The defects in this material were investigated by using the positron annihilation technique. The Doppler broadening profiles of the annihilation radiation and lifetime spectra of positrons were measured at temperatures ranging from 305 to 516K. The lifetime of positrons which were annihilated from the delocalized state was deduced to be equal to 0.306ns at about room temperature. At temperatures below the melting point, the observed temperature dependence of the line-shape parameter was explained by assuming that the formation energy of thermal equilibrium defects was 1eV. At temperatures above the melting point, pick-off annihilation of ortho-positronium in open spaces was observed. The size of these spaces was estimated to be 0.2nm3.

A.Uedono, M.Tachibana, M.Shimizu, M.Satoh, K.Kojima, S.Ishibashi, T.Kawano, S.Tanigawa: Japanese Journal of Applied Physics, 1996, 35[1-6A], 3623-9