title: Network topology for the formation of solvated electrons in binary CaO-Al2O3 composition glasses.
abstract: Glass formation in the CaO-Al2O3 system represents an important phenomenon because it does not contain typical network-forming cations. We have produced structural models of CaO-Al2O3 glasses using combined density functional theory-reverse Monte Carlo simulations and obtained structures that reproduce experiments (X-ray and neutron diffraction, extended X-ray absorption fine structure) and result in cohesive energies close to the crystalline ground states. The O-Ca and O-Al coordination numbers are similar in the eutectic 64 mol % CaO (64CaO) glass [comparable to 12CaO·7Al2O3 (C12A7)], and the glass structure comprises a topologically disordered cage network with large-sized rings. This topologically disordered network is the signature of the high glass-forming ability of 64CaO glass and high viscosity in the melt. Analysis of the electronic structure reveals that the atomic charges for Al are comparable to those for Ca, and the bond strength of Al-O is stronger than that of Ca-O, indicating that oxygen is more weakly bound by cations in CaO-rich glass. The analysis shows that the lowest unoccupied molecular orbitals occurs in cavity sites, suggesting that the C12A7 electride glass [Kim SW, Shimoyama T, Hosono H (2011) Science 333(6038):71-74] synthesized from a strongly reduced high-temperature melt can host solvated electrons and bipolarons. Calculations of 64CaO glass structures with few subtracted oxygen atoms (additional electrons) confirm this observation. The comparable atomic charges and coordination of the cations promote more efficient elemental mixing, and this is the origin of the extended cage structure and hosted solvated (trapped) electrons in the C12A7 glass.
authors.affiliation: Department of Physics, Tampere University of Technology, FI-33101 Tampere, Finland.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Akola
authors.forename: Shinji
authors.initials: S
authors.lastname: Kohara
authors.forename: Koji
authors.initials: K
authors.lastname: Ohara
authors.forename: Akihiko
authors.initials: A
authors.lastname: Fujiwara
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Atsunobu
authors.initials: A
authors.lastname: Masuno
authors.forename: Takeshi
authors.initials: T
authors.lastname: Usuki
authors.forename: Takashi
authors.initials: T
authors.lastname: Kubo
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nakahira
authors.forename: Kiyofumi
authors.initials: K
authors.lastname: Nitta
authors.forename: Tomoya
authors.initials: T
authors.lastname: Uruga
authors.forename: J K Richard
authors.initials: JK
authors.lastname: Weber
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Benmore
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D001672:Biocompatible Materials / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D004583:Electrons; D005898:Glass / Q000737:chemistry*; D008422:Materials Testing; D009010:Monte Carlo Method; D010100:Oxygen / Q000737:chemistry; D058989:Vitrification
chemical_list: D001672:Biocompatible Materials; D002412:Cations; D000537:Aluminum Oxide; D010100:Oxygen
keywords: amorphous network; electron localization; glass topology