Robert Papoular - Academia.edu (original) (raw)
Papers by Robert Papoular
Acta Crystallographica Section C Crystal Structure Communications, 1998
Physica B: Condensed Matter, 1997
Abstract It is commonplace to assert that neutrons are a good probe for protons and deuterons in ... more Abstract It is commonplace to assert that neutrons are a good probe for protons and deuterons in solids, all the more so when all the remaining atoms (backbone) are reasonably well known from previous accurate X-ray measurements. When the protons are disordered, however, good is not good enough without a suitable unconventional data analysis. By (i) removing most of the truncation effects, (ii) allowing for the use of prior chemical knowledge, (iii) making use of the experimental error bars and (iv) taking advantage of the negative scattering length of the proton which overrides the huge incoherent cross-section of the latter (at least in the case of single-crystal diffraction), maximum entropy asserts itself as an ideal tool for model-free computer-assisted proton vision that easily supersedes the commonly used Fourier and difference Fourier syntheses. A typical example will be discussed.
Journal of Magnetism and Magnetic Materials, 1981
Neutron diffraction measurements were made on powder samples of Crl-xRux (x = 0.003, 0.015 and 0.... more Neutron diffraction measurements were made on powder samples of Crl-xRux (x = 0.003, 0.015 and 0.050) alloys to establish the types of antiferromagnetic order in this system. The results show that three types of antiferromagnetic order (longitudinal-incommensurate, transverse-incommensurate and commensurate) occur within this concentration range. The N6el temperatures for the three alloys are 380, 480 and 514 K, respectively. Only the commensurate phase develops in the 1.5 and 5.0% samples, while all three occur in the 0.3% one. Thermal expansion (determined from neutron diffraction spectra at various temperatures) as well as low-temperature susceptibility measurements show that the behaviour of the 0.3% alloy differs significantly from that of the other two. Both the susceptibility and thermal expansion present an anomaly at a temperature in agreement with the incommensurate-commensurate phase transition observed by neutron diffraction.
Chemical Physics Letters, 2004
Crystals grown by evaporating C 60 solutions in n-nonane were found to be crystals of the C 60 AE... more Crystals grown by evaporating C 60 solutions in n-nonane were found to be crystals of the C 60 AE 2/3 n-nonane solvate, after they were stored for eight years in the dark at room temperature. The lattice is an I-centered orthorhombic lattice (a = 10.10(1) Å , b = 10.19(1) Å , c = 48.71(5) Å), that forms with a negative excess volume of about À3.1%, and loses its solvent from about 399 K with an enthalpy change of about 49 J per gram of solvate. Thermodynamic and crystallographic data for available C 60-n-alcane solvates are discussed and a van der Waals volume of %603 Å 3 per C 60 isolated molecule is proposed.
Carbon, 2005
At room temperature, the hexagonal C 60. 2(CH 3)CCl 3 solvate (a = 10.13(1) Å , c = 10.84(1) Å), ... more At room temperature, the hexagonal C 60. 2(CH 3)CCl 3 solvate (a = 10.13(1) Å , c = 10.84(1) Å), made of alternating layers of C 60 and solvent molecules, forms with a negative excess volume, and its desolvation enthalpy is virtually the same as the sublimation enthalpy of the pure solvent. Crystallographic and calorimetric studies vs temperature indicate that hexagonal C 60. 2(CH 3)CCl 3 changes at 211.7 K (1.3 kJ mol À1 of solvate) into an intermediate triclinic phase which transforms at 189.7 K (4.1 kJ mol À1 of solvate) into another triclinic phase. A crystallographic analysis in the series of hexagonal C 60. 2 YCCl 3 solvates (Y = H, Cl, Br, CH 3) reveals that: (i) the change in the unit-cell volume values is due to a change in axis c whose value depends on the size of Y, (ii) the molar volume of the solvates depends linearly on the molar volume of the solvents. Ageing studies at room temperature show that C 60. 2(CH 3)CCl 3 loses its solvent molecules within a few days or a few months, depending on storage conditions.
