Pr–Co-based intermetallic compounds are candidates for permanent magnets and magnetocaloric effect. Samples have been synthesized by ball milling method with a subsequent fast annealing treatment. While the long-range order obtained by standard X-ray powder diffraction is commonly used to describe the structure and try to understand the exceptional properties of these materials, it is necessary to get a better knowledge of the local environment around each component using local probes. In the iron-substituted materials PrCo\(_{3-x}\)Fe\(_x\), the purpose is to find the substitution of cobalt by iron site. Since the relative concentration in iron is not favorable to Mössbauer studies. Magnetic measurements and magnetocaloric effect were performed using magnetometer measurements. The optimum extrinsic magnetic properties have been obtained for Pr\(_5\)Co\(_{19}\) with a coercivity of 1.5 T at room temperature. Furthermore, these uniaxial anisotropic compounds exhibit a large magnetic entropy change at Curie temperature. \(\Delta S_\text {max}\) is equal to 5.2 J/(kg K) under low magnetic field of 0–1 T. These results indicate that these nanomaterials are suitable for permanent magnet applications and for magnetic refrigeration.

Ecological rehabilitation of degraded mining sites is necessary and possible by reintroducing pioneer manganese-accumulating plants. From the Mn-enriched biomass, our group has developed a process to recycle plant-derived metallic elements into innovative polymetallic catalysts, called Eco-Mn ecocatalysts. These first biosourced Mn-rich catalysts have demonstrated competitive catalytic activity in green organic synthesis. To expand the use of these catalysts in organic chemistry, their catalytic activity has to be correlated with their structure and properties. Thus, we put forward for the first time an extensive structural study of Eco-Mn catalysts, including composition analysis, crystalline structure analysis, and chemical environment around active catalytic center (manganese and iron) analysis. Density Functional Theory (DFT) calculations support our conclusions. Finally, this study highlights the peculiar vegetal footprint of Eco-Mn catalysts. (C) 2019 Elsevier Ltd. All rights reserved.

Nanocrystalline PrCo3-xFex(x <= 1) powder samples were synthesized by high energy milling and subsequent annealing at 1023 K for 30 min. The samples crystallize in the PuNi3-type structure (space group R (3) over barm) for x < 1, confirmed by means of X-ray diffraction. In order to explain the original magnetic properties of these compounds and for the determination of the exchange interaction in theoretical models, the Fe and Co sites and occupancies in the crystallographic structures are required. However, standard XRD can not be used to determine Fe substitution sites, because Co and Fe have too close X-ray atomic scattering factors. Results from neutron diffraction and electronic band structure calculations from our previous works were incomplete or limited. Consequently, we give in this study the characterization of the local structure by X-ray absorption spectroscopy (EXAFS) at the iron K edge. By this method, and if we assume a unique preferential site, it was determined that Fe atoms preferably occupy the 18h site. In order to obtain this result, a coordination sphere around Fe sites of R = 5.2 angstrom had to be considered in order to find sufficient local differences between the possible sites (18h, 6c and 3b). Furthermore, we provide complementary magnetic properties measurements for PrCo3-xFex (x <= 0.75) such as the coercive field H-C, which decreases with iron content from 12 kOe for PrCo3 to 1.5 kOe for PrCo2.25Fe0.75. The magnetization at saturation M-S increases from 69 A m(2)/kg to 89 A m(2)/kg and the calculated anisotropy field H-alpha decreases from 15.6 kOe to 11.2 kOe for the same compositions.

A large data set of XAS (X-ray Absorption Spectroscopy) Manganese K-edge spectra has been collected operando and studied upon the electrochemical oxidation of the promising Li-ion battery anode material Li7MnN4. Using chemometric tools such as PCA (Principal Component Analysis) and MCR-ALS (Multivariate Curve resolution - Alternating Least Squares), three independent environment spectra were insulated. Based on the faradaic yield and well-chosen comparison of absorption spectrum energies within the frame of the coordination charge model, these environments were ascribed to unusual oxidation states allowed by nitride chemistry at a low potential (∼1.2 V vs. Li+/Li), i.e. Mn5+ (3d2), Mn6+ (3d1) and Mn7+ (3d0). Also, their relative amounts are discussed with regard to the long-range structural variation which can be simply described by two successive biphasic domains followed by a solid-solution behaviour. Gathering this long-range and local structure information provides a complete picture of the redox mechanisms occurring in Li7MnN4.

This paper reports on the structural characterization of Pb1−xBaxZr0.40Ti0.60O3 (PBZT) ferroelectric ceramic compositions prepared by the conventional solid state reaction method. X-ray absorption spectroscopy (XAS) and Raman spectroscopy were used in the probing of the local structure of PBZT samples that exhibit a normal or relaxor ferroelectric behavior. They showed a considerable local disorder around Zr and Pb atoms in the samples of tetragonal or cubic long-range order symmetry. The intensity of the E(TO3) mode in the Raman spectra of PBZT relaxor samples remains constant at temperatures lower than Tm, which has proven the stabilization of the correlation process between nanodomains.

