Structural Modifications of Cold and Dense Cesium, Calcium, Barium, and Selenium
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Bibliographic record
Abstract
Following the development of high brilliance synchrotron x-ray sources, high density crystalline structures of elemental solids have been vastly studied at room temperature and elevated pressures. In the last decades, experimental and computational results have unveiled a vast diversity of crystalline structures adopted by many dense elements. Both complex modulated and exotic structures have been observed [1] and predicted [2]. In this communication, we report results of systematic searches for structural modifications taking place at very low temperature (T>10 K) and high pressure (P<50 GPa) in selected elementals solids. Results for cesium, calcium, barium, and selenium are presented. An extension of the known P-T phase diagram to lower temperature for cesium and selenium indicates that both elements do not adopt crystalline structures different that those already known and documented. We show that calcium at low temperature and high pressure, however, exhibits unusual and large dynamical fluctuations leading to a tetragonal distortion of the simple cubic structure known to exist at room temperature and about 30 GPa. The large amplitude fluxional behaviour leads to the appearance of a new phase, nested at T<30K between 40 and 45 GPa. Finally, barium when compressed at low temperature, transforms into a crystalline structure unobserved at high pressure and room temperature. It is found that, below 140K and in the pressure range of 13 to 35 GPa, barium does not adopt the phase IV structure, i.e., the modulated incommensurate cell, but undergoes a transition from phase II (P63/mmc) to an orthorhombic (Pmna) cell. This new structure corresponds to phase VI. On the basis of an x-ray diffraction study along quasi-isobaric and isothermal paths, we conclude that Ba-VI is most likely metastable. Our results suggest the need to scrutiny other dense elements at very low temperature. Under those conditions, unusual structural modifications are ought to be observed.
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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 | 0.001 |
| 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 it