Unexpected role of metal halides in a chalcogenide glass network

Abstract

Chalcogenide glasses containing light alkali and Group 11 (Cu, Ag) halides MY (Y = Cl, Br, I) exhibit high ionic conductivity while their heavy alkali counterparts show promising properties for optical applications. The structural role of metal halides in chalcogenide glass networks remains either essentially unknown (alkali halides) or controversial (CuY, AgY). In addition, possible structural changes as a function of MY content have not been reported. Using pulsed neutron diffraction, high-energy X-ray scattering, Raman spectroscopy and FPMD modeling, we show unexpected role of silver halides as unconventional modifiers taking two contrasting glass compositions: (AgI)0.1(As2S3)0.9 (critical percolation domain) and (AgBr)0.5(As2S3)0.5 (modifier-controlled region) as an example. The latter alloy seems to be a promising precursor for thermoelectric applications. The deep insight into the glass structure on the short- and intermediate-range scale, including an enhanced chemical disorder, enables a rational design of these functional materials.