Long-range modulation of a composite crystal in a five-dimensional superspace
- Univ. de Rennes, Rennes (France)
- Synchrotron SOLEIL, Gif-sur-Yvette cedex (France)
- Kansas State Univ., Manhattan, KS (United States)
- Dresden Univ. of Technology, Dresden (Germany)
- Eidgenossische Technische Hochschule (ETH) Zurich, Zurich (Switzerland)
The intergrowth crystal of n-tetracosane/urea presents a misfit parameter, defined by the ratio γ = ch/cg (chost/cguest), that is very close to a commensurate value (γ ≅ 1/3). High-resolution diffraction studies presented here reveal an aperiodic misfit parameter of γ = 0.3369, which is found to be constant at all temperatures studied. A complex sequence of structural phases is reported. The high temperature phase (phase I) exists in the four-dimensional superspace group P6122(00γ). At Tc1 = 179(1) K, a ferroelastic phase transition increases the dimension of the crystallographic superspace. This orthorhombic phase (phase II) is characterized by the five-dimensional (5D) superspace group C2221(00γ)(10δ) with a modulation vector ao* + cm* = ao* + δ · ch*, in which the supplementary misfit parameter is δ = 0.025(1) in host reciprocal units. Finally, this corresponds to the appearance of a modulation of very long period (about 440 ± 16 Å). At Tc2 = 163.0(5) K, a 5D to 5D phase transition leads to the crystallographic superspace group P212121(00γ)(00δ) with a very similar value of δ. This phase transition reveals a significant hysteresis effect.
- Research Organization:
- Kansas State Univ., Manhattan, KS (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC02-76SF00515; AC02-06CH11357
- OSTI ID:
- 1343611
- Alternate ID(s):
- OSTI ID: 1179707
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 91, Issue 18; ISSN 1098-0121
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Comment on Couzi et al . (2018): a phenomenological model for structural transitions in incommensurate alkane/urea inclusion compounds
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journal | August 2019 |
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