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Long-range modulation in a five-dimensional crystallographic superspace

Abstract : The intergrowth crystal of -tetracosane/urea presents a misfit parameter, defined by the ratio = / (/), that is very close to a commensurate value ( ≅ 1/3). High-resolution diffraction studies presented here reveal an aperiodic misfit parameter of = 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 622(00). At = 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 222(00)(10) with a modulation vector + = + · , in which the supplementary misfit parameter is = 0.025(1) in host reciprocal units. This corresponds to the appearance of a modulation of very long period (about 440 ± 16 Å). At = 163.0(5) K, a 5D to 5D phase transition leads to the crystallographic superspace group 222(00)(00) with a very similar value of . This phase transition reveals a significant hysteresis effect.
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Submitted on : Friday, June 26, 2015 - 10:12:14 AM
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Laurent Guérin, Céline Mariette, Philippe Rabiller, Michael Huard, Sylvain Ravy, et al.. Long-range modulation in a five-dimensional crystallographic superspace. Physical Review B: Condensed Matter and Materials Physics, American Physical Society, 2015, 91 (18), pp.184101. ⟨10.1103/PhysRevB.91.184101⟩. ⟨hal-01164047v2⟩

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