7Li Spin–Lattice Relaxation at Low Temperatures in a Superionic Conductor β-LiGa

Abstract

In order to investigate the Li + ionic diffusion and the electronic states in a mixed conductor β-LiGa with high Li + ionic diffusibility and electron/hole conductivity, 7 Li NMR linewidth and spin–lattice relaxation measurements have been performed in 44.0, 47.0, and 50.0 at. % Li β-LiGa samples at 10.03 MHz in the temperature range between 10 and 320 K. The onset temperature T MN =70 K of the motional narrowing in 50.0 at. % sample has been determined from the temperature dependence of the linewidth. The Li + ionic diffusion is found to contribute to the spin–lattice relaxation rate 1/ T 1 down to ∼0.5 T MN even below T MN where the motional narrowing does not occur. The high diffusibility of Li + ions has been proved from a microscopic point of view. At low temperatures, the relations 1/ T 1 T =3.5×10 -4 , 3.8×10 -4 , and 5.1×10 -4 s -1 K -1 are observed in 44.0, 47.0, and 50.0 at. % Li samples, respectively. The density of states of conduction electrons at the Fermi level in these compounds becomes higher with increasing Li content, which is consistent with the predictions by band calculations.