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Chalcogenide glasses in the Na 2 S-GeS 2 -Ga 2 S 3 pseudoternary system were synthesized using a combination route of melt-quenching and mechanical-milling methods. First, a glass rich in germanium (90GeS 2 -10Ga 2 S 3 ) is synthesized by melt-quenching synthesis in a silica tube sealed under vacuum. This glass is used as a precursor for the second step of mechanochemistry to explore the Na 2 S-GeS 2 -Ga 2 S 3 pseudoternary system. By using this synthesis route, the glass-forming ability is improved as the vitreous domain is enlarged, especially for Na- and Ga-rich compositions. The as-obtained amorphous powders are characterized by Raman spectroscopy, differential scanning calorimetry, X-ray total scattering, and pair distribution function (PDF) analysis. The evolution of the Raman features observed is reproduced using density functional theory calculations. Impedance spectroscopy was performed to determine the conductivity of the new glasses. The addition of germanium sulfide to the Na 2 S-Ga 2 S 3 pseudobinary system enables one to increase the conductivity by 1 order of magnitude. The highest room-temperature ionic conductivity, as measured by impedance spectroscopy, is 1.8 × 10 -5 S·cm -1 .

NaGaS 2 is a newly discovered compound that has already shown great promise for a variety of applications because of its layered structure and ion exchange properties. In this work, crystalline NaGaS 2 has been synthesized by an alternative method to what has been previously published, namely, by mechanochemistry, either by a direct one-step process or by a two-step process. In the one-step process, crystalline NaGaS 2 is directly formed by milling sodium sulfide Na 2 S and gallium(III) sulfide Ga 2 S 3 . However, an amorphous material is present in majority together with the crystalline phase. In the two-step process, amorphous NaGaS 2 is first obtained by mechanical milling and then heated above its glass transition temperature to obtain a glass-ceramic mainly composed of crystalline NaGaS 2 . For the two-step process, changes of the local atomic-level structure in amorphous NaGaS 2 and after crystallization were analyzed by high-field solid-state nuclear magnetic resonance (NMR) spectroscopy as well as by X-ray total scattering and pair distribution function (PDF) analysis. Based on quantitative analysis on the 23 Na NMR spectra, modifying the annealing treatment can promote the formation of the crystalline phase up to a molar fraction of 83.8%.