Amorphous to amorphous insulator-metal transition in GeSe3:Ag glasses

Abstract

We study an insulator-metal transition in a ternary chalcogenide glass (GeSe3)1-xAgx for x=0.15 and 0.25. The conducting phase of the glass is obtained by using gap sculpting [Prasai, Sci. Rep. 5, 15522 (2015)2045-232210.1038/srep15522] and it is observed that the metallic and insulating phases have nearly identical density functional energies but have a conductivity contrast of ∼108. As such, we demonstrate an example of polyamorphism for which energetically close phases exhibit dramatically different optical properties. The transition from insulator to metal involves growth of an Ag-rich phase accompanied by a depletion of tetrahedrally bonded Ge(Se1/2)4 in the host network. The relative fraction of the amorphous Ag2Se phase and GeSe2 phase is shown to be a critical determinant of dc conductivity.