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

Abstract Silicon carbide containing 92% β-SiC has been irradiated in a material test reactor at a fast neutron fluence (>0.1 MeV) of 3.39 × 10 21 n cm −2 at an average temperature of 796 °C, and subsequently studied by 29 Si and 13 C 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 Si V - defect. The defect concentration has been measured in both the irradiated and unirradiated sample using spin lattice relaxation time ( T 1 ) data obtained via a saturation-recovery experiment and was found to increase from 4.6 × 10 18 cm −3 to 1.5 × 10 20 cm −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 T 1 in the unirradiated reference sample significantly modifies the relaxation time from a value based solely on the dominant nuclear defect coupling mechanism.