Preparation and Structure of the Ion-Conducting Mixed Molecular Glass Ga2I3.17

Modern functional glasses have been prepared from a wide range of precursors, combining the benefits of their isotropic disordered structures with the innate functional behavior of their atomic or molecular building blocks. The enhanced ionic conductivity of glasses compared to their crystalline counterparts has attracted considerable interest for their use in solid-state batteries. In this study, we have prepared the mixed molecular glass Ga₂I_3.17 and investigated the correlations between the local structure, thermal properties, and ionic conductivity. The novel glass displays a glass transition at 60 °C, and its molecular make-up consists of GaI₄^– tetrahedra, Ga₂I₆^2– heteroethane ions, and Ga⁺ cations. Neutron diffraction was employed to characterize the local structure and coordination geometries within the glass. Raman spectroscopy revealed a strongly localized nonmolecular mode in glassy Ga₂I_3.17, coinciding with the observation of two relaxation mechanisms below T_g in the AC admittance spectra.

The structure of the new ion-conducting glass with composition Ga₂I_3.17 features gallium in three oxidation states, as Ga⁺ ions are coordinated by Ga₂I₆²⁻ heteroethane and GaI₄⁺ molecular ions. A localized non-molecular mode was observed in Raman spectroscopy, which loses intensity above the glass transition at 60 °C. AC admittance spectra show a concomitant change in the relaxation mechanism. The ionic conductivity of Ga₂I_3.17 is strongly enhanced in the glassy versus crystalline state.