Structure and reorientational dynamics of 1-F-adamantane
The polymorphism and the dynamics of a simple rigid molecule (1-fluoro-adamantane) have been studied by means of X-ray powder diffraction and broadband dielectric spectroscopy. At temperatures below the melting point, the molecule forms an orientationally disordered Phase I with a cubic-centered str...
| Autores: | , , , , , , , |
|---|---|
| Tipo de recurso: | artículo |
| Fecha de publicación: | 2016 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/89251 |
| Acceso en línea: | https://hdl.handle.net/2117/89251 https://dx.doi.org/10.1039/c6cp01144f |
| Access Level: | acceso abierto |
| Palabra clave: | Glass transition temperature Adamantane Supercooled liquids Polymorphism (Crystallography) Molecular dynamics glass-transition supercooled liquids molecular motions plasic phase 1-fluoroadamantane relaxation adamantane crystals polimorphism temperature Vidre -- Propietats físiques Líquids -- Propietats tèrmiques Polimorfisme Dinàmica molecular Àrees temàtiques de la UPC::Física::Física molecular Àrees temàtiques de la UPC::Enginyeria química::Química física |
| Sumario: | The polymorphism and the dynamics of a simple rigid molecule (1-fluoro-adamantane) have been studied by means of X-ray powder diffraction and broadband dielectric spectroscopy. At temperatures below the melting point, the molecule forms an orientationally disordered Phase I with a cubic-centered structure (Phase I, Fm (3) over barm, Z = 4). This phase possesses eight equilibrium positions for the fluorine atom, with equal occupancy factors of 1/8. A solid-solid phase transition to a low-temperature tetragonal phase (Phase II, P (4) over bar2(1)c, Z = 2) reduces the statistical disorder to only four possible equivalent sites for the fluorine atom, with fractional occupancies of 1/4. The dynamics has been rationalized under the constraints imposed by the space group of the crystal structure determined by powder X-ray diffraction. The dielectric spectroscopy study reveals that the statistical disorder in Phase II is dynamic in character and is associated with reorientational jumps along the two-and three-fold axes. In the dielectric loss spectra, the cooperative (alpha) relaxation exhibits a shoulder on the high-frequency side. This remarkable finding clearly reveals the existence of two intrinsic reorientational processes associated with the exchange of the F atom along the four sites. In addition to such |
|---|