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The glass transition in twinned ((phenyl)4As)2C60Cl crystals

Titelangaben

Pilz, Katrin ; Jobst, Andreas ; Lam, Erwin J. ; Lüdecke, Jens ; van Smaalen, Sander ; Bao, Jianren ; Bietsch, W. ; Schwoerer, Markus:
The glass transition in twinned ((phenyl)4As)2C60Cl crystals.
In: Zeitschrift für Kristallographie : Crystalline Materials. Bd. 217 (2002) Heft 2 . - S. 78-82.
ISSN 2196-7105
DOI: https://doi.org/10.1524/zkri.217.2.78.20629

Abstract

We have studied the crystal structures of ((phenyl)4As)2C60Cl at room temperature and below the phase transition at Tc = 1.25 K by single-crystal x-ray diffraction. At room temperature tetragonal lattice parameters were found as a = b = 12.588(1) Å and c = 20.345(1) Å. At T = 120 K the lattice parameters were determined as a = b = 12.5060(1) Å and c = 20.4420(1) Å. The room-temperature and low-temperature structures were found to be isostructural, with space group I4/m. Structure refinements were performed with restrictions on the C60 molecules according to the noncrystallographic isohedral point symmetry Ih. Derivations from this symmetry could not be found, suggesting that any possible Jahn-Teller distortion of the C60·- radical anions will be smaller than 0.01 Å. The phase transition observed in ESR at Tc = 125 K is proposed to be a glass transition. At room temperature there is dynamic disorder between two orientations of the C60 molecules as they are related by the 4-fold rotation. Below Tc the disorder becomes static. Two types of twinning have been observed in different crystals. The first type is represented by a rotation over 180° about the [1, 1, 1] axis. It results in different orientations of the 4-fold unique axes with angles of 82.4 degrees between them. Secondly, merohedral twinning was observed corresponding to the two orientations of the structure with 4/m symmetry on the tetragonal lattice. Both twinnings result in extra orientations of the C60 molecules, and they should be taken into account, when analysing the anisotropy of the physical properties of crystals of this compound.

Weitere Angaben

Publikationsform: Artikel in einer Zeitschrift
Begutachteter Beitrag: Ja
Institutionen der Universität: Fakultäten > Fakultät für Mathematik, Physik und Informatik > Fachgruppe Materialwissenschaften > Lehrstuhl Kristallographie
Fakultäten > Fakultät für Mathematik, Physik und Informatik > Fachgruppe Materialwissenschaften > Lehrstuhl Kristallographie > Lehrstuhl Kristallographie - Univ.-Prof. Dr. Sander van Smaalen
Fakultäten
Fakultäten > Fakultät für Mathematik, Physik und Informatik
Fakultäten > Fakultät für Mathematik, Physik und Informatik > Fachgruppe Materialwissenschaften
Titel an der UBT entstanden: Ja
Themengebiete aus DDC: 500 Naturwissenschaften und Mathematik > 530 Physik
Eingestellt am: 21 Mär 2016 11:17
Letzte Änderung: 05 Apr 2018 13:38
URI: https://eref.uni-bayreuth.de/id/eprint/31929