Powder Diffraction, 2019
A straightforward intuitive user-friendly compact graphical interface, PreDICT (Premier DICVOL To... more A straightforward intuitive user-friendly compact graphical interface, PreDICT (Premier DICVOL Tool) has been developed to take full advantage of the new capabilities of the most recent version of the DICVOL14 Indexing Software. The latter, an updated version of DICVOL04, includes optimizations, e.g. for monoclinic and triclinic cases, a detailed review of the input data from the indexing solutions, cell centering tests, as well as the handling of a moderate number of impurity peaks. Among the most salient features of PreDICT, one can mention the ability (1) to use 2θnon-equistepped input 1D X-ray powder diffraction patterns as can be obtained from 2D detectors, (2) to strip laboratory data from itsKα2contribution when present, (3) to generate 2θequistepped output 1D X-ray powder diffraction patterns in both the “.XY” and “.GSA” formats. In addition, PreDICT allows for the following features: (1) full access to the native DICVOL14 input/output ASCII file system is retained, (2) for ...
One of the notable advantages of molecular materials is the ability to precisely tune structure, ... more One of the notable advantages of molecular materials is the ability to precisely tune structure, properties, and function via molecular substitutions. While many studies have demonstrated this principle with classic carboxylate‐based coordination polymers, there are comparatively fewer examples where systematic changes to sulfur‐based coordination polymers have been investigated. Here we present such a study on 1D coordination chains of redox‐activeiron-sulfur clusters linked by methylated 1,4‐benzene‐dithiolates. A series of new iron-sulfur based coordination polymers were synthesized with either 2,5‐dimethyl‐1,4‐benzenedithiol (DMBDT) or 2,3,5,6‐tetramethyl‐1,4‐benzenedithiol. The structures of these compounds have been characterized based on synchrotron Xraypowder diffraction while their chemical and physical properties have been characterized by techniques including X‐ray photoelectron spectroscopy, cyclic voltammetry and UV–visible spectroscopy. Methylation results in the gener...
Comptes Rendus. Chimie, 2021
Whitlockite structures in kidney stones indicate infectious origin: a scanning electron microscop... more Whitlockite structures in kidney stones indicate infectious origin: a scanning electron microscopy and Synchrotron Radiation investigation
AIP Conference Proceedings, 2002
Revue de Physique Appliquée, 1984
Physical Review B, 1988
Neutron depolarization measurements have been carried out in order to investigate superconductivi... more Neutron depolarization measurements have been carried out in order to investigate superconductivity in the YBa2Cu307-, system on both powdered and sintered polycrystalline samples. This technique provides indirect evidence of superconductivity through magnetic-flux trapping in low fields as well as vortex-line penetration in higher fields. Powdered and sintered samples show markedly different behavior, probably connected to their granular nature: a sintered sample traps magnetic flux by developing shielding currents when a low magnetic field ((100 Oe) is removed after being applied below the superconducting temperature T"whereas a powder does not. T, can be well determined (about 90 K) whereas H, &(T) can only be estimated.
Journal de Physique II, 1991
Physical Review B, 1991
The dynamical behavior of sodium nitrite in the vicinity of the paraelectric-incommensurate phase... more The dynamical behavior of sodium nitrite in the vicinity of the paraelectric-incommensurate phase transition has been reinvestigated by means of the high-resolution neutron spin-echo technique, in particular, in the modulated phase. It is shown that the results obtained in the incommensurate phase are consistent with a model featuring two slow relaxation mechanisms corresponding to fluctuations in the amplitude and phase
Astronomy and Astrophysics
ABSTRACT
Physica B: Condensed Matter, 1989
... Physica B 156 157 (1989) 871873 NorthHolland, Amsterdam POLARIZED NEUTRON STUDY OF THE YBa2Cu... more ... Physica B 156 157 (1989) 871873 NorthHolland, Amsterdam POLARIZED NEUTRON STUDY OF THE YBa2Cu307x SYSTEM RJ PAPOULARt and G. COLLIN Z 'Laboratoire Leon Brillouin (CEACNRS), CENSaclay, 91191 GifsurYvette Cedex, France ZLaboratoire de Physique ...
