Postradiation Defects in Neutron-Irradiated Pyrolytic Boron Nitride

Defect Engineering of Monoisotopic Hexagonal Boron Nitride Crystals via Neutron Transmutation Doping

“…The first is a defect with an electron spin S = 1/2 and a g -value of 2.003 interacting with 2 equivalent nearby nuclear spins I = 1 (100% abundance) that gives rise to a five-line spectrum with a line intensity ratio of 1:2:3:2:1, where the nuclei are most likely 14 N. Toledo and Krambrock referred to this defect as D3 from the EPR of neutron-irradiated hBN flake powder samples. Interestingly, this defect was first reported by Kabyshev et al 30 years ago where the S = 1 defect (described above) and this five-line S = 1/2 defect were both detected in their neutron-irradiated pBN samples. Toledo and Krambrock have tentatively assigned EPR signal D3 to C N V B pair defects formed by residual carbon impurities occupying nitrogen lattice sites adjacent to boron vacancies.…”

“…In particular, the two pairs of widely split lines (enhanced by a factor of 16 as shown by the green curves) appeared with the applied magnetic field oriented perpendicular to the sample surface (bottom spectrum in Figure c). These four lines were actually first reported 30 years ago by Kabyshev et al (referred to as “B-lines”) from their EPR study of neutron-irradiated pBN. The simultaneous appearance of the extremal EPR signals is related to the particular crystal structure of pBN with a strong orientation of the basal planes parallel to the surface but with some tilting of these grains off from the surface normal.…”

“…Potentially, this neutron transmutation can be produced with a homogeneous spectral distribution by controlling the types and spatial distribution of defects . Past NTD studies have focused on several BN materials with many native impurities and defects such as commercial BN powders, , hot-pressed BN, pyrolytic BN (pBN; hBN with a fine-grained, partially ordered structure), and BN nanotubes . The presence of these native impurities and defects can complicate the interpretation of the defect structures after neutron irradiation.…”