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 TiO 6 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 TiO 6 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 SiO 4 -TiO 6 -SiO 4 -TiO 6 rings comprising TiO 6 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 SiO 4 -TiO 6 connectivity within planes nearly perpendicular to the TiO 6 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 × 10 18 α-event/g.
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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 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".