Monthly Notices of the Royal Astronomical Society, 2014
Far-infrared (FIR) data on the optical properties of graphite are presently lacking. An important... more Far-infrared (FIR) data on the optical properties of graphite are presently lacking. An important step towards filling this gap was taken by Kuzmenko et al. who measured, on highly oriented pyrolitic graphite at normal incidence and from 10 to 300 K, the in-plane dielectric functions from 0.3 to 200 μm, and the reflectance between 0.3 and about 300 μm. We show here how, using recent developments of the electron theory of graphene, extended to graphite, it is possible to properly extrapolate the data farther even than 1000 μm, in effect all the way to direct current. The plasma frequency as well as the scattering rate of free electrons are shown to both decrease with T, but level off near 0 K, in agreement with theory. Along the way, we noticed significant discrepancies with the well-known and often used derivation of Philipp at room temperature, and also with previous data on temperature dependence and absorbance of graphitic material samples in different physical forms. Possible reasons for these discrepancies are discussed. Finally, the absorption efficiency of small graphitic spheres is deduced for the spectral range from 0.3 to 10000 μm. This may contribute to the discussion on model dust candidates for recently observed astronomical FIR emissions.
Materials Science Forum, 2004
A recent measurement on the high-pressure phase of Ca(OH)2using high-resolution synchrotron X-ray... more A recent measurement on the high-pressure phase of Ca(OH)2using high-resolution synchrotron X-ray powder diffraction has been carried out on a hydrogenated sample at high-temperature. It complements an earlier time-of-flight neutron measurement carried out in the US on a deuterated sample at low temperature. The two protons are found by Rietveld refinement using a new suitable non-Fourier based strategy, for which GSAS and FullProf yield very similar results. Our X-ray result agrees with the previous neutron study for one proton site only, prompting us to reinvestigate the neutron data. A second new and distinct non Fourier-based strategy coupled with GSAS is used to tackle the latter data and indeed confirms the US results. Whilst the reasons for this X-Ray vs Neutron discrepancy can only be guessed at this stage, the use of the two related proton-finding strategies could be extended beyond our specific study.
Physical Review Letters, 2002
By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously la... more By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously large magnetization density is observed on the in-plane oxygen in Ca1.5Sr0.5RuO4. Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding µRu = 0.346(11) µB, µO1 = 0.076(6) µB and µO2 = 0.009(6) µB. The moment on the oxygen arises from the strong hybridization between the Ru-4d and O-2p orbitals. The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the xy (t2g band) d-orbitals.
Physica Status Solidi (a), 1993
Powder neutron diffraction measurements are made on (CD,ND,),MnCl, (d-MAMC) as a function of both... more Powder neutron diffraction measurements are made on (CD,ND,),MnCl, (d-MAMC) as a function of both pressure ((2 to 25) x 10' Pa) and temperature (1.4 to 300 K). The P, T phase diagram, including a new high pressure (HP) phase, is probably of the same kind as that determined previously by Mokhlisse and Couzi for the cadmium homologue. The H P phase of d-MAMC is triclinic (pseudomonoclinic). Magnetic transitions are also reported at TN % 44 K (P = 2 x 10' Pa), occurring in the monoclinic low temperature (MLT) phase, and TN % 50 K (P = 25 x lo8 Pa) occurring in the H P phase. Des mesures de diffraction des neutrons sont rtaliskes sur des Cchantillons polycristallins de (CD,ND,),MnCI, (d-MAMC) en fonction de la pression ((2 a 25) x 10' Pa) et de la temperature (1.4 a 300 K). Le diagramme de phase P, T faisant apparaitre une phase nouvelle sous haute pression (HP) est probablement de mime type que celui ttabli prkckdemment sur le compost homologue du cadmium par Mokhlisse et Couzi. La phase HP du d-MAMC est triclinique (pseudo-monoclinique). Des transitions de phase magnttiques sont mises en tvidence dans la phase MLT a TN x 44 K (P = 2 x 10' Pa) et dans la phase H P a TN N 50 K (P = 25 x lo8 Pa).
