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Papers by Michel Couzi

A variable-temperature hydrostatic high-pressure cell for Raman scattering experiments is present... more A variable-temperature hydrostatic high-pressure cell for Raman scattering experiments is presented; it can be commonly used for pressures up to about 6 kbars, in the temperature range between 340 and 80 K. Examples of applications are given, concerning conformational equilibriums in liquid tridecane on the one hand, and structural phase transitions in crystalline (CH3)4NMnCI3(TMMC) and (CH3)4NCdCI3 (TMCC), on the other hand.

Physics and Chemistry of Glasses

The very attractive ionic conductivity of both Li 2 S-B 2 S 3 and Li 2 S-As 2 S 3 based glasses l... more The very attractive ionic conductivity of both Li 2 S-B 2 S 3 and Li 2 S-As 2 S 3 based glasses leads to the study of a possible mixed former effect. The glassy domain obtained is quite small and, due to the presence of one or two T g , two regions, homogeneous and inhomogeneous, have been found. The expected increase of ionic conductivity characteristic of the mixed former effect is not present. Characterisation of these glasses by infrared and Raman spectroscopy shows, in spite of their appearance, that these amorphous materials are probably composed of two separated glasses even in the homogeneous region.

Journal of Physics C Solid State Physics

The structural phase transitions occurring in the chain compounds (CH,),NMnCI, (TMMC) and (CH3)4N... more The structural phase transitions occurring in the chain compounds (CH,),NMnCI, (TMMC) and (CH3)4NCdC13 (TMCC) are studied through x-ray diffraction measurements. In both compounds, the existence of a new high-temperature orientationally disordered phase is established (phase 1') with space group PB,/mmc and Z = 2 (parent phase). The roomtemperature phase I of TMMC and TMCC (space group P63/m and Z = 2) derives from I' by a rotation of the octahedra chains about the c axis; orientational disorder of the (CH3)4N' group (TMA) in phase I is described by a complex Frenkel model involving at least five different orientations of the TMA. Phase 11 Of TMMC (space group PZ,/b with Z = 4) is derived from phase I by anti-phase translational displacements of the octahedra chains along the c axis; an important amount of residual disorder of the TMA is observed just below the I U I1 transition temperature. In TMCC, the space group R , / m ( Z = 2) of phase I11 is confirmed, whereas phase IV exhibits a complex structure (space group R , / b with Z = 12) corresponding to a trebling of the lattice constant along c and a doubling along b. X-ray diffuse scattering experiments on TMMC and TMCC are also reported. In phase I, the diffuse scattering patterns are interpreted in terms of 'linear' translational disorder of the octahedra chains along the c axis: In phase I1 of TMMC, a residual translational disorder of the chains is evidenced, just below the I * I1 transition temperature. These results show that orientational disorder of the TMA group is coupled to translational disorder of the octahedra chain sublattice.

Journal de Physique I, 1991

Berichte der Bunsengesellschaft für physikalische Chemie, 1983

Journal of Physics C: Solid State Physics, 1983

A Raman scattering study of the non-ferroic and of the improper ferroeleastic structural phase tr... more A Raman scattering study of the non-ferroic and of the improper ferroeleastic structural phase transitions (SFT) in the perovskite-type layer compound RbAIF4 is reported. It is shown that the SPT occurring at T,I = 551 K (Dah Dih) and at Tc2 = 282 K (D& e D;:) are related to displacive mechanisms owing to the occurrence of one and two soft phonons below Tcl and Tc2 respectively. The results are consistent with a first-order character for the SFT at Tcl and a second-order character for that at TQ. Moreover, in the tetragonal Dah and Dlh phases, the Raman spectra exhibit a number of features which cannot be explained by the selection rules at q = 0. In particular, one of these additional lines exhibits a soft-mode behaviour above the Td transition, while the condensing phonon is a zone-boundary mode. Such features are imputed to the loss of translational symmetry caused by the existence of intrinsic structural disorder.

Optics Communications, 2008

Using, a time resolved optical heterodyne Kerr effect experiment along with a Raman light diffusi... more Using, a time resolved optical heterodyne Kerr effect experiment along with a Raman light diffusion experiment, we have measured the nuclear (non-instantaneous) and electronic (instantaneous) contributions to the nonlinear index of refraction in tellurite niobiumdoped and silicate lead-doped glasses. The experimental set-up and the procedure used to measure the nuclear and electronic contribution are detailed. Our experimental results clearly indicate that the ratio between the instantaneous and the non-instantaneous contribution remain constant while the doping concentration or the temperature of the sample vary. These ratios are 5and5 and 5and10 in tellurite niobium-doped and silicate lead glasses, respectively.

