Structure and composition of surface depletion layers in poled aluminosilicate glasses
Bibliographic record
Abstract
Abstract Thermal poling processes can be used to form modified surface layers on glass that, under ion‐blocking electrode conditions, are depleted of virtually all network‐modifying cations relative to the network‐forming species. During this process, many outstanding questions remain as to the structure of these layers and how it may vary between glasses of different “parent” composition, with important implications for resultant surface properties and industrial applications of this technology. This phenomenon of depleting modifiers is particularly difficult to rationalize in aluminosilicate glass compositions, where—in the parent glass—aluminum ions are predominantly present as cation‐charge‐compensated [AlO4] − tetrahedra prior to poling. Here, we present results of a detailed investigation into the surface depletion layers formed across a wide range of ternary sodium aluminosilicate (NAS) glasses, applying a host of surface‐sensitive spectroscopy methods to directly interrogate the resulting composition and structure within the Na‐depleted, anode‐side surface layers. The desired depletion layers were successfully formed on all of the NAS glasses attempted, all showing (a) near‐complete depletion of alkali within 300‐500 nm‐thick layers on the anode‐side surfaces, (b) thin zones of Al depletion with the Na‐depleted layer, and (c) the absence of injected H + ions that could serve as an alternative charge‐compensation mechanism. These data essentially confirmed a true binary Al 2 O 3 –SiO 2 composition inside the depletion layers. However, no significant structural dependence was found as a function of parent glass, where initial compositions ranged from peralkaline to charge‐balanced. Importantly, TEM imaging showed the depletion layers to be fully amorphous and homogeneous (not phase‐separated) at the nanoscale, despite final compositions in the range of 5‐33 mol% Al 2 O 3 —a composition space notoriously prone to phase‐separation if prepared by conventional melting. Within the depletion layers, ELNES and TEY‐XANES evidence is shown for retention of Al in a 4‐coordinated state, along with XPS data indicating elimination of non‐bridging oxygen. Taken as a whole, our results indicate a highly‐connected aluminosilicate network, most likely with a relatively high concentration of 3‐coordinated oxygen—or O “triclusters”—as a plausible means of charge‐compensating 4‐coordinated Al in the absence of Na + or H + . The combined results of this work provide convincing new evidence for unique glass structures within the depletion layers not achievable through analogous melt pathways, with important implications for surface properties.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 teacher head, 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".