Theoretical calculation of positron lifetimes for defects in solids

Abstract

Theoretical calculations of positron lifetimes for vacancy defects in B2-type intermetallic compounds (FeTi, CoTi and NiTi) and MgO have been performed using DV-Xα method. In B2-type intermetallic compounds, the charge transfer from Ti to Fe/Co/Ni induces the difference of the positron localization between the Ti vacancy and Fe/Co/Ni vacancy. At the Fe/Co/Ni vacancy surrounded by the positively charged Ti atoms, the positron is not well localized and yields a shorter positron lifetime than at the Ti vacancy. Our recent positron lifetime measurement for MgO reveals that the bulk positron lifetime of MgO is about 30 ps shorter than the previously reported value. The experimental positron lifetime for the bulk state is well reproduced by the semiconductor model. The comparison of calculated and experimental positron lifetimes for the Mg vacancy suggests that the inward relaxation occurs around the Mg vacancy trapping the positron.