Spontaneous Reactivity of La<sub>2</sub>CuO<sub>4</sub> toward CO<sub>2</sub> Diagnosed Using Variable Temperature Raman Spectroscopy
Bibliographic record
Abstract
Raman spectroscopic measurements on a series of perovskites as a function of the temperature and gaseous atmosphere reveal chemical reactions between CO 2 and La 2 CuO 4 that alter the thermal phase transitions and inhibit the synthesis of pristine La 2 CuO 4 . Variable temperature Raman spectra acquired under O 2 environments show that La 2 CuO 4 synthesized under ambient conditions undergoes not only the two previously documented phase transitions but also a loss of Raman vibrations at ca. 200 °C that we attribute to desorption of chemisorbed CO 2 . Samples heated to 700 °C and then cooled to room temperature under O 2 show a Raman spectrum with many fewer peaks; subsequent exposure to CO 2 at room temperature reveals a spontaneous surface reaction through an increased number of peaks in the spectrum. A subsequent heat ramp under CO 2 shows desorption of the additional CO 2 -related peaks, a ca . 50 °C change in temperature for the two thermal phase transitions, and signs of La 2 O 2 (CO 3 ) formation at temperatures above 538 °C. The original La 2 CuO 4 spectrum is obtained only after heating in the presence of CO 2, which suggests that synthesis under ambient conditions leads to incorporation of CO 2 into the structure. Partial substitution of Ni for Cu to obtain La 2 Cu 0.9 Ni 0.1 O 4 facilitates manipulation of oxygen vacancies in the lattice by heating in oxygen deficient or rich atmospheres but also prevents thermal phase transitions and inhibits direct reactions with CO 2 . We attribute both features to strengthened bonds between B-site cations and oxygen, which significantly alters chemical reactivity. We anticipate that in situ variable temperature Raman spectroscopy will be an effective tool for exploring chemical reactivity and guide synthetic protocol development for solid state materials.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".