Local structure and electrical switching in chalcogenide glasses

Bulk ${\mathrm{Al}}_x{\mathrm{As}}_{40}{\mathrm{Te}}_{60-x}$ and ${\mathrm{Al}}_x{\mathrm{As}}_{40-x}{\mathrm{Te}}_{60}$ glasses $(5\mathrm{}<~x<~20)$ are found to exhibit memory and threshold switching. ${}^{27}\mathrm{Al}$ solid-state NMR measurements reveal that in both series of glasses, Al resides in tetrahedrally (fourfold) as well as octahedrally (sixfold) coordinated environments, with the fraction of fourfold coordinated Al atoms in the glasses decreasing with Al content. Fourfold coordinated Al atoms provide structural flexibility, and promote memory switching at low Al content $\mathrm{}(x<\mathrm{}15\mathrm{}).$ At higher Al content, the growth in the fraction of sixfold coordinated atoms leads to increased network connectivity, which promotes threshold switching.