Takada, A;
Glaser, KJ;
Bell, RG;
Catlow, CRA;
(2018)
Molecular dynamics study of tridymite.
IUCrJ
, 5
(3)
pp. 325-334.
10.1107/S2052252518004803.
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Abstract
Structural changes in tridymite have been investigated by molecular dynamics simulation. Two thermal processes were carried out, one cooling from the high-temperature hexagonal structure of tridymite (HP-tridymite) and the other heating from the low-temperature monoclinic structure of tridymite (MX1-tridymite). The former process showed that HP, LHP (low-temperature hexagonal structure), OC (orthorhombic structure with C222₁ symmetry) and OP (orthorhombic structure with P2₁2₁2₁ symmetry)-like structures appeared in sequence. In contrast, the latter process showed that MX1, OP, OC, LHP and HP-like structures appeared in sequence. Detailed analysis of the calculated structures showed that the configuration underwent stepwise changes associated with several characteristic modes. First, the structure of HP-tridymite determined from diffraction experiments was identified as a time-averaged structure in a similar manner to β-cristobalite, thus indicating the important role of floppy modes of oxygen atoms at high temperature – one of the common features observed in silica crystals and glass. Secondly, the main structural changes were ascribed to a combination of distortion of the six-membered rings in the layers and misalignment between layers. We suggest that the slowing down of floppy oxygen movement invokes the multistage emergence of structures with lower symmetry on cooling. This study therefore not only reproduces the sequence of the main polymorphic transitions in tridymite, except for the appearance of the monoclinic phase, but also explains the microscopic dynamic structural changes in detail.
| Type: | Article |
|---|---|
| Title: | Molecular dynamics study of tridymite |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1107/S2052252518004803 |
| Publisher version: | http://dx.doi.org/10.1107/S2052252518004803 |
| Language: | English |
| Additional information: | © 2018 International Union of Crystallography. This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence (https://creativecommons.org/licenses/by/2.0/uk/legalcode). |
| Keywords: | silica, tridymite, molecular dynamics, structure, phase transitions, polymorphs |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10048799 |
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