Evidence from positron annihilation of anomalously low vacancy density in some metals with low melting points

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Abstract
Measurements of the Doppler broadening of the annihilation energy spectrum in In, Sn, and Tl indicate anomalously low vacancy density below the melting temperature, Tm. In these metals the ratio of the threshold temperature for trapping by vacancies, vTt, to the temperature of melting, Tm, takes values of 0.76,0.88, and 0.70, in contrast to the value of 0.63 found in most close-packed metals. The vacancy formation enthalpies, H1vf, deduced from the threshold temperatures are 0.42, 0.57, and 0.52 eV for In, Sn, and Tl. There is no consistent pattern in the prevacancy behaviour of these metals. The positrons seem to sense the potential white–gray transition in β-Sn, even though no detectable fraction of the material experiences a phase change.

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