Positron lifetime studies for Ce-based bulk metallic glasses

Positron lifetime and coincident Doppler broadening (CDB) spectroscopy were conducted for Ce₇₀Al₁₀Cu₂₀ bulk metallic glass (BMG) to study the local atomic structure. A single component positron lifetime of ∼246 ps corresponding to annihilation in the free volume intrinsic to the local structure of BMG glassy matrix was obtained. CDB spectroscopy revealed that the free volume is dominantly surrounded by Ce atoms. Positron lifetime for Ce₇₀Al₁₀Cu₂₀ BMG is much longer than that of Ce₆₈Al₁₀Cu₂₀Nb₂ BMG, which is caused by the diffusion of Nb atoms into the vacancy-sized free volumes in the Ce-Al-Cu matrix. In addition, the positron lifetime for Ce-Al-Cu BMG is much different from those of Ce-Ga-Cu BMGs where two positron lifetime components τ₁ ∼ 129 ps and τ₂ ∼ 261 ps attributable to the densely-packed glassy state and free volume, respectively, are found. The present results imply that Ga plays an important role in triggering off the formation of the densely-packed glassy state. (author)