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Title: Long-range modulation of a composite crystal in a five-dimensional superspace

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.
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5] ;  [3] ;  [1]
  1. Univ. de Rennes, Rennes (France)
  2. Synchrotron SOLEIL, Gif-sur-Yvette cedex (France)
  3. Kansas State Univ., Manhattan, KS (United States)
  4. Dresden Univ. of Technology, Dresden (Germany)
  5. Eidgenossische Technische Hochschule (ETH) Zurich, Zurich (Switzerland)
Publication Date:
OSTI Identifier:
1343611
Grant/Contract Number:
AC02-76SF00515; AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 91; Journal Issue: 18; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Research Org:
Kansas State Univ., Manhattan, KS (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY