By means of neutron powder diffraction, we investigated the effect of the polar Bi$^{3+}$ ion on ... more By means of neutron powder diffraction, we investigated the effect of the polar Bi$^{3+}$ ion on the magnetic ordering of the Mn$^{3+}$ ions in BiMn$_3$Mn$_4$O$_{12}$, the counterpart with \textit{quadruple} perovskite structure of the \textit{simple} perovskite BiMnO$_3$. The data are consistent with a \textit{noncentrosymmetric} spacegroup $Im$ which contrasts the \textit{centrosymmetric} one $I2/m$ previously reported for the isovalent and isomorphic compound LaMn$_3$Mn$_4$O$_{12}$, which gives evidence of a Bi$^{3+}$-induced polarization of the lattice. At low temperature, the two Mn$^{3+}$ sublattices of the $A'$ and $B$ sites order antiferromagnetically (AFM) in an independent manner at 25 and 55 K, similarly to the case of LaMn$_3$Mn$_4$O$_{12}$. However, both magnetic structures of BiMn$_3$Mn$_4$O$_{12}$ radically differ from those of LaMn$_3$Mn$_4$O$_{12}$. In BiMn$_3$Mn$_4$O$_{12}$ the moments $\textbf{M}_{A'}$ of the $A'$ sites form an anti-body AFM structure,...
High energy mechanical milling (HEM) is widely used in the pharmaceutical industry as a top down ... more High energy mechanical milling (HEM) is widely used in the pharmaceutical industry as a top down micronisation process to improve the therapeutic properties and in particular the dissolution of API and excipient molecules. However, milling can also change the physical state and lead to solid state amorphization, phase transformations, etc... Little is known about the mechanisms at play in this process. Of vital importance for the pharmaceutical industry is the understanding of what is controlling the formation and particularly the stability of amorphous materials processed in this way. For example recrystallization can modify their therapeutic properties and must be controlled during e.g. storage periods. Providing structural and microstructural information whatever the sample crystallinity, PDF analysis is particularly well suited to study such milled samples and their recrystallization process. We are using PDF analysis of synchrotron data to investigate the HEM amorphization of t...
Phase mapping and quantitative analysis of complex cultural heritage materials thanks to multivar... more Phase mapping and quantitative analysis of complex cultural heritage materials thanks to multivariate analysis applied to XRD-CT data.
The electrochemical activation of Li2O in densified nano-Li2MnO3 is responsible for the large rev... more The electrochemical activation of Li2O in densified nano-Li2MnO3 is responsible for the large reversible capacity (290 mA h g−1) in this system.
Correction for ‘Reversible densification in nano-Li2MnO3 cation disordered rock-salt Li-ion batte... more Correction for ‘Reversible densification in nano-Li2MnO3 cation disordered rock-salt Li-ion battery cathodes’ by Maria Diaz-Lopez et al., J. Mater. Chem. A, 2020, 8, 10998–11010, DOI: 10.1039/d0ta03372c.
Low mechanical pressure on amorphous gold thiolate coordination polymers allows the formation of ... more Low mechanical pressure on amorphous gold thiolate coordination polymers allows the formation of transparent and red emissive glasses.
We have investigated the solid-state transformation of anhydrous β-d-mannitol upon milling using ... more We have investigated the solid-state transformation of anhydrous β-d-mannitol upon milling using synchrotron X-ray powder diffraction. The 1720 diffraction patterns, collected in real time during the operation of the mill (6 h), have been analyzed by sequential Rietveld refinements. From this analysis we confirm that a polymorphic conversion has occurred from the form β toward the form α. Moreover, the quantification and the microstructural analysis of both polymorphs have allowed obtaining new results: (i) the kinetic of the transformation is characterized by a sigmoidal shape, (ii) little microstructural evolution occurs during the solid-state transformation, (iii) no intermediate amorphous phase, preceding the transformation toward the metastable crystalline α phase, can be detected. A comparison in depth of the two crystal structures is given, and two models are proposed in order to explain this direct conversion β → α.
Abstract The study of cultural heritage objects represents a challenge for materials sciences, be... more Abstract The study of cultural heritage objects represents a challenge for materials sciences, because of their intrinsic complexity as well as because of their rare and precious nature, which requires the use of non-destructive methods. One of the major difficulties encountered by the methods of structural analysis of these materials is the presence of mixtures of crystallized and amorphous phases, the conventional methods of crystallography being poorly adapted to the latter. Here we present the Pair Distribution Function analysis method, which based on diffraction data, allows access to the identification, microstructural characterization and quantification of phases constituting a complex mixture, independently of their amorphous or crystalline character. Two recent examples will be presented to illustrate the use of this method in studies of cultural heritage materials.
The superconducting oxide BaPb1-xBixO3, discovered in 1975 (ref. 1), is an exotic system having a... more The superconducting oxide BaPb1-xBixO3, discovered in 1975 (ref. 1), is an exotic system having an unusually high transition temperature (Tc) of ~12K, despite a relatively low density of states at the Fermi level. The subsequent prediction that dopingthe electronically inactive barium donor sites, instead ofthe bismuth sites, might induce superconductivity with a higher Tc led to the discovery in 1988
The room-temperature structure of an untwinned orthorhombic YBazCu307 single crystal was determin... more The room-temperature structure of an untwinned orthorhombic YBazCu307 single crystal was determined from x-ray-diffraction intensity data. The crystal was grown by the self-flux method, and detwinned by the application of a uniaxial stress under flowing oxygen at 450 C. A superconducting transition of 91.3 K (hT, =1.4 K) was measured. Precession photographs showed no evidence of twinning, and no line splitting or broadening was apparent in high-angle reflections. The crystal structure was refined in the Pmmm space group, with a=3.8184(3), b=3.8857(2), and c=11.701(1) A. The overall oxygen content was determined to be 6.877(8). Electron-density Fourier maps and the anisotropic temperature factors do not support the double-well apical oxygen model proposed from extended xray absorption fine structure data. Distortions of the electron density of the planar Cu sites suggest the possibility of a nonhomogeneous Cu02 conducting plane. The anomalous thermal parameters of the chain oxygens appear to result from dynamic disorder rather than a buckling of the Cu-0 chains. Although a number of different experiments have suggested the presence of a split axial oxygen site in superconducting YBa2Cu307, there has been no direct evidence of two distinct positions from x-ray-or neutrondiffraction-structural characterizations. Recent Cu Kedge polarized extended x-ray absorption fine structure (EXAFS) measurements' on YBa2Cu307 have been interpreted to reveal two egually populated axial oxygen sites separated by =0. 13 A, with the separation distance decreasing slightly near T,. The two sites have been described by a double-well potential relating the electronic degrees of freedom of the superconducting transition to the elastic degrees of freedom of the ionic motion. These results suggest that the charge transfer from the chain Cu
In situ x-ray-diffraction measurements under high pressure ͑P up to 20 GPa͒ have been used to stu... more In situ x-ray-diffraction measurements under high pressure ͑P up to 20 GPa͒ have been used to study structural changes in the rhombohedral and the tetragonal phases of CaSi 2 at room temperature. Lattice parameters of the tetragonal phase regularly change with increasing pressure while the rhombohedral phase undergoes two structural phase transitions: A trigonal structure is observed for 9Ͻ PϽ16 GPa and a new AlB 2-like phase appears for PϾ16 GPa. These observations lead to ascribe the appearance of superconductivity to the trigonal phase while the highest T c 's can be related to the transition towards the AlB 2-like phase that differs from the low-pressure phases by the almost planar bonds of silicon.
We have investigated the magnetic and magnetoelectric properties of CaMnGe 2 O 6 by means of powd... more We have investigated the magnetic and magnetoelectric properties of CaMnGe 2 O 6 by means of powder neutron diffraction, magnetic susceptibility, heat capacity, and electrical polarization measurements. The presence of one-dimensional short-range magnetic correlations within the MnO 6 octahedra chains well above long-range antiferromagnetic ordering (15 K) was evidenced. A one-dimensional antiferromagnetic correlation model along the zigzag chains was developed to fit the diffuse magnetic scattering. The linear magnetoelectric effect and pertinent ferrotoroidicity, allowed by the magnetic symmetry (C2 /c), have been verified experimentally and theoretically.
