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Irradiation-driven amorphous-to-glassy transition in quartz: The crucial role of the medium-range order in crystallization

Summary

Reactive molecular dynamics simulations of neutron-like irradiation damage in α-quartz show a disordering pathway where an amorphous-to-glassy (ATG) transition emerges once medium-range order (MRO) defects appear that kinetically block crystallization upon heating. The work ties the Gupta-style distinction between glassy and amorphous solids to MRO defect percolation from short-range damage. The silica community context is nuclear waste glass and radiation-damaged minerals, where recrystallization propensity controls long-term phase stability.

Methods

RMD (LAMMPS). §II.A describes reactive molecular dynamics cascades in α-quartz with the SiO₂ reactive model referenced in the article (papers/ReaxFF_others/Anoop_Bauchy_Amorphous-Glassy-Transition2017.pdf). Each primary knock-on atom (PKA) receives 600 eV along a random direction, with Si vs O PKA selection weighted by neutron cross sections. Around each impact, a spherical NVE core hosts the ballistic cascade for ~15 ps while outer atoms remain at 300 K with a Nosé–Hoover thermostat; a variable timestep handles the violent phase, reverting to 0.5 fs otherwise. The cell then relaxes ~5 ps in NPT at 300 K and zero pressure (~20 ps total per PKA in the excerpt). Impacts repeat until enthalpy and density saturate. Supercell lattice vectors, total atom count, explicit PBC description, NPT barostat family, electric fields, and enhanced sampling are not restated in the §II.A excerpt mirrored here—confirm in pdf_path for reproduction.

Force-field training: N/A — the study applies a published SiO₂ ReaxFF parameterization cited in the article rather than reporting a new fit.

Static QM / DFT: N/A — not a DFT discovery paper; QM enters through the ReaxFF training literature.

Findings

Low deposited-energy tracks yield disordered quartz that can recrystallize on heating (with a first-order melt signature in the authors’ Gupta-style framing), whereas high deposited-energy tracks cross an amorphous-to-glassy threshold once medium-range order (MRO) defects percolate, kinetically blocking crystallization. The narrative is tied to prior irradiated silica literature (Introduction references) without reproducing benchmark tables here. Sensitivity centers on dose (deposited energy) because MRO similarity to α-quartz sets crystallization propensity. MD flux and PKA energies do not map one-to-one to reactor spectra; O diffusion between cascades and ReaxFF barrier fidelity remain model-dependent caveats unless revalidated with QM.

Limitations

The on-disk extract is partial (early sections only); ring statistics, longer annealing segments, and full parameter tables are in the full PDF (extraction_quality: partial in front matter). Cumulative damage from many PKA events can alter thermal spike overlap statistics; the stopping criterion based on enthalpy/density saturation should be read in the full methods when comparing to other irradiation codes. MRO metrics are sensitive to cooling rates after cascades; align annealing segments with the published protocol before comparing ATG thresholds across studies.

Relevance to group

Benchmark irradiation RMD methodology for silica in the PARISlab line of work (UCLA).

Citations and evidence anchors

  • DOI: 10.1103/PhysRevMaterials.1.053405.