Structural vacancies in Al–Pd–Mn quasicrystal and its (1/1, 2/1)-AlPdMnSi approximant crystals: Positron lifetime studies

Abstract

Positron annihilation lifetimes of the stable icosahedral (i) Al–Pd–Mn quasicrystal and its (1/1, 2/1)-AlPdMnSi and 1/0-Al₁₂Re approximant crystals were measured at ambient temperature. The observed single-lifetime of the i-Al–Pd–Mn quasicrystal is very close to that of the (1/1, 2/1)-AlPdMnSi approximant crystals, indicating that the same type of structural vacancies exists in all these specimens. On the other hand, the lifetime of 1/0-Al₁₂Re approximant crystal, which has no structural vacancies, is significantly shorter than the above results. We discuss the relationship between the positron lifetimes and mean valence-electron density.

Keywords:

• approximants
• positron annihilation
• quasicrystals

Acknowledgements

This work was supported by Research Fellowships of the Japan Society for the Promotion of Science (JSPS) for Young Scientists, and partly supported by a Grant-in-Aid for Scientific Research from JSPS and Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).