B. Toudic

Temperature-pressure phase diagram of an aperiodic host guest compound

This letter reports on the structural instabilities of an aperiodic composite crystal under pressure. The (P, T) phase diagram up to 0.55u2009GPa of nonadecane-urea is reported showing various symmetry breakings in crystallographic superspaces, towards three different orthorhombic phases. These structural phase transitions are characterized by a change in the intermodulation and are described by increasing the rank of the crystallographic superspaces.

Local Properties in Disordered Mixed M1-xPx Monomer Polymer Crystal : A D-NMR Study

Abstract The influence of the polymerization on the structural phase transition in a mixed monomer-polymer pTS-D system is studied by D-NMR. Results are compared with previous neutron and Raman scattering results.

Experimental Study of the Liquid-Glass Transition in an Inorganic Polymer Li 0.5 Na 0.5 PO 3

New experimental results obtained with various techniques on a less-studied glass-forming system are presented. At low frequency, a secondary β slow -process, decoupled from the viscous flow, is observed by 3 1 P NMR. Raman scattering spectra and coherent neutron scattering spectra has been obtained in wide frequency and temperature ranges showing the same qualitative features for the Boson peak while the quasielastic contribution seems to differ markedly.

Phase Transitions in Aperiodic Composite Crystals

Aperiodic alkane/urea inclusion compounds (UIC) are prototype composites which exhibit complex sequences of phases that can clearly be described in the (3+d) dimension crystallographic superspace. By simply changing the length of the guest alkane molecules (C n H2n+2) which pile up in the channels of the host urea honeycomb-like framework, it is, for instance, possible to have phase-ordering phase transition from 3 to (3+1) dimension in the case of n-heptane/urea (n=7), or as in the case of n-hexadecane/urea (n=16) or n-nonadecane/urea (n=19), a generalization to higher dimensions of the phase transitions found in modulated structures. Such results are successfully obtained with the help of high resolution diffraction methods.

35 Cl NQR and 2 H NMR analysis of the critical dynamics by approaching from above the normal-incommensurate phase transition of Bis-(4-chlorophenyl)-sulfone (BCPS)

Abstract The inverse of the NQR or NMR spin lattice relaxation time of BCPS exhibits a Landau like critical behaviour on approaching the Normal/Incommensurate phase transition from above. This critical behaviour is interpreted as the contribution from the central peak observed in neutron experiments within the framework of the model of a coupling of the soft mode to pure relaxation modes. This result would be consistent with a central peak of dynamical nature.

Fast dynamics of Na0.5Li0.5PO3 observed by coherent neutron scattering

Abstract Experimental results obtained by coherent neutron scattering with the time of flight spectrometer MIBEMOL on the less-fragile glass-forming liquid Na0.5Li0.5PO3 are presented. A qualitative discussion of the susceptibility spectra within the framework of the simplest version of the mode-coupling theory locates a possible crossover temperature Tc near 620 K (∼1.2Tg) close to the temperature of the decoupling phenomena of the relaxation time scales observed by 31P NMR.

Structural and dynamical aspects of the incommensurate molecular system Bis(4-chlorophenyl) sulfone

Abstract Bis(4-chlorophenyl)sulfone is a molecular compound whose structure results from the Van der Waals forces and dipolar moment interactions. The region of diffuse scattering in the range 300 K to the transition temperature TI = 150 K and the location of the incommensurate satellites from TI to 0 K, are very weakly temperature dependent demonstrating the existence of some intrinsic structural character. Neutron scattering results combined with light scattering, 35Cl NQR and X-ray analysis reveal peculiar structural and dynamical features in the compound.