Physica B: Condensed Matter, 1997
ABSTRACT
Acta Crystallographica Section C Crystal Structure Communications, 1998
Physica B: Condensed Matter, 1997
Abstract It is commonplace to assert that neutrons are a good probe for protons and deuterons in ... more Abstract It is commonplace to assert that neutrons are a good probe for protons and deuterons in solids, all the more so when all the remaining atoms (backbone) are reasonably well known from previous accurate X-ray measurements. When the protons are disordered, however, good is not good enough without a suitable unconventional data analysis. By (i) removing most of the truncation effects, (ii) allowing for the use of prior chemical knowledge, (iii) making use of the experimental error bars and (iv) taking advantage of the negative scattering length of the proton which overrides the huge incoherent cross-section of the latter (at least in the case of single-crystal diffraction), maximum entropy asserts itself as an ideal tool for model-free computer-assisted proton vision that easily supersedes the commonly used Fourier and difference Fourier syntheses. A typical example will be discussed.
Journal of Magnetism and Magnetic Materials, 1981
Neutron diffraction measurements were made on powder samples of Crl-xRux (x = 0.003, 0.015 and 0.... more Neutron diffraction measurements were made on powder samples of Crl-xRux (x = 0.003, 0.015 and 0.050) alloys to establish the types of antiferromagnetic order in this system. The results show that three types of antiferromagnetic order (longitudinal-incommensurate, transverse-incommensurate and commensurate) occur within this concentration range. The N6el temperatures for the three alloys are 380, 480 and 514 K, respectively. Only the commensurate phase develops in the 1.5 and 5.0% samples, while all three occur in the 0.3% one. Thermal expansion (determined from neutron diffraction spectra at various temperatures) as well as low-temperature susceptibility measurements show that the behaviour of the 0.3% alloy differs significantly from that of the other two. Both the susceptibility and thermal expansion present an anomaly at a temperature in agreement with the incommensurate-commensurate phase transition observed by neutron diffraction.
Chemical Physics Letters, 2004
Crystals grown by evaporating C 60 solutions in n-nonane were found to be crystals of the C 60 AE... more Crystals grown by evaporating C 60 solutions in n-nonane were found to be crystals of the C 60 AE 2/3 n-nonane solvate, after they were stored for eight years in the dark at room temperature. The lattice is an I-centered orthorhombic lattice (a = 10.10(1) Å , b = 10.19(1) Å , c = 48.71(5) Å), that forms with a negative excess volume of about À3.1%, and loses its solvent from about 399 K with an enthalpy change of about 49 J per gram of solvate. Thermodynamic and crystallographic data for available C 60-n-alcane solvates are discussed and a van der Waals volume of %603 Å 3 per C 60 isolated molecule is proposed.
Carbon, 2005
At room temperature, the hexagonal C 60. 2(CH 3)CCl 3 solvate (a = 10.13(1) Å , c = 10.84(1) Å), ... more At room temperature, the hexagonal C 60. 2(CH 3)CCl 3 solvate (a = 10.13(1) Å , c = 10.84(1) Å), made of alternating layers of C 60 and solvent molecules, forms with a negative excess volume, and its desolvation enthalpy is virtually the same as the sublimation enthalpy of the pure solvent. Crystallographic and calorimetric studies vs temperature indicate that hexagonal C 60. 2(CH 3)CCl 3 changes at 211.7 K (1.3 kJ mol À1 of solvate) into an intermediate triclinic phase which transforms at 189.7 K (4.1 kJ mol À1 of solvate) into another triclinic phase. A crystallographic analysis in the series of hexagonal C 60. 2 YCCl 3 solvates (Y = H, Cl, Br, CH 3) reveals that: (i) the change in the unit-cell volume values is due to a change in axis c whose value depends on the size of Y, (ii) the molar volume of the solvates depends linearly on the molar volume of the solvents. Ageing studies at room temperature show that C 60. 2(CH 3)CCl 3 loses its solvent molecules within a few days or a few months, depending on storage conditions.
