Monitoring and Understanding the Paraelectric–Ferroelectric Phase Transition in the Metal–Organic Framework [NH<sub>4</sub>][M(HCOO)<sub>3</sub>] by Solid‐State NMR Spectroscopy
Bibliographic record
Abstract
The paraelectric-ferroelectric phase transition in two isostructural metal-organic frameworks (MOFs) [NH4 ][M(HCOO)3 ] (M=Mg, Zn) was investigated by in situ variable-temperature (25) Mg, (67) Zn, (14) N, and (13) C solid-state NMR (SSNMR) spectroscopy. With decreasing temperature, a disorder-order transition of NH4 (+) cations causes a change in dielectric properties. It is thought that [NH4 ][Mg(HCOO)3 ] exhibits a higher transition temperature than [NH4 ][Zn(HCOO)3 ] due to stronger hydrogen-bonding interactions between NH4 (+) ions and framework oxygen atoms. (25) Mg and (67) Zn NMR parameters are very sensitive to temperature-induced changes in structure, dynamics, and dielectric behavior; stark spectral differences across the paraelectric-ferroelectric phase transition are intimately related to subtle changes in the local environment of the metal center. Although (25) Mg and (67) Zn are challenging nuclei for SSNMR experiments, the highly spherically symmetric metal-atom environments in [NH4 ][M(HCOO)3 ] give rise to relatively narrow spectra that can be acquired in 30-60 min at a low magnetic field of 9.4 T. Complementary (14) N and (13) C SSNMR experiments were performed to probe the role of NH4 (+) -framework hydrogen bonding in the paraelectric-ferroelectric phase transition. This multinuclear SSNMR approach yields new physical insights into the [NH4 ][M(HCOO)3 ] system and shows great potential for molecular-level studies on electric phenomena in a wide variety of MOFs.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.002 |
| 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".