Determining the formation and growth mechanism of bimetallic nanoparticles (NPs) with atomic deta... more Determining the formation and growth mechanism of bimetallic nanoparticles (NPs) with atomic detail is fundamental to synthesize efficient "catalysts by design". However, an understanding of the elementary steps which take place during their synthesis remains elusive. Herein, we have exploited scanning transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy, operando wide angle and small-angle X-ray scattering, and electrochemistry to unveil the formation and growth mechanism of hollow PtNi/C NPs. Such NPs, composed of a PtNi shell surrounding a nanoscale void, catalyze efficiently and sustainably the oxygen reduction reaction (ORR) in an acidic electrolyte. Our step-by-step study reveals that (i) Ni-rich/C NPs form first, before being embedded in a NixByOz shell, (ii) the combined action of galvanic displacement and the nanoscale Kirkendall effect then results in the sequential formation of Ni-rich core@Pt-rich/C shell and ultimately hollow PtNi/C...
Single-crystal x-ray and electron diffraction studies established a direct relationship between l... more Single-crystal x-ray and electron diffraction studies established a direct relationship between lithium content, crystal structure, niobium valence, and the appearance of superconductivity in the system Li1-xNbO2. The induction of superconductivity by removal of x~0.3 lithium is accompanied by the appearance of a superstructure with unit cell a×b×2c, where a×b×c is the unit cell of the nonsuperconductor LiNbO2. Detailed structural analysis, based on both the main and superlattice reflections, demonstrated that the superconductor Li1-xNbO2 [x~0.79(9), Tc~5.5 K] has P3¯m1 symmetry, with interlayer ordering of lithium vacancies and weakly distorted [NbO2] network. As a result of this distortion, Nb cations of the different layers have different valences (3.7+ and 2.6+).
By means of neutron powder diffraction, we investigated the effect of the polar Bi$^{3+}$ ion on ... more By means of neutron powder diffraction, we investigated the effect of the polar Bi$^{3+}$ ion on the magnetic ordering of the Mn$^{3+}$ ions in BiMn$_3$Mn$_4$O$_{12}$, the counterpart with \textit{quadruple} perovskite structure of the \textit{simple} perovskite BiMnO$_3$. The data are consistent with a \textit{noncentrosymmetric} spacegroup $Im$ which contrasts the \textit{centrosymmetric} one $I2/m$ previously reported for the isovalent and isomorphic compound LaMn$_3$Mn$_4$O$_{12}$, which gives evidence of a Bi$^{3+}$-induced polarization of the lattice. At low temperature, the two Mn$^{3+}$ sublattices of the $A'$ and $B$ sites order antiferromagnetically (AFM) in an independent manner at 25 and 55 K, similarly to the case of LaMn$_3$Mn$_4$O$_{12}$. However, both magnetic structures of BiMn$_3$Mn$_4$O$_{12}$ radically differ from those of LaMn$_3$Mn$_4$O$_{12}$. In BiMn$_3$Mn$_4$O$_{12}$ the moments $\textbf{M}_{A'}$ of the $A'$ sites form an anti-body AFM structure,...
High energy mechanical milling (HEM) is widely used in the pharmaceutical industry as a top down ... more High energy mechanical milling (HEM) is widely used in the pharmaceutical industry as a top down micronisation process to improve the therapeutic properties and in particular the dissolution of API and excipient molecules. However, milling can also change the physical state and lead to solid state amorphization, phase transformations, etc... Little is known about the mechanisms at play in this process. Of vital importance for the pharmaceutical industry is the understanding of what is controlling the formation and particularly the stability of amorphous materials processed in this way. For example recrystallization can modify their therapeutic properties and must be controlled during e.g. storage periods. Providing structural and microstructural information whatever the sample crystallinity, PDF analysis is particularly well suited to study such milled samples and their recrystallization process. We are using PDF analysis of synchrotron data to investigate the HEM amorphization of t...
