Molecular dynamics study of tridymite
| Autor: | K.J. Glaser, Robert G. Bell, C. R. A. Catlow, Akira Takada |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
Diffraction
Phase transition Materials science 02 engineering and technology 010502 geochemistry & geophysics 01 natural sciences Biochemistry tridymite Molecular dynamics Tridymite Phase (matter) General Materials Science structure skin and connective tissue diseases 0105 earth and related environmental sciences Crystallography digestive oral and skin physiology General Chemistry polymorphs 021001 nanoscience & nanotechnology Condensed Matter Physics Research Papers molecular dynamics Symmetry (physics) phase transitions QD901-999 silica Orthorhombic crystal system sense organs 0210 nano-technology Monoclinic crystal system |
| Zdroj: | IUCrJ IUCrJ, Vol 5, Iss 3, Pp 325-334 (2018) |
| ISSN: | 2052-2525 |
| Popis: | Polymorphic structural changes in tridymite have been investigated by molecular dynamics simulation. The main polymorphic transitions were reproduced and their mechanisms are explained. 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. |
| Databáze: | OpenAIRE |
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