Infrared and terahertz studies of phase transitions in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>CH</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>NH</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>PbBr</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> perovskite
Bibliographic record
Abstract
We investigated the influence of two structural phase transitions in methylammonium lead tri-bromide ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbBr}}_{3}$ $({\mathrm{MAPbBr}}_{3})$ single crystals on the activity of polar phonons using time-domain THz transmission and far infrared (IR) reflectance spectra. The fitting using the Lorentz model of damped harmonic oscillators also enables us to determine all the polar phonon parameters, IR response functions, and their temperature dependence. The fit of the far IR spectra provides a nearly perfect quantitative description of the measured reflectance at room temperature using three phonons. On cooling, three IR active phonons of the cubic and tetragonal structures split into 15 separate bands, signaling the transformation to the orthorhombic phase below 150 K. This result is compared with the factor group analysis of the polar phonons in all three crystallographic phases. The absence of a soft optical phonon supports the previously published order-disorder character of the structural phase transitions.
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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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".