The Ideal Crystal Structure of Cristobalite X-I: A Bridge in SiO2 Densification
| Autor: | Eva Zurek, Jesse S. Smith, Przemyslaw Dera, Hannah Shelton, Tiange Bi |
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| Rok vydání: | 2018 |
| Předmět: | |
| Zdroj: | The Journal of Physical Chemistry C. 122:17437-17446 |
| ISSN: | 1932-7455 1932-7447 |
| Popis: | On compression of α-cristobalite SiO2 to pressures above approximately 12 GPa, a new polymorph known as cristobalite X-I forms. The existence of cristobalite X-I has been known for several decades; however, consensus regarding its exact atomic arrangement has not yet been reached. The X-I phase constitutes an important step in the silica densification process, separating low-density tetrahedral framework phases from high-density octahedral polymorphs. It is the only nonquenchable high-density SiO2 phase, which reverts to the low-density form on decompression at ambient temperature. Recently, an experimental study proposed an octahedral model of SiO2 X-I with intrinsic structural defects involving partial Si site occupancies. In contrast, our new single-crystal synchrotron X-ray diffraction experiments have shown that the ideal structure of this phase should instead be described by a defect-free model, which does not require partial occupancies. The structure of cristobalite X-I consists of octahedral chai... |
| Databáze: | OpenAIRE |
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