Multinuclear Magnetic Resonance Tracking of Hydro, Thermal, and Hydrothermal Decomposition of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>
Bibliographic record
Abstract
An NMR investigation of methylammonium lead iodide, the leading member of the hybrid organic–inorganic perovskite class of materials, and of its putative decomposition products as a result of exposure to heat and humidity, has been undertaken. We show that the 207 Pb NMR spectra of the compound of interest and of the proposed lead-containing decomposition products, CH 3 NH 3 PbI 3 ·H 2 O, (CH 3 NH 3 ) 4 PbI 6 ·2H 2 O, and PbI 2, have distinctive chemical shifts spanning over 1400 ppm, making 207 Pb NMR an ideal tool for investigating this material; further information may be gained from 13 C and 1 H NMR spectra. As reported in many investigations of CH 3 NH 3 PbI 3 on films, the bulk material hydrates in the presence of high relative humidity (approximately 80%), yielding the monohydrated perovskite CH 3 NH 3 PbI 3 ·H 2 O. This reaction is reversible by heating the sample to 341 K. We show that neither (CH 3 NH 3 ) 4 PbI 6 ·2H 2 O nor PbI 2 is observed as a decomposition product and that, in contrast to many studies on CH 3 NH 3 PbI 3 films, the bulk material does not decompose or degrade beyond CH 3 NH 3 PbI 3 ·H 2 O upon prolonged exposure to humidity at ambient temperature. However, exposing CH 3 NH 3 PbI 3 concurrently to heat and humidity, or directly exposing it to liquid water, leads to the irreversible formation of PbI 2 . In spite of its absence among the decomposition products, the response of (CH 3 NH 3 ) 4 PbI 6 ·2H 2 O to heat was also investigated. It is stable at temperatures below 336 K but then rapidly dehydrates, first to CH 3 NH 3 PbI 3 ·H 2 O and then to CH 3 NH 3 PbI 3 . The higher stability of the bulk material as reported here is a promising advance, since stability is a major concern in the development of commercial applications for this material.
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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".