Temperature dependence of positron diffusion in cubic metals

Abstract

We have applied a slow-positron-beam technique to extract quantitative results for the positron diffusion coefficient in high-purity defect-free Mo, Al, Cu, and Ag single-crystal samples in the temperature range 20--1400 K. The value of the diffusion coefficient ${\mathit{D}}_{+}$ at 300 K is 1--2 ${\mathrm{cm}}^{2}$/s, and it follows a power law ${\mathit{D}}_{+}$\ensuremath{\propto}${\mathit{T}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\alpha}}}$ as a function of the temperature T with \ensuremath{\alpha}=0.5--0.6 in the studied temperature range. The results show that positron diffusion is largely limited by scattering from longitudinal acoustic phonons. A good agreement with band-structure calculations is obtained with the positron effective mass ${\mathit{m}}^{\mathrm{*}}$\ensuremath{\approxeq}1.5. The terms affecting the temperature dependence of the sum of the positron and electron chemical potentials are extracted.