Atomic Resolution Imaging of Black Spot Defects in Ion Irradiated Silicon Carbide

Abstract

Silicon carbide is of great interest as a nuclear fuel cladding material. At relatively low irradiation temperatures (< 1000 C) and doses (< 10 dpa or displacements per atom), the major irradiation induced defects are black spot defects (BSD), which appear as nanometer scale black spots in bright field transmission electron microscopy (TEM) images [1,2]. BSDs are associated with radiation-induced swelling [1]. The detailed internal structure of BSD is unknown. We are working towards understanding the structures and evolution of BSD by combining high resolution scanning transmission electron microscopy (STEM) and defect structure modeling [3]. We have irradiated single-crystal 4H-SiC and polycrystalline 3C-SiC with two ion species. One is 3.15 MeV carbon ions to a dose of 5.14 × 10 16 at/cm 2 at 870 K, 1070 K, and 1250 K. The other is 1 MeV krypton ions to a dose of 3 × 10 14 at/cm 2 and 6 × 10 14 at/cm 2 at 870 K, 1070 K. The corresponding damage levels are 0.4 dpa for carbon irradiation at 1 μm implantation depth, and 0.4 dpa / 0.8 dpa for krypton irradiation at 0.3 μm depth. TEM observation was performed at 300 kV in a FEI Tecnai TF30 and STEM observation was performed at 200 kV in a probe Cs-corrected FEI Titan.

Small-Angle Twist Grain Boundaries as Sinks for Point Defects

“…In this study, we investigate defect kinetics in {001} and {111} small-angle twist GBs and elucidate how these GBs evolve to accommodate defects in cubic SiC. Cubic SiC is of interest to applications in the nuclear reactor technologies because of its good mechanical strength, high-temperature stability, and low neutron capture cross-section 26 – 31 . Here, we focus on behavior of interstitials because defect flux to GBs in irradiated SiC is expected to be dominated by interstitials rather than vacancies based on predictions from ab initio based rate theory models 17 , 32 .…”