Li+ ionic diffusion and vacancy ordering in β-LiGa

Abstract

⁷Li and ⁷¹Ga NMR measurements have been performed to study the Li⁺ ionic motion and vacancy ordering in the lithium semimetal β-LiGa. The temperature dependence of the spin–lattice relaxation rate, T⁻¹₁ of the ⁷Li nuclei in the 50 atom% Li sample shows an asymmetric broad peak around 175 K and is interpreted in terms of fast Li⁺ ionic diffusion. The activation energy of hopping is estimated as 0.11 eV using a non-Debye type relaxation model. In the temperature dependence of T⁻¹₁ of the ⁷Li nuclei in 44 and 47 atom% Li samples, steep peaks are observed at 225 and 195 K, respectively. The origin of these anomalous peaks is attributed to the order–disorder transformation of Li⁺ vacancies. The temperature dependence of T⁻¹₁ of the ⁷¹Ga nuclei measured above 200 K is interpreted in terms of the relaxation originating from the fluctuation of the electric field gradient at the ⁷¹Ga nuclei due to mobile Li⁺ ions. The activation energy for the Li⁺ ionic diffusion estimated from T⁻¹₁ of the ⁷¹Ga nuclei is comparable with that obtained from T⁻¹₁ of the ⁷Li nuclei.