Pierre Gregoire - Academia.edu (original) (raw)
Papers by Pierre Gregoire
Journal of Experimental and Theoretical Physics Letters, 1996
We present evidence for a thermodynamically stable incommensurate elongated-triangle (ELT) phase ... more We present evidence for a thermodynamically stable incommensurate elongated-triangle (ELT) phase in quartz, observed by transmission electron microscopy at the α-β structural transition. The phase sequence on cooling is: incommensurate equilateral-triangle (EQT) phase (ferroelectric)—incommensurate ELT (ferroelectric and ferroelastic)— uniform α phase. The ELT blocks could be responsible for the large light scattering in the vicinity of the α-gb transition.
Journal of Physics C: Solid State Physics, 1984
ABSTRACT
Techniques De L Ingenieur Mesures Et Controle, 1993
La meteorologie s'interesse principalement a l'etat physique et thermodynamique de l'... more La meteorologie s'interesse principalement a l'etat physique et thermodynamique de l'atmosphere. Les modeles de prevision numerique, actuellement a l'origine des previsions courte et moyenne echeance (1 a 6 jours), modelisent l'atmosphere par un ensemble d'equations thermodynamiques et d'equations de la mecanique des fluides. Les mesures de base necessaires aux modeles numeriques sont essentiellement le vent, la pression, la temperature et l'humidite, au sol mais surtout en altitude. Pour des besoins de la prevision locale, de la climatologie et du suivi en temps reel du temps, pour les utilisateurs professionnels de plus en plus nombreux (agriculture, aviation, transport), des mesures additionnelles sont tres souvent effectuees. Le present texte tente de couvrir l'ensemble des mesures couramment effectuees en meteorologie. L'analyse chimique de l'atmosphere n'est pas, en France, de la responsabilite de la meteorologie et n'est donc pas traitee ici.
Informations Chimie, 1991
La dissolution d'un compose hydrophobe dans une solution aqueuse passe par la mise au point d... more La dissolution d'un compose hydrophobe dans une solution aqueuse passe par la mise au point d'un melange ternaire de produits formant une phase homogene a la fois hydrophile et hydrophobe
Canadian Art Therapy Association Journal, 1996
physica status solidi (a), 2014
ABSTRACT In2S3(1–x)O3x is known from preceding studies to have a bandgap varying continuously as ... more ABSTRACT In2S3(1–x)O3x is known from preceding studies to have a bandgap varying continuously as a function of x, which is the reason why this solid solution is potentially interesting in the field of photovoltaics. In this work, we present results on oxidation of In2S3 by heating in air atmosphere to obtain the desired material. The oxidation is accompanied by a mass loss due to the substitution of S by O atoms that is studied by means of thermogravimetric analysis. It appears that the temperature region in which the oxidation occurs is strongly dependent on the microstructure of deposited films. As-grown films deposited by chemical bath deposition are subjected to nano-oxidation occurring at lower temperature than oxidation of materials that are characterized by a better crystallinity and larger crystallite size. X-ray diffraction and scanning electron microscopy (including energy dispersive X-ray spectroscopy (EDX)) were used to get information on the compounds and the microstructure of films. The main conclusion of the paper opens the perspective of practical applications for producing layers for solar cells.
Solid State Communications, 1991
ABSTRACT The crystalline compound (TMP)2CuBr4, where TMP is the tetramethylphosphonium P(CH3)4, i... more ABSTRACT The crystalline compound (TMP)2CuBr4, where TMP is the tetramethylphosphonium P(CH3)4, is a new member of the well known family A2BX4 which exhibits many examples with structural instabilities, including incommensurate phases. We present results obtained by X-ray diffraction and differential scanning calorimetry on the sequence of phases which occur in this material. The usual parent phase for this family, of symmetry D162h(Pnma, exists above T1 ≌ 135 °C, and three other phases are observed at lower temperatures:P21/n11 (k=0) ⇒ P121/c1 (k=c*/2) ⇒ inc ⇒ Pnma (k=0, Z=4) The incommensurate phase which exists over a very small temperature range, seems to appear in the vicinity of the tricritical point, as discussed at the light of the phenomenological theory.
