Reverse Monte Carlo modeling of Ge-As-Te chalcogenide glass system

Abstract

Chalcogenide glasses are well known for their wide technological applications due to their optical, structural and electrical properties. Their wide-ranging applications can be stated as infrared optical fibers, optical elements, switching and memory devices because of their low phonon energy and optical losses, good thermal and chemical stability and infrared transparency. In this thesis, three dimensional structures of GexAs2xTe100-3x glasses with total metal contents (Ge+As) of 30, 40, 50, and 70 at.% were generated by employing reverse Monte Carlo modeling based on high energy x-ray diffraction data from the literature. Short- and intermediate-range structural characteristics are elucidated based on these models. Structural parameters involving coordination numbers, partial structure factors, partial pair distribution functions, bond angle distributions and ring size distributions are obtained and evaluated to reveal the atomic structures of these materials. It was found that Ge, As, and Te atoms were 4, 3, and 2, coordinated respectively, independent of chemical composition. Increasing metal (Ge+As) content in the system resulted in the appearance of first sharp diffraction peak (FSDP) in the structure factors that indicate the presence of intermediate-range order in the system. Ring size distributions for glasses with low metal contents (3x=30 and 40) revealed a very narrow distribution whereas increasing metal content resulted in much wider ring size distributions that might be correlated with the development of intermediate range order.