Phase mapping and quantitative analysis of complex cultural heritage materials thanks to multivar... more Phase mapping and quantitative analysis of complex cultural heritage materials thanks to multivariate analysis applied to XRD-CT data.
The electrochemical activation of Li2O in densified nano-Li2MnO3 is responsible for the large rev... more The electrochemical activation of Li2O in densified nano-Li2MnO3 is responsible for the large reversible capacity (290 mA h g−1) in this system.
Correction for ‘Reversible densification in nano-Li2MnO3 cation disordered rock-salt Li-ion batte... more Correction for ‘Reversible densification in nano-Li2MnO3 cation disordered rock-salt Li-ion battery cathodes’ by Maria Diaz-Lopez et al., J. Mater. Chem. A, 2020, 8, 10998–11010, DOI: 10.1039/d0ta03372c.
Low mechanical pressure on amorphous gold thiolate coordination polymers allows the formation of ... more Low mechanical pressure on amorphous gold thiolate coordination polymers allows the formation of transparent and red emissive glasses.
We have investigated the solid-state transformation of anhydrous β-d-mannitol upon milling using ... more We have investigated the solid-state transformation of anhydrous β-d-mannitol upon milling using synchrotron X-ray powder diffraction. The 1720 diffraction patterns, collected in real time during the operation of the mill (6 h), have been analyzed by sequential Rietveld refinements. From this analysis we confirm that a polymorphic conversion has occurred from the form β toward the form α. Moreover, the quantification and the microstructural analysis of both polymorphs have allowed obtaining new results: (i) the kinetic of the transformation is characterized by a sigmoidal shape, (ii) little microstructural evolution occurs during the solid-state transformation, (iii) no intermediate amorphous phase, preceding the transformation toward the metastable crystalline α phase, can be detected. A comparison in depth of the two crystal structures is given, and two models are proposed in order to explain this direct conversion β → α.
Abstract The study of cultural heritage objects represents a challenge for materials sciences, be... more Abstract The study of cultural heritage objects represents a challenge for materials sciences, because of their intrinsic complexity as well as because of their rare and precious nature, which requires the use of non-destructive methods. One of the major difficulties encountered by the methods of structural analysis of these materials is the presence of mixtures of crystallized and amorphous phases, the conventional methods of crystallography being poorly adapted to the latter. Here we present the Pair Distribution Function analysis method, which based on diffraction data, allows access to the identification, microstructural characterization and quantification of phases constituting a complex mixture, independently of their amorphous or crystalline character. Two recent examples will be presented to illustrate the use of this method in studies of cultural heritage materials.
The superconducting oxide BaPb1-xBixO3, discovered in 1975 (ref. 1), is an exotic system having a... more The superconducting oxide BaPb1-xBixO3, discovered in 1975 (ref. 1), is an exotic system having an unusually high transition temperature (Tc) of ~12K, despite a relatively low density of states at the Fermi level. The subsequent prediction that dopingthe electronically inactive barium donor sites, instead ofthe bismuth sites, might induce superconductivity with a higher Tc led to the discovery in 1988
The room-temperature structure of an untwinned orthorhombic YBazCu307 single crystal was determin... more The room-temperature structure of an untwinned orthorhombic YBazCu307 single crystal was determined from x-ray-diffraction intensity data. The crystal was grown by the self-flux method, and detwinned by the application of a uniaxial stress under flowing oxygen at 450 C. A superconducting transition of 91.3 K (hT, =1.4 K) was measured. Precession photographs showed no evidence of twinning, and no line splitting or broadening was apparent in high-angle reflections. The crystal structure was refined in the Pmmm space group, with a=3.8184(3), b=3.8857(2), and c=11.701(1) A. The overall oxygen content was determined to be 6.877(8). Electron-density Fourier maps and the anisotropic temperature factors do not support the double-well apical oxygen model proposed from extended xray absorption fine structure data. Distortions of the electron density of the planar Cu sites suggest the possibility of a nonhomogeneous Cu02 conducting plane. The anomalous thermal parameters of the chain oxygens appear to result from dynamic disorder rather than a buckling of the Cu-0 chains. Although a number of different experiments have suggested the presence of a split axial oxygen site in superconducting YBa2Cu307, there has been no direct evidence of two distinct positions from x-ray-or neutrondiffraction-structural characterizations. Recent Cu Kedge polarized extended x-ray absorption fine structure (EXAFS) measurements' on YBa2Cu307 have been interpreted to reveal two egually populated axial oxygen sites separated by =0. 