Structural anisotropy and annealing-induced nanoscale atomic rearrangements in metamict titanite
Bibliographic record
Abstract
The structural state of metamict titanite was studied by Raman spectroscopy, complementary high-resolution transmission electron microscopy, and single-crystal X-ray diffraction. The results show that Raman scattering collected from metamict titanite is highly anisotropic, which is typical of single crystals. But surprisingly, the observed Raman-scattering dependence on the sample orientation is much more pronounced for heavily metamict than for weakly metamict titanite samples. These radiation-induced anisotropic effects are related to the specific atomic arrangements in metamict titanite. The Raman spectra collected in backscattering geometry from a plane nearly perpendicular to the chains of corner-sharing TiO6 octahedra arise predominantly from phonon modes in crystalline nanoregions with radiation-induced defects, whereas the contribution of atomic vibrations in radiation-induced amorphous nanoregions is better pronounced in the Raman spectra collected from a plane containing TiO6 chains. This difference provides a unique opportunity to study separately, the structural transformations of the crystalline and amorphous fractions in metamict titanite. The results show that the radiation-induced periodic faults in the crystalline matrix are related to the disturbance of SiO4-TiO6-SiO4-TiO6 rings comprising TiO6 octahedra from different chains, whereas the radiationinduced amorphization is related to the partial change of Ti coordination from octahedral to pyramidal and/or tetrahedral, which in turn violates the Ti-O-Ti intrachain linkages. This indicates that the plane containing Si-O-Ti-O bond rings is less susceptible to a self-accumulation of radiation-induced defects resulting in the development of amorphous regions as compared to the perpendicular plane containing Ti-O bond chains. Sample-orientation-dependent Raman spectroscopy was further applied to annealed metamict titanite to give further insight into the temperature-driven recovery processes in the crystalline and amorphous nanoregions. Multistep annealing by 50 K for 2 h per step gradually suppresses the structural defects in the crystalline fraction as the improvement of the SiO4-TiO6 connectivity within planes nearly perpendicular to the TiO6 chains reaches saturation near 900 K. The annealing-induced recrystallization of the radiation-induced amorphous nanoregions takes place in the temperature range between approximately 650 and 950 K, with a maximum near 750 K. Raman scattering shows that multistep annealing up to 1173 K is insufficient to recover the crystalline structure of the studied metamict titanite sample, which has an accumulated radiation dose of 1.2 × 1018 α-event/g.
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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".