X-ray diffractometry and high-resolution electron microscopy of neutron-irradiated SiC to a fluence of 1.9 x 1027 n/m

Neutron-induced damage in SiC up to a fluence of 1.9 x 1027 n/m2 (E>0.1 MeV) was examined by means of X-ray diffractometry and high-resolution electron microscopy. Specimens of β-SiC were irradiated in fast breeder reactors at 370 to 650 C. The lattice parameters of all specimens were increased by the irradiation, but above 2 x 1026 n/m2 lattice expansion decreased and was accompanied by significant peak broadening. Electron microscopy revealed a high density of interstitial loops on {111}, where X-ray diffraction peaks showed marked broadening. Peak broadening could be attributed mainly to the crystallite size effect at lower fluences, but a strain contribution was significant above 2 x 1026 n/m2. Electron diffraction patterns and high-resolution images indicated preservation of crystallinity up to the highest fluence observed. Thermal annealing up to 1000 C did not affect the peak broadening and average loop diameter. Above 1400 C, decrease in lattice strain and increase in crystallite size with increasing annealing temperature were observed. (orig.)