The behavior of B impurities implanted into Cu single crystals has been investigated by means of $\beta$ radiation detected nuclear magnetic resonance and cross-relaxation spectroscopy. Diffusion of substitutional B ( ${\mathrm{B}}_s$) in Cu is observed in the temperature range of $T=600\mathrm{}–750\mathrm{K}$. By combining information from new and formerly published data it is shown that this diffusion is not mediated by any other defect; it rather takes place by a direct site exchange between ${\mathrm{B}}_s$ and neighboring Cu atoms. To our knowledge ${\mathrm{B}}_s$ in Cu is the first system for which this long discussed diffusion mechanism has been established experimentally.

• Received 5 August 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.4784