Structure and Ionic Conductivity of Halocomplexes of Main Group Metallic Elements Studied by NMR and NQR

Abstract

Li₃InBr₆ undergoes phase transition to a lithium superionic conductor at T _tr = 314 K (σ = 5.0 × 10⁻⁴ S cm⁻¹ at 330 K). The Rietveld analysis and the DSC measurement suggested that the positional disorder is introduced at the cationic sites above T _tr. The X-ray powder diffraction pattern at the superionic phase changes gradually with temperature and finally shows a simple powder pattern at 420 K which is quite similar to that of LiBr. This rock salt structure contains intrinsic vacancies because one In³⁺ and two vacancies substitute for three Li⁺. ⁷Li and ¹¹⁵In NMR support the rapid diffusion of the Li⁺ and the introduction of the In³⁺ into the rock salt structure. On the other hand, the ionic conductivity for Na₃InCl₆ was 10⁻⁵ S cm⁻¹ even at 500 K. Conduction path for the sodium ions could be proposed by means of the Rietveld analysis and the NMR experiment using a single crystal.