Atomic vacancies in quasicrystals: Positron annihilation spectroscopy and time-differential dilatometry

For specific studies of atomic vacancies in quasicrystals the sensitive techniques of positron annihilation spectroscopy and time-differential dilatometry are employed. In the quasicrystals and approximants studied here, structural vacancies can be observed at ambient temperatures with atomic concentrations higher than 10^-4. With in situ measurements of the positron lifetime and of time-differential dilatometry after fast temperature changes at high temperatures on i-Al70.2Pd21.3Mn8.5 the formation and migration of thermal vacancies can be observed. We additionally demonstrate that the chemical environment of structural vacancies in i-Al70.2Pd21.3Mn8.5 at ambient temperatures is dominated by Al atoms. This is shown by the characteristic core electron momentum distribution as monitored by coincident Doppler broadening studies of the positron-electron annihilation photon line.