Hydrogen Motion in Magnesium Hydride by NMR
Bibliographic record
Abstract
In coarse-grained MgH 2, the diffusive motion of hydrogen remains too slow (<10 5 hops s −1 ) to narrow the H NMR line up to 400 °C. Slow-motion dipolar relaxation time T 1D measurements reveal the motion, with hopping rate ω H from 0.1 to 430 s −1 over the range of 260 to 400 °C, the first direct measurement of H hopping in MgH 2 . The ω H data are described by an activation energy of 1.72 eV (166 kJ/mol) and attempt frequency of 2.5 × 10 15 s −1 . In ball-milled MgH 2 with 0.5 mol % added Nb 2 O 5 catalyst, line-narrowing is evident already at 50 °C. The line shape shows distinct broad and narrow components corresponding to immobile and mobile H, respectively. The fraction of mobile H grows continuously with temperature, reaching ∼30% at 400 °C. This demonstrates that this material’s superior reaction kinetics are due to an increased rate of H motion, in addition to the shorter diffusion paths from ball-milling. In ball-milled MgH 2 without additives, the line-narrowed component is weaker and is due, at least in part, to trapped H 2 gas. The spin−lattice relaxation rates T 1 −1 of all materials are compared, with ball-milling markedly increasing T 1 −1 . The weak temperature dependence of T 1 −1 suggests a mechanism with paramagnetic relaxation centers arising from the mechanical milling.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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".