Positron annihilation in vacancies at grain boundaries in metals

Comparison of Grain Boundary Structure in Metals and Semiconductors as Probed by Positrons

“…Previous theoretical studies based on classical molecular dynamics or similar methods (see e.g. [2,3]) show that vacancies at GBs in metals are not very stable objects and delocalize i.e. lose their free volume at rather moderate temperatures of a few hundred K. This means that in real metallic materials all vacancies should be delocalized and no apparent free volumes at GBs should be observed, which is in discrepancy with experimental observations (see e.g.…”

“…This is quite high temperature and very likely the system was not in thermal equilibrium, because it should melt at such temperature, which was not the case. We could not observe vacancy delocalization up to 1500 K and therefore we had to increase the temperature to 2000 K. Interestingly, vacancy delocalization was observed in [2] at much lower temperatures (below 600 K). We also calculated the lifetime and binding energy for the conguration shown in Fig.…”

“…The meaning of the GB designation is analogous to that for the Fe GB explained above. This GB has been studied already in [2] using molecular dynamics and the details of ab initio investigations of this GB will be published elsewhere [9]. Here we note that also in this case several GB congurations exist and we choose the one with a mirror plane at the GB.…”

“…A coherent (defect free) GB in a metal possesses some free volume (called often excess free volume) which, however, increases only slightly the positron lifetime [2], and some larger free volume is therefore necessary to explain experimental PA data for nc materials. Previous theoretical studies based on classical molecular dynamics or similar methods (see e.g.…”

Simulation of Positron Annihilation Response to Mechanical Deformation of Nanostructured AgCo

“…Similar interaction between FVs occurs also at grain boundaries as shown in Refs. [15,16]. Understanding how the interaction between defects influences PL and HMP seems to be essential for proper interpretation of the experimental results.…”