Diffusion of protons and sodium ions in silicophosphate glasses: insight based on first-principles molecular dynamic simulations

Abstract

We propose a microscopic diffusion mechanism of protons and Na+ ions in phosphate glasses using first-principles molecular dynamic simulations.

Anhydrous Silicophosphoric Acid Glass: Thermal Properties and Proton Conductivity

“…In H 5 Si 2 P 9 O 29 glass, only protons that bind to the NBOs of PO 4 units surrounding Si (6) atoms (i. e., Q 3 (1Si) units) and form O−H bonds can be involved in charge compensation. Thus, the protons bound to Q 3 (1Si) units are strongly trapped by the negative charges of (SiO 6/2 ) 2− by Coulombic attraction, and a large energy barrier must be overcome for these protons to migrate to other PO 4 units, which is consistent with a prediction from a first‐principles molecular dynamics simulation [33] . Because a large proportion of PO 4 units in H 5 Si 2 P 9 O 29 glass form Q 3 (1Si) units, it is not possible for protons to migrate long distances without passing through a Q 3 (1Si) unit, as indicated by the blue dashed arrow in Figure 4a (the corresponding variation in the potential energy of the proton carrier along this migration pathway is schematically shown in Figure 4b).…”

“…Thus, the protons bound to Q 3 (1Si) units are strongly trapped by the negative charges of (SiO 6/2 ) 2À by Coulombic attraction, and a large energy barrier must be overcome for these protons to migrate to other PO 4 units, which is consistent with a prediction from a firstprinciples molecular dynamics simulation. [33] Because a large proportion of PO 4 units in H 5 Si 2 P 9 O 29 glass form Q 3 (1Si) units, it is not possible for protons to migrate long distances without passing through a Q 3 (1Si) unit, as indicated by the blue dashed arrow in Figure 4a (the corresponding variation in the potential energy of the proton carrier along this migration pathway is schematically shown in Figure 4b). Thus, compared to common proton-conducting phosphate glasses, H 5 Si 2 P 9 O 29 glass requires a relatively large E a for proton conduction and exhibits a small μ H .…”

Structure and dissolution of silicophosphate glass

“…

glasses are promising therapeutic ion-releasing materials. Herein, we investigated the state of silicon (Si) in P 2 O 5 -SiO 2 -Na 2 O-CaO glass using a model with a composition of 55.0P 2 O 5 -21.3SiO 2 -23.7Na 2 O (mol%), incorporating a six-fold-coordinated silicon structure ( [6] Si). The model was constructed using a classical molecular dynamics method and relaxed using the first-principles method.Further, we experimentally prepared glasses, substituting Na 2 O for CaO, to investigate the dissolution of glass with varying [6] Si and PO 4 tetrahedra (Q P n ) distributions (n = number of bridging oxygens (BOs) to neighboring tetrahedra).

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“…The model was constructed using a classical molecular dynamics method and relaxed using the first-principles method.Further, we experimentally prepared glasses, substituting Na 2 O for CaO, to investigate the dissolution of glass with varying [6] Si and PO 4 tetrahedra (Q P n ) distributions (n = number of bridging oxygens (BOs) to neighboring tetrahedra). [6] Si in the glass model preferentially coordinated with Q P 3 . When Si was surrounded by phosphate groups, phosphorus (P) induced the formation of [6] Si by elongating the Si-O distance, and [6] Si acted like a glass network former (NWF).…”

“…[6] Si in the glass model preferentially coordinated with Q P 3 . When Si was surrounded by phosphate groups, phosphorus (P) induced the formation of [6] Si by elongating the Si-O distance, and [6] Si acted like a glass network former (NWF). Na + coordinated with [6] Si-O-P bonds via electrostatic interactions with BO.…”