Title:
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Structure and reorientational dynamics of 1-F-adamantane
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Author:
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Ben Hassine, Bacem; Negrier, Philippe; Romanini, Michela; Barrio Casado, María del; Macovez, Roberto; Kallel, A.; Mondieig, Denise; Tamarit Mur, José Luis
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Other authors:
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Universitat Politècnica de Catalunya. Departament de Física; Universitat Politècnica de Catalunya. GCM - Grup de Caracterització de Materials |
Abstract:
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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 |
Abstract:
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Peer Reviewed |
Subject(s):
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-Àrees temàtiques de la UPC::Física::Física molecular -Àrees temàtiques de la UPC::Enginyeria química::Química física -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 |
Rights:
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http://creativecommons.org/licenses/by-nc-nd/3.0/es/ |
Document type:
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Article - Published version Article |
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