Anomalous X-ray scattering studies on superionic glassy (As 2Se 3)-(AgX) systems (X = halides)

Abstract

Anomalous X-ray scattering experiments for glassy room-temperature superionic conductors (As 2Se 3) 0.4 (AgI) 0.6 and (As 2Se 3) 0.4(AgBr) 0.6 were performed close to the As, Se, Ag, and Br K edges using a third-generation synchrotron radiation facility, ESRF. The differential structure factors, Δ iS ( Q), were obtained from detailed analyses, indicating that Δ As S( Q) and Δ Se S( Q) of both the glassy superionic semiconductors are similar to those of glassy As 2 Se 3 except the prepeak in Δ Se S( Q). The Δ Ag S( Q) spectrum of (As 2Se 3) 0.4 (AgI) 0.6 looks molten salt-like. However, the Δ Ag S( Q) of (As 2Se 3) 0.4(AgBr) 0.6 glass have quite different features from that of (As 2Se 3) 0.4 (AgI) 0.6 glass in the low Q range, and the Δ Br S( Q) has even a pre-shoulder around 13 nm − 1 unlike molten salts. In the differential pair distribution functions Δ i g( r) obtained from the Fourier transforms of Δ iS ( Q), the first peaks of Δ As g( r) and Δ Se g( r) show no correlation with those of Δ Ag g( r) and Δ Br g( r), and vice versa. From these results, it can be concluded that a pseudo-binary mixture of the As 2Se 3 network matrix and AgX-related ionic conduction pathways is a good structural model for these superionic glasses. Differences between the AgBr- and AgI mixtures were found in the second-neighbor structures around the Ag atoms, which may reflect those in the crystal structures of the AgX salts.