Powder Diffraction, 2019
A straightforward intuitive user-friendly compact graphical interface, PreDICT (Premier DICVOL To... more A straightforward intuitive user-friendly compact graphical interface, PreDICT (Premier DICVOL Tool) has been developed to take full advantage of the new capabilities of the most recent version of the DICVOL14 Indexing Software. The latter, an updated version of DICVOL04, includes optimizations, e.g. for monoclinic and triclinic cases, a detailed review of the input data from the indexing solutions, cell centering tests, as well as the handling of a moderate number of impurity peaks. Among the most salient features of PreDICT, one can mention the ability (1) to use 2θnon-equistepped input 1D X-ray powder diffraction patterns as can be obtained from 2D detectors, (2) to strip laboratory data from itsKα2contribution when present, (3) to generate 2θequistepped output 1D X-ray powder diffraction patterns in both the “.XY” and “.GSA” formats. In addition, PreDICT allows for the following features: (1) full access to the native DICVOL14 input/output ASCII file system is retained, (2) for ...
One of the notable advantages of molecular materials is the ability to precisely tune structure, ... more One of the notable advantages of molecular materials is the ability to precisely tune structure, properties, and function via molecular substitutions. While many studies have demonstrated this principle with classic carboxylate‐based coordination polymers, there are comparatively fewer examples where systematic changes to sulfur‐based coordination polymers have been investigated. Here we present such a study on 1D coordination chains of redox‐activeiron-sulfur clusters linked by methylated 1,4‐benzene‐dithiolates. A series of new iron-sulfur based coordination polymers were synthesized with either 2,5‐dimethyl‐1,4‐benzenedithiol (DMBDT) or 2,3,5,6‐tetramethyl‐1,4‐benzenedithiol. The structures of these compounds have been characterized based on synchrotron Xraypowder diffraction while their chemical and physical properties have been characterized by techniques including X‐ray photoelectron spectroscopy, cyclic voltammetry and UV–visible spectroscopy. Methylation results in the gener...
Comptes Rendus. Chimie, 2021
Whitlockite structures in kidney stones indicate infectious origin: a scanning electron microscop... more Whitlockite structures in kidney stones indicate infectious origin: a scanning electron microscopy and Synchrotron Radiation investigation
AIP Conference Proceedings, 2002
Revue de Physique Appliquée, 1984
Physical Review B, 1988
Neutron depolarization measurements have been carried out in order to investigate superconductivi... more Neutron depolarization measurements have been carried out in order to investigate superconductivity in the YBa2Cu307-, system on both powdered and sintered polycrystalline samples. This technique provides indirect evidence of superconductivity through magnetic-flux trapping in low fields as well as vortex-line penetration in higher fields. Powdered and sintered samples show markedly different behavior, probably connected to their granular nature: a sintered sample traps magnetic flux by developing shielding currents when a low magnetic field ((100 Oe) is removed after being applied below the superconducting temperature T"whereas a powder does not. T, can be well determined (about 90 K) whereas H, &(T) can only be estimated.
Journal de Physique II, 1991
Physical Review B, 1991
The dynamical behavior of sodium nitrite in the vicinity of the paraelectric-incommensurate phase... more The dynamical behavior of sodium nitrite in the vicinity of the paraelectric-incommensurate phase transition has been reinvestigated by means of the high-resolution neutron spin-echo technique, in particular, in the modulated phase. It is shown that the results obtained in the incommensurate phase are consistent with a model featuring two slow relaxation mechanisms corresponding to fluctuations in the amplitude and phase
Astronomy and Astrophysics
ABSTRACT
Physica B: Condensed Matter, 1989
... Physica B 156 157 (1989) 871873 NorthHolland, Amsterdam POLARIZED NEUTRON STUDY OF THE YBa2Cu... more ... Physica B 156 157 (1989) 871873 NorthHolland, Amsterdam POLARIZED NEUTRON STUDY OF THE YBa2Cu307x SYSTEM RJ PAPOULARt and G. COLLIN Z 'Laboratoire Leon Brillouin (CEACNRS), CENSaclay, 91191 GifsurYvette Cedex, France ZLaboratoire de Physique ...
