title: The creation of modulated monoclinic aperiodic composites inn-alkane/urea compounds.
abstract: n-Dodecane/urea is a member of the prototype series ofn-alkane/urea inclusion compounds. At room temperature, it presents a quasi-one dimensional liquid-like state for the confined guest molecules within the rigid, hexagonal framework of the urea host. At lower temperatures, we report the existence of two other phases. Below Tc=248 K there appears a phase with rank four superspace group P6122(00γ), the one typically observed at room temperature inn-alkane/urea compounds with longer guest molecules. A misfit parameter, defined by the ratio γ=ch/cg(chost/cguest), is found to be 0.632±0.005. Below Tc1=123 K, a monoclinic modulated phase is created with a constant shift alongcof the guest molecules in adjacent channels. The maximal monoclinic space group for this structure is P1211(α0γ). Analogies and differences withn-heptane/urea, which also presents a monoclinic, modulated low-temperature phase, are discussed.
authors.affiliation: Institut de Physique de Rennes, UMR UR1-CNRS 6251, Université de Rennes 1, 35042 Rennes, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Mariette
authors.affiliation: Institut de Physique de Rennes, UMR UR1-CNRS 6251, Université de Rennes 1, 35042 Rennes, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Guérin
authors.affiliation: Institut de Physique de Rennes, UMR UR1-CNRS 6251, Université de Rennes 1, 35042 Rennes, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Rabiller
authors.affiliation: Argonne Photon Source (APS), ANL, 9700 South Cass Ave., Argonne, IL 60439, USA.
authors.forename: Yu-Sheng
authors.initials: YS
authors.lastname: Chen
authors.affiliation: European Synchrotron Radiation Facility (ESRF), 71, Avenue des Martyrs, Grenoble, France.
authors.forename: Alexei
authors.initials: A
authors.lastname: Bosak
authors.affiliation: European Synchrotron Radiation Facility (ESRF), 71, Avenue des Martyrs, Grenoble, France.
authors.forename: Alexander
authors.initials: A
authors.lastname: Popov
authors.affiliation: Department of Chemistry, 213 CBC Building, Kansas State University, Manhattan, Kansas 66506-0401, USA.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Hollingsworth
authors.affiliation: C.N.R.S., Directeur de Recherche, Department of Physics, University of Rennes 1, Campus de Beaulieu, Rennes, France.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Toudic
keywords: alkane/urea crystals; aperiodic crystals; crystallographic superspace; diffraction; phase transitions