A LI-7 NMR-STUDY OF THE SUPERCONDUCTING SPINEL LI1+XTI2-XO4

The superconducting oxide spinel system Li1+xTi2-xO4 (0 less-than-or-equal-to x less-than-or-equal-to 1/3) has been studied in the temperature range 160-340 K by nuclear magnetic resonance (NMR) of the Li-7 nucleus. Elucidation of the two different Li sites (tetrahedral and octahedral) for x > 0 has been achieved via dilution of the Li-7 nuclei with Li-6. NMR linewidths show a narrowing with increasing temperature for low x, indicating that the Li ions are becoming mobile around room temperature. Observed chemical shifts show an increase at the metal-insulator transition, demonstrating that the Li nuclei act as weakly coupled probes of the bulk paramagnetic susceptibility. Analysis of these shifts, together with nuclear spin-lattice relaxation times, has allowed the Knight shift due to the Li(2s) contact to be calculated. This reveals that there is approximately 7% Li 2s character in the unpaired-electron wave function at the Fermi surface in LiTi2O4.