Isotope Effect for Self‐Diffusion in Single Crystals of Silver

Abstract

The simultaneous diffusion of ¹⁰⁵Ag and ¹¹⁰Ag in silver single crystals has been measured over the temperature range 640 to 955 °C. The strength of the isotope effect has a constant value of 0.718 ± 0.011 for T < 750 °C, but decreases with further increases in temperature to a value of 0.639 ± 0.013 at 937 °C. This temperature dependence is significant at the 90% confidence level. Although one may explain the observed decrease by the temperature dependence of ΔK, we consider it more likely that the decrease results from the simultaneous operation of vacancy and divacancy mechanisms. At the melting point, the contribution of divacancies is from 11 to 45% of the total self-diffusivity. The diffusion coefficient of ¹¹⁰Ag in Ag single crystals over the same temperature range was also obtained from these experiments. The least squares Arrhenius line is described by D₀ = 0.67 cm²/s, Q = (45.2 ± 0.2) kcal/mol ( = (1.97 ± 0.1) eV). The values of D deviate systematically from this line in the manner expected for simultaneous vacancy and divacancy diffusion, although the statistical significance of these deviations is not certain.