Li Ion diffusion in nanocrystalline and nanoglassy LiAISi2O 6 and LiBO2 - Structure dynamics relations in two glass forming compounds

In the present study the Li diffusivity in nanostructured samples of two glass forming model systems, spodumene (LiAlSi2O6) and lithium metaborate (LiBO2), was examined using 7Li nuclear magnetic resonance (NMR) spin-lattice relaxometry and dc conductivity measurements. The nanostructured samples were prepared by high-energy ball milling of the respective crystalline starting material on the one hand and the corresponding glass on the other hand. The diffusivity of the glass exceeds that of the crystalline sample for both systems. However, when the crystalline samples are mechanically treated by ball milling the diffusivity is enhanced. Nevertheless, the diffusivity of these nanocrystalline samples remains lower than that of the corresponding glass. Surprisingly, when the glassy samples are treated in the same way the diffusivity decreases. After sufficiently long milling times the diffusivity of these nanoglassy samples approaches that of the nanocrystalline samples. This convergence effect seems to be due to structural relaxation processes as is suggested by supplementary infrared spectroscopy and 27Al, 12B magic angle spinning NMR measurements. © by Oldenbourg Wissenschaftsverla