Formation and structure of Na2S + P2S5 amorphous materials prepared by melt-quenching and mechanical milling

xNa2S + (1 − x)P2S5 amorphous and partially crystalline materials were prepared by melt-quenching and mechanical milling. These products were characterized using x-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy. Compared to the narrower x-ray amorphous range for this system obtained through melt-quenching as found in this study, 0.50 ≤ x ≤ 0.67, the x-ray amorphous range for this system could be extended from the low-alkali ultra-thiophosphate composition of x ~ 0.25 to slightly above the high-alkali pyro-thiophosphate composition of x ~ 0.70 using mechanical milling. Mechanically milled samples with Na2S of composition x = 0.75 yielded a partially crystalline material that had diffuse XRD peaks associated to the α-Na3PS4 phase. A similar result was obtained for the x = 0.80 composition except that, as expected, it also showed peaks for unreacted (over stoichiometric) Na2S. The melt-quenched and mechanically milled samples with the same compositions 0.50 ≤ x ≤ 0.67 showed similar FT-IR and Raman spectra, indicating very similar chemical short-range structures are present in both of these amorphous materials. It was found that the Na2S + P2S5 system exhibited similar behavior to that of the Li2S + P2S5 in that chemical reaction between Na2S and P2S5 could be induced by mechanical milling near room temperature to produce both amorphous and polycrystalline materials.