Elasticity and high-pressure behavior of Mg2Cr2O5 and CaTi2O4-type phases of magnesiochromite and chromite
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Bibliographic record
Abstract
Abstract In situ high-pressure and high-temperature X-ray diffraction studies on magnesiochromite, MgCr2O4, and a natural chromite, (Mg,Fe)(Al,Cr)2O4, using a laser-heated diamond-anvil cell technique were performed at pressures to ~45 GPa. Our results on MgCr2O4 at ~15 GPa showed temperature-induced dissociation of MgCr2O4 to Cr2O3+MgO below ~1500 K and formation of modified ludwigite (mLd)-type Mg2Cr2O5+Cr2O3 above ~1500 K. Above 20 GPa, only a single phase with the CaTi2O4-type structure of MgCr2O4 was observed at 1400–2000 K. A second-order Birch-Murnaghan fit to pressure-volume data for the CaTi2O4-type phase of MgCr2O4 yields zero-pressure volume (V0) = 264.4(8) Å3 and bulk modulus (K0) = 185.4(4) GPa, and for the CaTi2O4-type structure of natural (Mg,Fe)(Al,Cr)2O4 yields V0 = 261(1) Å3 and K0 = 175.4(2) GPa. A second-order Birch-Murnaghan fit to pressure-volume data of mLd-type Mg2Cr2O5 yields V0 = 338.9(8) Å3 and K0 = 186.5(6) GPa. The obtained high-pressure phase relations of chromite spinels can be used as an indicator for shock pressure in impact rocks and meteorites. The bulk moduli of the high-pressure phases of MgCr2O4 and FeCr2O4 can help develop a thermodynamic model for Mg and Fe end-member spinels in the upper mantle and transition zone.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.002 |
| 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 it