physica status solidi (a), 1985
Phase Transitions, 1992
The time evolution of the incommensurate to commensurate transition is presented for the solid so... more The time evolution of the incommensurate to commensurate transition is presented for the solid solution (NH4)2(BeF4)0.92(SO4)0.08. After annealing of the sample in the paraelectric phase, the temperature is rapidly decreased and then stabilized in the incommensurate phase. From this time the diffraction profile of the satellite is repeatedly measured for more than 2200 min. The incommensurate phase progressively disappears in
Zeitschrift für Kristallographie - Crystalline Materials, 1995
Hemihydrate / Solid state hydration Abstract. [(C2H5)4N]2CuCl4 crystallizes in the tetragonal sys... more Hemihydrate / Solid state hydration Abstract. [(C2H5)4N]2CuCl4 crystallizes in the tetragonal system (P42/nmc, a = 8.98(3) Â; c = 15.08(3) Â; Z = 2; R = 0.057, 442 hkl observed, 53 variables). The two (C2H5)4N+ and CuCl42~i ons are disordered about intersecting mirror planes. CuCl42~i on has distorted tetrahedral symmetry with elongation along the tetragonal axis. In moist atmosphere, the compound is transformed, by hydration at solid state, into the hemihydrate: [(C2H5)4N]2CuCl4 • 0.5 H20 with tetragonal symmetry. The new 4 axis of the hydrated crystal is perpendicular to the 4 axis of the anhydrous crystal.
Journal of Polymer Science Part B: Polymer Physics, 1989
The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers ne... more The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers near the ferroelectric-to-paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 molS trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 molS TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intermediate supplementary phase. Both hypotheses are d i s c u s r e d .
Journal of Physics: Condensed Matter, 1994
ABSTRACT A theoretical interpretation of the transition sequences in the (P(CH3)4)2 (CuCl4)1-x(Cu... more ABSTRACT A theoretical interpretation of the transition sequences in the (P(CH3)4)2 (CuCl4)1-x(CuBr4)x solid solution is proposed. Each pure compound (P(CH3)4)2CuCl4 and (P(CH3)4)2CuBr4 presents its own transition sequence which contains an incommensurate phase and different locked phases. In the solid solution with x=0.12, phases characteristic of the two pure compounds are observed in the sequence. The interpretation of this phase diagram is based on a coupling of the two order parameters, each of them corresponding to their own phonon branch. This coupling results in a re-entrant symmetry for one of the two order parameters, in agreement with experimental data.
Journal of Organometallic Chemistry, 1995
... Authors: Ohnet M.-N.; Spasojevic-de Bire A.; Dao NQ 1 ; Schweiss P.; Kiat J.-M.; Gregoire P.;... more ... Authors: Ohnet M.-N.; Spasojevic-de Bire A.; Dao NQ 1 ; Schweiss P.; Kiat J.-M.; Gregoire P.; Fischer H.; Reindl D. ... Affiliations: 1: Laboratoire de Physico-Chimie Moleculaire et Minerale PCM, ERS 0070 du CNRS, Ecole Centrale Paris, F-92295 Chatenay-Malabry Cedex, France. ...
The Journal of Chemical Physics, 2002
ABSTRACT The heat capacities of the glassy and liquid states of three lithium chloride aqueous so... more ABSTRACT The heat capacities of the glassy and liquid states of three lithium chloride aqueous solutions (LiCl⋅4H2O,LiCl⋅6H2O,LiCl⋅7.5H2O) were measured with an adiabatic calorimeter in the temperature range 5–340 K; the crystalline state was also measured for LiCl⋅4H2O. For all of the glassy samples, a large non-Debye excess heat capacity appeared below 30 K. The neutron scattering spectra of glassy LiCl⋅4H2O and LiCl⋅6H2O were measured with two spectrometers operating with different energy windows (E<20 meV and E<100 meV). A boson peak, corresponding to the excess heat capacity, appeared at around 4 meV in the S(Q,E) spectra of both glassy samples. From the analysis combining the heat capacity and neutron scattering data, the excess density of states due to the boson peak (compared with hexagonal ice) was found to be 0.10 degree of freedom per water molecule for both glassy samples. A librational peak of water molecules appeared at around 60 meV in glassy samples. This energy is about 10 meV lower than that of hexagonal and amorphous ices, indicating that the hydrogen bonds connecting water molecules are broken due to the strong coordination of water molecules to lithium ions. © 2002 American Institute of Physics.
International Journal of Theoretical and Applied Finance, 2008
We set up a model to study the voluntary disclosure of information by insiders of publicly traded... more We set up a model to study the voluntary disclosure of information by insiders of publicly traded companies. We consider a trading framework as in [14] with many assets and one insider per asset. There is one discretionary liquidity trader who can allocate his trades across the different assets and many noise traders who trade with equal intensity in all assets. Before trade begins, insiders can disclose information in order to attract the discretionary liquidity trades. We show that if the level of noise trading is above a certain threshold, then there is an equilibrium where all insiders do not disclose any information. Below this threshold, equilibria are such that some information is always revealed by insiders. We also find that the greater the number of assets, the smaller the intensity of noise trading must be in order to induce insiders to disclose some information, and we find that insiders reveal all their information when the intensity of noise trading approaches zero.
Ferroelectrics Letters Section, 1990
ABSTRACT
Ferroelectrics, 1993
ABSTRACT We present the transition sequence in {P(CH3)4)2(CuCl4)0.88(CuBr4)0.12. This compound di... more ABSTRACT We present the transition sequence in {P(CH3)4)2(CuCl4)0.88(CuBr4)0.12. This compound displays a rich sequence of phases. At high temperature an incommensurate phase exists, characterized by a modulation in the c direction. At low temperature the crystal is modulated along the a direction. In the intermediate temperature range doubly modulated phases result from the competition of the two pure salts order parameters.
Journal of Experimental and Theoretical Physics Letters, 1996
We present evidence for a thermodynamically stable incommensurate elongated-triangle (ELT) phase ... more We present evidence for a thermodynamically stable incommensurate elongated-triangle (ELT) phase in quartz, observed by transmission electron microscopy at the α-β structural transition. The phase sequence on cooling is: incommensurate equilateral-triangle (EQT) phase (ferroelectric)—incommensurate ELT (ferroelectric and ferroelastic)— uniform α phase. The ELT blocks could be responsible for the large light scattering in the vicinity of the α-gb transition.
Journal of Physics C: Solid State Physics, 1984
ABSTRACT
Techniques De L Ingenieur Mesures Et Controle, 1993
La meteorologie s'interesse principalement a l'etat physique et thermodynamique de l'... more La meteorologie s'interesse principalement a l'etat physique et thermodynamique de l'atmosphere. Les modeles de prevision numerique, actuellement a l'origine des previsions courte et moyenne echeance (1 a 6 jours), modelisent l'atmosphere par un ensemble d'equations thermodynamiques et d'equations de la mecanique des fluides. Les mesures de base necessaires aux modeles numeriques sont essentiellement le vent, la pression, la temperature et l'humidite, au sol mais surtout en altitude. Pour des besoins de la prevision locale, de la climatologie et du suivi en temps reel du temps, pour les utilisateurs professionnels de plus en plus nombreux (agriculture, aviation, transport), des mesures additionnelles sont tres souvent effectuees. Le present texte tente de couvrir l'ensemble des mesures couramment effectuees en meteorologie. L'analyse chimique de l'atmosphere n'est pas, en France, de la responsabilite de la meteorologie et n'est donc pas traitee ici.
Informations Chimie, 1991
La dissolution d'un compose hydrophobe dans une solution aqueuse passe par la mise au point d... more La dissolution d'un compose hydrophobe dans une solution aqueuse passe par la mise au point d'un melange ternaire de produits formant une phase homogene a la fois hydrophile et hydrophobe
Canadian Art Therapy Association Journal, 1996
physica status solidi (a), 2014
ABSTRACT In2S3(1–x)O3x is known from preceding studies to have a bandgap varying continuously as ... more ABSTRACT In2S3(1–x)O3x is known from preceding studies to have a bandgap varying continuously as a function of x, which is the reason why this solid solution is potentially interesting in the field of photovoltaics. In this work, we present results on oxidation of In2S3 by heating in air atmosphere to obtain the desired material. The oxidation is accompanied by a mass loss due to the substitution of S by O atoms that is studied by means of thermogravimetric analysis. It appears that the temperature region in which the oxidation occurs is strongly dependent on the microstructure of deposited films. As-grown films deposited by chemical bath deposition are subjected to nano-oxidation occurring at lower temperature than oxidation of materials that are characterized by a better crystallinity and larger crystallite size. X-ray diffraction and scanning electron microscopy (including energy dispersive X-ray spectroscopy (EDX)) were used to get information on the compounds and the microstructure of films. The main conclusion of the paper opens the perspective of practical applications for producing layers for solar cells.
Solid State Communications, 1991
ABSTRACT The crystalline compound (TMP)2CuBr4, where TMP is the tetramethylphosphonium P(CH3)4, i... more ABSTRACT The crystalline compound (TMP)2CuBr4, where TMP is the tetramethylphosphonium P(CH3)4, is a new member of the well known family A2BX4 which exhibits many examples with structural instabilities, including incommensurate phases. We present results obtained by X-ray diffraction and differential scanning calorimetry on the sequence of phases which occur in this material. The usual parent phase for this family, of symmetry D162h(Pnma, exists above T1 ≌ 135 °C, and three other phases are observed at lower temperatures:P21/n11 (k=0) ⇒ P121/c1 (k=c*/2) ⇒ inc ⇒ Pnma (k=0, Z=4) The incommensurate phase which exists over a very small temperature range, seems to appear in the vicinity of the tricritical point, as discussed at the light of the phenomenological theory.
physica status solidi (a), 1985
Phase Transitions, 1992
The time evolution of the incommensurate to commensurate transition is presented for the solid so... more The time evolution of the incommensurate to commensurate transition is presented for the solid solution (NH4)2(BeF4)0.92(SO4)0.08. After annealing of the sample in the paraelectric phase, the temperature is rapidly decreased and then stabilized in the incommensurate phase. From this time the diffraction profile of the satellite is repeatedly measured for more than 2200 min. The incommensurate phase progressively disappears in
Zeitschrift für Kristallographie - Crystalline Materials, 1995
Hemihydrate / Solid state hydration Abstract. [(C2H5)4N]2CuCl4 crystallizes in the tetragonal sys... more Hemihydrate / Solid state hydration Abstract. [(C2H5)4N]2CuCl4 crystallizes in the tetragonal system (P42/nmc, a = 8.98(3) Â; c = 15.08(3) Â; Z = 2; R = 0.057, 442 hkl observed, 53 variables). The two (C2H5)4N+ and CuCl42~i ons are disordered about intersecting mirror planes. CuCl42~i on has distorted tetrahedral symmetry with elongation along the tetragonal axis. In moist atmosphere, the compound is transformed, by hydration at solid state, into the hemihydrate: [(C2H5)4N]2CuCl4 • 0.5 H20 with tetragonal symmetry. The new 4 axis of the hydrated crystal is perpendicular to the 4 axis of the anhydrous crystal.
Journal of Polymer Science Part B: Polymer Physics, 1989
The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers ne... more The thermal and dielectric behaviors of poly(vinylidene fluoride-trifluoroethylene) copolymers near the ferroelectric-to-paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 molS trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 molS TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intermediate supplementary phase. Both hypotheses are d i s c u s r e d .
Journal of Physics: Condensed Matter, 1994
ABSTRACT A theoretical interpretation of the transition sequences in the (P(CH3)4)2 (CuCl4)1-x(Cu... more ABSTRACT A theoretical interpretation of the transition sequences in the (P(CH3)4)2 (CuCl4)1-x(CuBr4)x solid solution is proposed. Each pure compound (P(CH3)4)2CuCl4 and (P(CH3)4)2CuBr4 presents its own transition sequence which contains an incommensurate phase and different locked phases. In the solid solution with x=0.12, phases characteristic of the two pure compounds are observed in the sequence. The interpretation of this phase diagram is based on a coupling of the two order parameters, each of them corresponding to their own phonon branch. This coupling results in a re-entrant symmetry for one of the two order parameters, in agreement with experimental data.
Journal of Organometallic Chemistry, 1995
... Authors: Ohnet M.-N.; Spasojevic-de Bire A.; Dao NQ 1 ; Schweiss P.; Kiat J.-M.; Gregoire P.;... more ... Authors: Ohnet M.-N.; Spasojevic-de Bire A.; Dao NQ 1 ; Schweiss P.; Kiat J.-M.; Gregoire P.; Fischer H.; Reindl D. ... Affiliations: 1: Laboratoire de Physico-Chimie Moleculaire et Minerale PCM, ERS 0070 du CNRS, Ecole Centrale Paris, F-92295 Chatenay-Malabry Cedex, France. ...
The Journal of Chemical Physics, 2002
ABSTRACT The heat capacities of the glassy and liquid states of three lithium chloride aqueous so... more ABSTRACT The heat capacities of the glassy and liquid states of three lithium chloride aqueous solutions (LiCl⋅4H2O,LiCl⋅6H2O,LiCl⋅7.5H2O) were measured with an adiabatic calorimeter in the temperature range 5–340 K; the crystalline state was also measured for LiCl⋅4H2O. For all of the glassy samples, a large non-Debye excess heat capacity appeared below 30 K. The neutron scattering spectra of glassy LiCl⋅4H2O and LiCl⋅6H2O were measured with two spectrometers operating with different energy windows (E<20 meV and E<100 meV). A boson peak, corresponding to the excess heat capacity, appeared at around 4 meV in the S(Q,E) spectra of both glassy samples. From the analysis combining the heat capacity and neutron scattering data, the excess density of states due to the boson peak (compared with hexagonal ice) was found to be 0.10 degree of freedom per water molecule for both glassy samples. A librational peak of water molecules appeared at around 60 meV in glassy samples. This energy is about 10 meV lower than that of hexagonal and amorphous ices, indicating that the hydrogen bonds connecting water molecules are broken due to the strong coordination of water molecules to lithium ions. © 2002 American Institute of Physics.
International Journal of Theoretical and Applied Finance, 2008
We set up a model to study the voluntary disclosure of information by insiders of publicly traded... more We set up a model to study the voluntary disclosure of information by insiders of publicly traded companies. We consider a trading framework as in [14] with many assets and one insider per asset. There is one discretionary liquidity trader who can allocate his trades across the different assets and many noise traders who trade with equal intensity in all assets. Before trade begins, insiders can disclose information in order to attract the discretionary liquidity trades. We show that if the level of noise trading is above a certain threshold, then there is an equilibrium where all insiders do not disclose any information. Below this threshold, equilibria are such that some information is always revealed by insiders. We also find that the greater the number of assets, the smaller the intensity of noise trading must be in order to induce insiders to disclose some information, and we find that insiders reveal all their information when the intensity of noise trading approaches zero.
Ferroelectrics Letters Section, 1990
ABSTRACT
Ferroelectrics, 1993
ABSTRACT We present the transition sequence in {P(CH3)4)2(CuCl4)0.88(CuBr4)0.12. This compound di... more ABSTRACT We present the transition sequence in {P(CH3)4)2(CuCl4)0.88(CuBr4)0.12. This compound displays a rich sequence of phases. At high temperature an incommensurate phase exists, characterized by a modulation in the c direction. At low temperature the crystal is modulated along the a direction. In the intermediate temperature range doubly modulated phases result from the competition of the two pure salts order parameters.