XPS valence band study of Na‐silicate glasses: energetics and reactivity
Bibliographic record
Abstract
High‐resolution X‐ray photoelectron spectroscopy (XPS) of valence bands of vitreous silica (SiO 2 (vit)), and Na‐silicate glasses are divisible into 3 sub‐bands. These are the O 2s band, the lower valence band (LVB), and the upper valence band (UVB). Many peaks of the LVB and UVB have line widths (full width at half maximum) of 1.2–1.7 eV, which are commensurate with widths of core level O 1s lines, indicating weak dispersion of these valence band peaks. Two types of oxygen exist in the glasses. There is oxygen bridging 2 Si atoms (bridging oxygen [BO]), and O bonded to Si and Na (nonbridging oxygen [NBO]). The addition of Na to siliceous glasses diminishes electronic density of states of the LVB and enhances density of states of the UVB, a consequence of quenching Si‐BO σ‐bonds of the LVB, creating Si‐NBO σ‐bonds in the UVB, and creating atomic‐like O 2p x , y nonbonding orbitals at the top of the UVB or highest occupied molecular orbitals. The process destabilizes the valence bands of the glasses by 2 to 6 eV per Si‐NBO bond formed. All orbitals are destabilized with increased Na 2 O content. There is effectively complete transfer of Na 3s electrons to NBO but this charge is redistributed among all atoms of the tetrahedron via the 4 Si‐O σ bonds (sp 3 ‐O 2p x character). The BE of the Si 2p line decreases more rapidly with Na 2 O content than any other line monitored, and this preferential accumulation of negative charge on Si causes Si‐O bonds to become weaker through decrease in the force constant of the bonds. The durability of Na‐silicate glasses decreases in response. The destabilization of the highest occupied molecular orbitals makes the Na‐rich glasses more susceptible to attack by reagents such as H + , OH − , and H 2 O. Copyright © 2017 John Wiley & Sons, Ltd.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".