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 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".