Diffusion parameters of B in Cu determined by β-radiation-detected NMR

Using β-radiation-detected nuclear magnetic resonance (β-NMR) in the special form of cross-relaxation spectroscopy we studied the diffusional behavior of implanted ¹²B nuclei in Cu single crystals at temperatures T=115-750 K. An extended and completely revised dynamic theory of nuclear cross relaxation is developed to analyze the experimental data. Especially the incorporation of (hitherto neglected) spin-lattice relaxation effects turned out to be an important improvement. Applying this formalism we obtain activation energies of E_a=0.57(5) eV for the migration of interstitial B, the dominating fraction for T<~400 K, and of E_a=1.15(10) eV for substitutional B formed at higher temperatures. The previously found direct-exchange mechanism for the diffusion of substitutional B in Cu is confirmed by our analysis.