X-RAY POWDER DIFFRACTION STUDY ON THE MODULATED HIGH TEMPERATURE FORMS OF SIO2 TRIDYMITE BETWEEN 110 AND 220 °C
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dc.contributor.author | Graetsch H. | |
dc.date.accessioned | 2021-03-30T10:40:26Z | |
dc.date.available | 2021-03-30T10:40:26Z | |
dc.date.issued | 2001 | |
dc.identifier | https://www.elibrary.ru/item.asp?id=872490 | |
dc.identifier.citation | Physics and Chemistry of Minerals, 2001, 28, 5, 313-321 | |
dc.identifier.issn | 0342-1791 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/27159 | |
dc.description.abstract | The crystal structure of intermediate incommensurate tridymite was refined at 150 °C from powder data. Upon cooling from above 220 °C, the basic structure with space group symmetry C2221 gradually distorted from orthorhombic to monoclinic symmetry. With decreasing temperature, the monoclinic angle γ smoothly opens up to 90.3°, while a displacive modulation with temperature-dependent wavelength develops. The 3 + 1 dimensional superspace group of the incommensurate phase is C1121ont face=symbol>aβ0). The modulation mainly consists of two sinusoidal transverse displacement waves for the silicon atoms coupled to rotations of the rigid SiO4/2trahedra. The wave vector is r=0.1192(1)a* - 0.0043(1)b* at 150 °C. Below 150 °C tridymite discontinuously transforms to another orthorhombic phase and the modulation partially locks in at the wave vector r13a*. Simultaneously, an additional incommensurate modulation with r2.0395(1)b* - 0.3882(1)c* is formed. The two-dimensional modulation does not vary significantly with the temperature. | |
dc.subject | TRIDYMITE | |
dc.subject | SILICA | |
dc.subject | INCOMMENSURATE MODULATION | |
dc.subject | DISPLACIVE PHASE TRANSITIONS | |
dc.subject | LOCK-IN | |
dc.title | X-RAY POWDER DIFFRACTION STUDY ON THE MODULATED HIGH TEMPERATURE FORMS OF SIO2 TRIDYMITE BETWEEN 110 AND 220 °C | |
dc.type | Статья |
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