Self-Diffusion and Nuclear Quadrupolar Relaxation in fcc Lanthanum Metal

The nuclear magnetic-resonance spin-lattice ($T_1$) and spin-spin ($T_2$) relaxation times and the Knight shift of ${\mathrm{La}}^{139}$ in pure fcc lanthanum metal have been studied from 295 to 825°K. The relaxation times exhibit a temperature dependence which can be explained by vacancy diffusion and annealing effects that perturb the spin system via the nuclear electric-quadrupole interaction. At the highest temperatures, it is found that $T_1=T_2\propto \exp \left(\frac{E_a}{\mathrm{kT}}\right)$ where $E_a=15\mathrm{}$ kcal/mole is found for the activation energy of vacancy formation and diffusion. The Knight shift is found to increase from 0.64% at 295°K to 0.72% at 825°K, which may be the result of an electron-phonon interaction.