Recovery behavior of neutron-irradiation-induced point defects of high-purity β-SiC

To evaluate neutron-irradiation-induced crystalline defects and its thermal stability, high-purity β-SiC ceramics consisting of only 3C polytype were neutron irradiated using the BR2 reactor up to 2 × 1024 n/m2 (E > 0.1 MeV) at a low temperature of <363 K. Change in macroscopic length resulting from post-irradiation isothermal annealing up to 345 min between room temperature and 1623 K was measured using a high-precision dilatometer. Correspondence of macroscopic linear swelling and that of the lattice parameter of β-SiC specimen was excellent, and the swelling was fully recovered by the annealing, indicating the presence of only simple defects. Amorphization did not occur. Calculation of activation energies, obtained from precise length measurement during each isothermal annealing step, revealed that length recovery behavior between 423 and 1673 K could almost be explained by a first-order reaction, and it was found there were at least four stages with different activation energies. Furthermore, an obvious discontinuity around 1173-1273 K was observed. The activation energies for each temperature range of 3C-SiC and those of 6H-SiC were mostly the same and basic recovery features were similar for both polytypes. However, transition temperatures were slightly different.