Mechanochemical Synthesis and Study of the Local Structure of NaGaS 2 Glass and Glass-Ceramics.

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%.