Positron Annihilation in Stable and Supercooled Metallic Melts

Abstract

Abstract The stable and supercooled melts as well as the crystalline phases of Ga, In, Sn, Pb, and Bi have been investigated in the age –momentum correlation (AMOC) positron annihilation facility at the Stuttgart pelletron. The comparison of the lineshape parameter S, characterizing the momentum distribution of the annihilating electron –positron pairs, and of the mean positron lifetime with measurements of the positron diffusivity confirms in considerable detail the ‘polaron’ model of positrons in metallic melts developed earlier. The quantitative analysis of the data provides us with valuable information on the structure of the melts. E. g., in the investigated melts the existence of an appreciable concentration of ‘free volumes’ comparable in size with the atomic volume can be excluded. It is shown that this is in accord with earlier deductions from self-diffusivity measurements. An interesting but hitherto incompletely understood correlation between the entropy of fusion and the absence of trapping of positrons by vacancies in thermal equilibrium is pointed out.