Journal of the Optical Society of America B, 1998

The electronic and nuclear contributions to the third-order nonlinearity of glasses are separated... more The electronic and nuclear contributions to the third-order nonlinearity of glasses are separated by use of 100-fs pulses in a time-resolved heterodyne optical Kerr effect technique. A direct estimate of the relative strengths of electronic and nuclear contributions was made by the comparison between the nuclear contribution deduced from the Raman spectra with the Kerr signal. The ratio between the electronic and nuclear response functions was ϳ5/1 in a tellurium oxide glass sample. The time evolution of the nuclear contribution is in good agreement with results deduced from the Raman spectra.

Journal of Physics and Chemistry of Solids, 1975

AU the predicted Baman active translatory vibrations of wurtzite ammonium fluoride (space group C... more AU the predicted Baman active translatory vibrations of wurtzite ammonium fluoride (space group C&) are observed and assigned on the basis of their polarization selections obtained with single crystals. The f~d~ent~ ~0~~

Journal of Physics and Chemistry of Solids, 1994

In the series of molecular composites of perovskite-type layer structures NH,--(CH,),-NH, MCI,, t... more In the series of molecular composites of perovskite-type layer structures NH,--(CH,),-NH, MCI,, the derivative with n = 4 and M = Cd appears as a particular case, compared to other homologous compounds (M = Mn). The distance between two successive perovskite layers, which is dependent on the molecular chain length, appears very short in the crystalline initial form. The polymorphism has been studied by thermal and crystallographic investigations on both powder and single-crystal materials. Five crystalline forms V, IV, III, II and I have been evidenced. The irreversibility or reversibility of the different phase transitions has been established. Structure determinations of the "limit" phases V (initial room-temperature form), III (high-temperature form) and I (new room-temperature form) allow us to correlate the different phase transitions of this complex to the conformational evolutions of the organic part W-k-V-4)4--NH31 *+ The results show that a temperature increase on form V leads to an . irreversible transformation from gauche to all-trans conformation in the organic chain which keeps the definitive conformation in further phase transitions. Orientational disorder of the chain appears in the high-temperature phase and its evolution with decreasing temperature has been analysed from entropy change measurements.

Journal of Molecular Structure, 1970

The Journal of Chemical Physics, 1973

The Journal of Chemical Physics, 1982

Diamond and Related Materials, 1993

Chemical Physics Letters, 1970

Vibration-rotation fine structure is observed in the spectra of solutiors of HF. DF 2nd BCL in li... more Vibration-rotation fine structure is observed in the spectra of solutiors of HF. DF 2nd BCL in liquid SF6. These spectral features are interpreted in terms of rotational motions of the solutes iE solution.

Chemical Physics Letters, 2013

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.

The Journal of Physical Chemistry C, 2008

We propose and describe combined multipolar vibrational decompositions of IR, polarized Raman and... more We propose and describe combined multipolar vibrational decompositions of IR, polarized Raman and hyper-Raman spectra as a powerful method to study and interpret vibrational spectra in isotropic materials. We have applied this new method to the molecular liquid ...

The Journal of Physical Chemistry B, 2004

In carbon nanotubes and nanofilaments, the surface properties play a fundamental role for any use... more In carbon nanotubes and nanofilaments, the surface properties play a fundamental role for any use or application. It is therefore necessary to know and to control their surface characteristics, which are dependent on the fabrication process and surface treatments. In this work, two selected series of multiwalled nanotubes on which a thermal treatment and/or a controlled surface oxidation, using nitric acid solutions, have been carried out. The structural changes of the nanotubes due to these treatments have been followed by means of two different approaches: first, a solid-state chemistry approach with the determination of chemical surface properties of the carbon characterized by the active surface area (ASA) concept and, second, a more physical approach with Raman microspectroscopy. With this track, it was possible to quantify the surface/morphology ratio in nanotubes, especially in relation with their wettability and adhesion. Hence, we have established a general relationship between physical and chemical approaches that should be valid for any mesoporous, and even macroporous, carbons.