NMR Study on Defect Structure in β-LiGa

Abstract

The mechanism of superionic conductivity in β-LiGa has been investigated by ⁷Li and ⁷¹Ga NMR spin–lattice relaxation rates 1⁄T₁ in Li excess 50.0 at. %, Li deficient 44.0 and 47.0 at. % samples. The activation energies of Li⁺ ionic diffusions through free Li vacancy V_Li and through bound Li vacancy trapped by antisite Li_Ga have been estimated to be 0.13 and 0.064 eV by applying Bloembergen–Purcell–Pound (BPP) type equation to 1⁄T₁ in 50.0 at. % Li sample. In Li deficient samples, the same activation energy, 0.11–0.13 eV, for Li⁺ ionic diffusion through free V_Li has been obtained at high temperatures, and evidence for the ordering of V_Li has been also detected by anomalies at 200–240 K in the temperature dependence of 1⁄T₁ for ⁷Li. However, the motional narrowing observed in ⁷Li NMR line width above 110–130 K indicates that disorder in V_Li can still remain even below its ordering temperature in 44.0 and 47.0 at. % Li samples.