Correlating structure with non-linear optical properties in xAs₄₀Se₆₀·(1 - X)As₄₀S₆₀ glasses

A series of xAs₄₀Se₆₀·(100 - x)As₄₀S₆₀ glasses, where x = 0, 25, 33, 50, 67, 75 and 100 mol% As₄₀Se₆₀, has been studied using neutron and X-ray total scattering, Raman spectroscopy and ⁷⁷Se MAS-NMR. The results are presented with measurements of non-linear refractive indices, n₂, and densities. There is no evidence for the formation of homopolar bonds in these glasses, but neutron correlation functions suggest that there is a non-random distribution of sulfur and selenium atoms in sulfur-rich glasses. The average number of sulfur atoms at a distance of 3-4 Å from a selenium atom, n_SeS, deviates from a linear variation with x in glasses containing <50 mol% As₄₀Se₆₀; n₂ for these glasses also varies non-linearly with x. Importantly, a direct comparison of n₂ and n_SeS gives a linear correlation, suggesting that n₂ may be related to the distribution of chalcogen atoms in the glasses. This journal is