13 A, with the separation distance decreasing slightly near T,. The two sites have been described by a double-well potential relating the electronic degrees of freedom of the superconducting transition to the elastic degrees of freedom of the ionic motion. These results suggest that the charge transfer from the chain Cu
In situ x-ray-diffraction measurements under high pressure ͑P up to 20 GPa͒ have been used to stu... more In situ x-ray-diffraction measurements under high pressure ͑P up to 20 GPa͒ have been used to study structural changes in the rhombohedral and the tetragonal phases of CaSi 2 at room temperature. Lattice parameters of the tetragonal phase regularly change with increasing pressure while the rhombohedral phase undergoes two structural phase transitions: A trigonal structure is observed for 9Ͻ PϽ16 GPa and a new AlB 2-like phase appears for PϾ16 GPa. These observations lead to ascribe the appearance of superconductivity to the trigonal phase while the highest T c 's can be related to the transition towards the AlB 2-like phase that differs from the low-pressure phases by the almost planar bonds of silicon.
We have investigated the magnetic and magnetoelectric properties of CaMnGe 2 O 6 by means of powd... more We have investigated the magnetic and magnetoelectric properties of CaMnGe 2 O 6 by means of powder neutron diffraction, magnetic susceptibility, heat capacity, and electrical polarization measurements. The presence of one-dimensional short-range magnetic correlations within the MnO 6 octahedra chains well above long-range antiferromagnetic ordering (15 K) was evidenced. A one-dimensional antiferromagnetic correlation model along the zigzag chains was developed to fit the diffuse magnetic scattering. The linear magnetoelectric effect and pertinent ferrotoroidicity, allowed by the magnetic symmetry (C2 /c), have been verified experimentally and theoretically.
Determining the formation and growth mechanism of bimetallic nanoparticles (NPs) with atomic deta... more Determining the formation and growth mechanism of bimetallic nanoparticles (NPs) with atomic detail is fundamental to synthesize efficient "catalysts by design". However, an understanding of the elementary steps which take place during their synthesis remains elusive. Herein, we have exploited scanning transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy, operando wide angle and small-angle X-ray scattering, and electrochemistry to unveil the formation and growth mechanism of hollow PtNi/C NPs. Such NPs, composed of a PtNi shell surrounding a nanoscale void, catalyze efficiently and sustainably the oxygen reduction reaction (ORR) in an acidic electrolyte. Our step-by-step study reveals that (i) Ni-rich/C NPs form first, before being embedded in a NixByOz shell, (ii) the combined action of galvanic displacement and the nanoscale Kirkendall effect then results in the sequential formation of Ni-rich core@Pt-rich/C shell and ultimately hollow PtNi/C...
Single-crystal x-ray and electron diffraction studies established a direct relationship between l... more Single-crystal x-ray and electron diffraction studies established a direct relationship between lithium content, crystal structure, niobium valence, and the appearance of superconductivity in the system Li1-xNbO2. The induction of superconductivity by removal of x~0.3 lithium is accompanied by the appearance of a superstructure with unit cell a×b×2c, where a×b×c is the unit cell of the nonsuperconductor LiNbO2. Detailed structural analysis, based on both the main and superlattice reflections, demonstrated that the superconductor Li1-xNbO2 [x~0.79(9), Tc~5.5 K] has P3¯m1 symmetry, with interlayer ordering of lithium vacancies and weakly distorted [NbO2] network. As a result of this distortion, Nb cations of the different layers have different valences (3.7+ and 2.6+).
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Papers by Pierre Bordet