Atomic and electronic structures of amorphousGe2Sb2Te5; melt-quenched versus ideal glasses

Abstract

To investigate an amorphous structure ofGe2Sb2Te5 that satisfiesthe 8-N rule (so-called ‘ideal glass’), we perform alternative melt-quench simulations onSi2As2Se5 andreplace atoms in the final structure with Ge–Sb–Te. The resulting structures have salient features of the8-N rule such as the tetrahedral configuration for all Ge atoms and the localized Te lone pairsat the valence top. In addition, the average Ge–Te and Sb–Te distances are in goodagreement with experiment. The energetic stability of the ideal glass supports theexistence of this amorphous structure that is distinct from the melt-quenchedglass. From the analysis of electronic structures and optical dielectric constants,it is concluded that the electronic character of the melt-quenched amorphousGe2Sb2Te5 lies in between the resonant p-bonding of the crystalline phase and the covalent bonding ofthe ideal glass.