displacements per atom (dpa). Thermal diffusivity and elastic modulus of the irradiated layers were measured using Transient Grating Spectroscopy (TGS), revealing significant diffusivity reduction even at 0.01 dpa. In-situ annealing of a 0.5 dpa sample showed diffusivity recovery starting just above the irradiation temperature, with a 2.5 % restoration after annealing at 712 °C, equivalent to approximately 26 % recovery in defect concentration. X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) showed no phase transformations but indicated lattice expansion, local structural changes, and reduced elastic modulus with increasing radiation damage. The linear relationship between irradiation-induced defect thermal resistance and estimated swelling from lattice expansion, along with microscopy observations, suggest that radiation-induced defects below 1 dpa remain isolated or form small clusters <1 nm, consistent with black spot defects (BSD). Even at low concentrations, these defects significantly degrade the thermal conductivity of SiC.