Irradiation- vs. vitrification-induced disordering: The case of α-quartz and glassy silica
Summary¶
Radiation damage and melt quenching both produce disordered silica networks, but it is not obvious whether the two routes converge to the same amorphous structure or whether irradiation can be mapped onto the glassy end state of vitrification. This Journal of Chemical Physics article addresses that question using reactive molecular dynamics (RMD) to compare the atomic structure of neutron-irradiated α-quartz with a glassy silica reference obtained by vitrification. The abstract states that although some similarity exists between the two disordered states, their structures differ at both short range (below about 3 Å) and medium range (between about 3 Å and 10 Å). In particular, the irradiated quartz network retains coordination defects, edge-sharing motifs, and large rings that are absent from the glassy silica model in their comparison. The work is motivated by applications where quartz and silica glass are exposed to ionizing radiation, including concrete aggregates in nuclear installations and optical components, and it frames irradiation-induced disorder as structurally distinct from quenched melt disorder rather than as a simple subset of the same amorphous state.
Methods¶
RMD irradiation (LAMMPS). §II.A of J. Chem. Phys. 146, 204502 (papers/ReaxFF_others/Anoop_Mathieu_SiO2_radiation_defects.pdf) follows established RMD practice: a random α-quartz atom becomes a 600 eV PKA along a random direction, with Si vs O selection weighted by neutron cross sections. LAMMPS integrates the ballistic cascade inside an NVE sphere of radius 20 Å while exterior atoms are thermostatted to absorb phonons without damping the core cascade (the thermostat family is not named in the p1–2 extract). PBC apply to the quartz supercell; lattice metrics, baseline timestep, total duration after each impact, electric fields, and enhanced sampling are not recovered from the indexed extract—read pdf_path. NPT relaxations at 300 K and zero pressure may appear after cascades in the full article; the barostat model is not confirmed from the excerpt alone.
Glass reference. A glassy silica counterpart is generated by melt quench (vitrification) at high temperature followed by quench, per Methods in the same issue; the explicit quench rate is not in the indexed extract.
Structural comparison. The paper contrasts short- and medium-range metrics (ring statistics, coordination environments, etc.) between irradiated quartz and the vitreous reference.
Force-field training: N/A — uses the same SiO₂ ReaxFF framework as the authors’ related irradiation work; no new parameterization is the focus here.
Static QM / DFT: N/A — not a standalone DFT production study in the excerpted Methods opening.
Findings¶
Irradiation and vitrification yield non-equivalent disordered silica networks: irradiated α-quartz retains coordination defects, edge-sharing motifs, and large rings absent from the glassy silica benchmark in their analysis, so irradiation disorder is not a simple subset of melt-quenched glass. Mechanistic distinctions appear at both short (<3 Å) and medium (~3–10 Å) range, as summarized in the abstract. Compared side-by-side under the authors’ protocols, the two preparation routes therefore probe different disorder structures at the same composition. Sensitivity to pathway (PKA cumulative damage vs. quench rate in the vitreous reference) is the main lever in the conclusions. Limitations include ReaxFF bias in barrier heights and ring statistics, discussed in the article’s Discussion. Finer ring distributions and extended annealing checks should be read from the full PDF rather than this short extract.
Limitations¶
The local repository extract covers the abstract and the start of Methods; quantitative ring distributions, full thermalization protocols after cascades, and convergence checks should be taken from the full PDF (extraction_quality: partial). Reactive force fields trade accuracy for tractability; barrier heights and defect populations are model-dependent.
Relevance to group¶
Benchmark for comparing radiation-damaged quartz with glassy silica within reactive MD, relevant to nuclear materials and oxide glass science.
Citations and evidence anchors¶
- DOI:
10.1063/1.4982944.