Thermally- and irradiation-induced sulphur aggregation in Ni–S ageing system studied by positron annihilation

Effect of phosphorus on vacancy-type defect behaviour in electron-irradiated Ni studied by positron annihilation

“…The value of the S-parameter for pure Ni is increase at temperatures 350-400 K that is due to the formation of the three-dimensional vacancy clusters (3D-VCs) [14] (see Fig. 1a).…”

“…The doping with P also enhances markedly the vacancy aggregation in bcc Fe [13]. We have shown recently [14] that sulphur atoms in Ni strong interact with vacancies (V) and V-S pairs form the nanovoids decorated with sulphur atoms. We have also observed vacancy clusters decorated with phosphorus atoms in austenitic Fe-36%Ni alloys with addition of P [11].…”

“…Since positively charged nuclei are absent at vacancy-type defects, positrons are trapped and annihilate there with the surrounding electrons, conveying the information on the local electronic environment around the vacancy-type defects. Coincidence Doppler broadening [13] and angular correlation of annihilation radiation (ACAR) [14] enables us to identify the chemical element whose electron annihilate with the positron, by measuring the electron momentum distribution in the high-momentum region, given by the positron annihilation with the core electrons. It can identify the chemical environment of the annihilation site, because the core electrons are tightly bound to the nuclei and almost unaffected by crystal structure.…”

“…It can identify the chemical environment of the annihilation site, because the core electrons are tightly bound to the nuclei and almost unaffected by crystal structure. Thus, those methods can probe the formation both vacancy-type defects, with sensitivity starting from the atomic size to large vacancy clusters and nanovoids [12], and the vacancy-solute complexes [13,14], whereas they are insensitive to interstitial atoms and their small agglomerates. However, the accumulation and annealing kinetics of the vacancy-type defects may be affected not only by the interaction of vacancies with solute atoms, but also by rearrangements of the SIA-solute atom complexes formed during irradiation.…”