Thermal equilibrium vacancies in platinum studied by positron annihilation

Abstract

A detailed study of thermal vacancies in Pt by positron lifetime spectroscopy yields the vacancy formation enthalpy H 1VF = (1.35 ± 0.09) eV and the positron lifetime τ1V = 168 ps in monovacancies. The tentative fit of a model that includes mono‐ and divacancies yields an estimate of the divacancy binding energy H 2VB = (0.5 ± 0.4) eV and a positron lifetime in divacancies τ2V = 174 ps which only slightly exceeds τ1V. The present value of the vacancy formation enthalpy H 1VF is discussed in conjunction with the results of quenching experiments. A comparison with self‐diffusion data yields the vacancy migration enthalpy H 1VM = 1.34 eV which is in agreement with attributing the annealing stage at 600 to 650 K, observed after electron irradiation, to long‐range migration of monovacancies.

Breakdown of Arrhenius law of temperature-dependent vacancy concentration in fcc lanthanum

“…Since µτ b is actually not known within about one order of magnitude we use the upper limit approximation µτ b ≈ 4.4 × 10 4 in the following. This value is composed of the trapping coefficient µ = 4×10 14 s −1 (see, e.g., values for Al [22,23] and for Cu, Au, Pt [24]), and an assumed positron bulk lifetime in La of τ b ≈ 110 ps, which is in the range of 100 ps < τ b < 120 ps typically obtained for transition metals (see, e.g., calculated values for the fcc metals Cu, Ag, Ni, and Au [25]).…”