Monthly Notices of the Royal Astronomical Society, 2014
Far-infrared (FIR) data on the optical properties of graphite are presently lacking. An important... more Far-infrared (FIR) data on the optical properties of graphite are presently lacking. An important step towards filling this gap was taken by Kuzmenko et al. who measured, on highly oriented pyrolitic graphite at normal incidence and from 10 to 300 K, the in-plane dielectric functions from 0.3 to 200 μm, and the reflectance between 0.3 and about 300 μm. We show here how, using recent developments of the electron theory of graphene, extended to graphite, it is possible to properly extrapolate the data farther even than 1000 μm, in effect all the way to direct current. The plasma frequency as well as the scattering rate of free electrons are shown to both decrease with T, but level off near 0 K, in agreement with theory. Along the way, we noticed significant discrepancies with the well-known and often used derivation of Philipp at room temperature, and also with previous data on temperature dependence and absorbance of graphitic material samples in different physical forms. Possible reasons for these discrepancies are discussed. Finally, the absorption efficiency of small graphitic spheres is deduced for the spectral range from 0.3 to 10000 μm. This may contribute to the discussion on model dust candidates for recently observed astronomical FIR emissions.
Materials Science Forum, 2004
A recent measurement on the high-pressure phase of Ca(OH)2using high-resolution synchrotron X-ray... more A recent measurement on the high-pressure phase of Ca(OH)2using high-resolution synchrotron X-ray powder diffraction has been carried out on a hydrogenated sample at high-temperature. It complements an earlier time-of-flight neutron measurement carried out in the US on a deuterated sample at low temperature. The two protons are found by Rietveld refinement using a new suitable non-Fourier based strategy, for which GSAS and FullProf yield very similar results. Our X-ray result agrees with the previous neutron study for one proton site only, prompting us to reinvestigate the neutron data. A second new and distinct non Fourier-based strategy coupled with GSAS is used to tackle the latter data and indeed confirms the US results. Whilst the reasons for this X-Ray vs Neutron discrepancy can only be guessed at this stage, the use of the two related proton-finding strategies could be extended beyond our specific study.
Physical Review Letters, 2002
By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously la... more By means of polarized neutron diffraction in a magnetic field of 7.0 T at 1.6 K an anomalously large magnetization density is observed on the in-plane oxygen in Ca1.5Sr0.5RuO4. Field-induced moments of different ions are determined by refinement on the flipping ratios, yielding µRu = 0.346(11) µB, µO1 = 0.076(6) µB and µO2 = 0.009(6) µB. The moment on the oxygen arises from the strong hybridization between the Ru-4d and O-2p orbitals. The maximum entropy magnetization density reconstruction reveals a strongly anisotropic density at the Ru site, consistent with the distribution of the xy (t2g band) d-orbitals.
Physica Status Solidi (a), 1993
Powder neutron diffraction measurements are made on (CD,ND,),MnCl, (d-MAMC) as a function of both... more Powder neutron diffraction measurements are made on (CD,ND,),MnCl, (d-MAMC) as a function of both pressure ((2 to 25) x 10' Pa) and temperature (1.4 to 300 K). The P, T phase diagram, including a new high pressure (HP) phase, is probably of the same kind as that determined previously by Mokhlisse and Couzi for the cadmium homologue. The H P phase of d-MAMC is triclinic (pseudomonoclinic). Magnetic transitions are also reported at TN % 44 K (P = 2 x 10' Pa), occurring in the monoclinic low temperature (MLT) phase, and TN % 50 K (P = 25 x lo8 Pa) occurring in the H P phase. Des mesures de diffraction des neutrons sont rtaliskes sur des Cchantillons polycristallins de (CD,ND,),MnCI, (d-MAMC) en fonction de la pression ((2 a 25) x 10' Pa) et de la temperature (1.4 a 300 K). Le diagramme de phase P, T faisant apparaitre une phase nouvelle sous haute pression (HP) est probablement de mime type que celui ttabli prkckdemment sur le compost homologue du cadmium par Mokhlisse et Couzi. La phase HP du d-MAMC est triclinique (pseudo-monoclinique). Des transitions de phase magnttiques sont mises en tvidence dans la phase MLT a TN x 44 K (P = 2 x 10' Pa) et dans la phase H P a TN N 50 K (P = 25 x lo8 Pa).
Physica B: Condensed Matter, 1997
ABSTRACT