Multi-nuclear NMR study of polytype and defect distribution in neutron irradiated silicon carbide

Silicon carbide containing 92% β-SiC has been irradiated in a material test reactor at a fast neutron fluence (>0.1MeV) of 3.39×1021ncm−2 at an average temperature of 796°C, and subsequently studied by 29Si and 13C MAS NMR spectroscopy. A small amount of structural alteration was measured with the α-SiC polytypes increasing from around 8–14%. Based on the assumption that the primary dominant defect is the paramagnetic SiV- defect. The defect concentration has been measured in both the irradiated and unirradiated sample using spin lattice relaxation time (T1) data obtained via a saturation-recovery experiment and was found to increase from 4.6×1018cm−3 to 1.5×1020cm−3. A case is presented to show that a small residual internuclear dipolar coupling contribution (at 3.80×10−6% of its total value) towards the T1 in the unirradiated reference sample significantly modifies the relaxation time from a value based solely on the dominant nuclear defect coupling mechanism.