Bertrand Toudic

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We describe a novel type of ordering phenomenon associated with the incommensurate occupational modulation of bistable molecular magnetic state in a spin-crossover material. This unusual type of aperiodicity resulting from the ordering of multistable electronic states opens new possibilities for addressing such materials by light. Here we show that light(More)
Numerous crystalline materials, including those of bioorganic origin, comprise incommensurate sublattices whose mutual arrangement is described in a superspace framework exceeding three dimensions. We report direct observation by neutron diffraction of superspace symmetry breaking in a solid-solid phase transition of an incommensurate host-guest system: the(More)
This Letter reports on the first observation of a commensurate lock-in inside an aperiodic composite. This result is obtained by neutron diffraction, under hydrostatic pressure, in the prototype self-assembled crystal of hexadecane urea. A selective compressibility of the sublattices is a required condition together with the existence of a lock-in energy(More)
This Letter reports on the structural analysis of a self-assembly material, the prototype host-guest urea-alkane nanoporous crystal. Different spectroscopic techniques, under hydrostatic pressure, reveal a totally unexpected ordered phase where ordering does not require any apparent deformation of the host. This fundamental observation raises the question(More)
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(More)
We report on striking evidence for a room temperature structural phase instability in p-hexaphenyl, inducing a nonplanar conformation of the molecules. Solid state proton NMR and single crystal x-ray diffraction allow the analysis of the organization, the individual dynamics and the involved symmetry breaking. The analysis of Raman spectra above and below(More)
n-Heptane/urea is an aperiodic inclusion compound in which the ratio of host and guest repeats along the channel axis is very close to unity and is found to have a constant value (0.981) from 280 K to 90 K. Below 280 K, two phase transitions are observed. The first (T(c1) = 145 K) is a ferroelastic phase transition that generates superstructure reflections(More)
High-resolution studies of the host-guest inclusion compound n-hexadecane/urea are reported at atmospheric pressure, using both cold neutrons and x-ray diffraction. This intergrowth crystal presents a misfit parameter, defined by the ratio c(h)/c(g) (c(host)/c(guest)), which is temperature independent and irrational (γ = 0.486 ± 0.002) from 300 to 30 K.(More)