Nanocrystalline Pr-2 Co7-x Fe-x (x <= 3.5) powder was synthesized by high energy milling and was subsequently annealed at 973 K for 30 min. Their crystalline structures were investigated by means of X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM). Magnetic properties were also studied at room temperature and 10 K as a function of the iron composition.This compounds structure depends on the iron content; for x <= 1 they crystallize in the Ce-2 Ni-7-type hexagonal structure (space group: P6(3)/mmc). For 1 < x <= 3, we observe a mixture of three phases, Pr-2(Co,Fe)(7), Pr(Co,Fe)(3) and Pr-2(Co,Fe)(17) while for larger values of x the Pr-2(Co,Fe)(7) phase disappears completely. Since the substitution of cobalt by iron in a pure Pr-2 Co7-x Fex phase is limited to x <= 1, a site preference can be suggested. Unfortunately standard XRD cannot be used unambiguously because Co and Fe have too close normal X-ray atomic scattering factors. Among the local and Fe selective available experimental methods, we have chosen to explore the P6(3)/mmc space group Wyckoff positions for iron by EXAFS at the Fe edge. This study shows that the local iron radial distribution function is much larger than expected for all the specific sites, at least two Fe-Pr distances, except for 12k which gives the best fit. A preferential substitution of cobalt by iron in Ref. 12k site is coherent with (i) the EXAFS result (ii) the substitution rate x < 1 (iii) the anisotropic increase of the crystal cell parameters. A mixture of 12k, 6h and 2a cannot be excluded. However, if we assume a unique preferential site, 12k is the only solution.For x <= 1, the magnetocryslalline anisotropy is observed in Pr-2 Co7-x Fex alloys with fairly strong anisotropy fields at room temperature in range from 123 to 136 kOe for x = 0 and x = 1, respectively. For x > 1, the magnetocrystalline anisotropy field of the 2:17 phase is lower than that of the 2:7 phase, which causes a further reduction in anisotropy and coercivity. (C) 2016 Elsevier B.V. All rights reserved.

In this study, the electronic and local structures of Pb1-xBaxZr0.40Ti0.60O3 ferroelectric ceramic samples were characterized using X-ray absorption near-edge structure (XANES) measurements. The analysis of XANES spectra collected at the Ti K-and L-edges showed that the substitution of Pb by Ba leads to a decrease in the local distortion around the Ti atoms in the TiO6 octahedron. The analysis of O K-edge XANES spectra and density of states ab initio calculations showed that the hybridization between the O 2p and Pb 6sp states is related to the displacement of Ti atoms in the TiO6 octahedra. Based on these results, it is possible to determine that the degree of ferroelectricity in these samples and the manifestation of relaxor behavior are directly related to the weakening of O 2p and Pb 6sp hybridization. (C) 2015 Elsevier B.V. All rights reserved.

Fourier transform magnitude of Cu K-edge absorption spectra before (300 K) and after (550 K) reduction.

The influence of cobalt substitution on the local structural changes around Co atoms in the layered lithium nitridocobaltates Li(3-2x)Co(x)N for 0.05 ≤ x ≤ 0.44 is investigated using Co K-edge X-ray absorption spectroscopy (EXAFS and XANES). The Co-N bond length in Li(3-2x)Co(x)N compounds is obtained vs x by performing EXAFS fitting and found to be shorter (1.80 Å) than for x = 0 (Li3N), and its value does not change with x. A comparison of EXAFS data with XRD results is discussed. We show that the continuous decrease of interlayer distance versus Co content (x), described from XRD data, accounts for an average of the Co-N and Li-N distances, weighted by the number of these bond lengths. In addition, the present work supports the proposal that the Li1b-N bonds contract with x due to a significant increase of Coulombic attractive forces locally induced by the progressive Li(+)/Co(2+) substitution. XRD studies suggested that divalent Co ions bond to two nitrogen in Li(3-2x)Co(x)N. Although additional works are still needed to prove its valence, the present XAFS findings complements the local structure found by XRD, in good accord with the electrochemical properties previously reported.

This paper reports on a multi-edge X-ray absorption analysis to elucidate how the substitution of Ti4+ by Zr4+ ions acts on the local order structure and on the O 2p hybridization states of Ba0.9Ca0.1Ti1−xZrxO3 (BCZT) lead-free ceramic compounds, inducing a ferroelectric evolution from a normal to a relaxor character. Ti, Ba, Zr and O X-ray absorption spectra were measured to probe the local and electronic structure of BCZT samples that exhibit a normal (x<0.18) or relaxor (x⩾0.18) ferroelectric character. X-ray absorption near edge structure results show that the local symmetry and distortion of TiO6, ZrO6 and BaO12 units are not significantly affected by the Ti/Zr ratio, the ferroelectric character or the long-range order symmetry. The assignment of the ab initio density of states associated with the O K-edge enabled a correlation between the decrease in the hybridization between O 2p and Ti 3d states and the ferroelectric character evolution of the BCZT samples. The hybridization states in the ferroelectric relaxor samples exhibit a more symmetric spatial configuration, as occurs with long-range symmetry.

This paper reports on the structural characterization of Pb1-xLaxZr0.40Ti0.60O3 (PLZT) ferroelectric ceramic compositions prepared by the conventional solid state reaction method. X-ray absorption spectroscopy (XAS) and Raman spectroscopy were used to probe the local structure of PLZT samples that exhibits a normal and relaxor ferroelectric behavior. From the Zr K-edge and Pb L-III-edge EXAFS spectra, a considerable dissymmetry of Zr and Pb sites was observed in all samples, including those showing a long-range order cubic symmetry and a relaxor behavior. The Raman spectroscopy results confirmed the existence of a local disorder in all PLZT samples through the observation of Raman active vibrational modes. The variation in the intensity of the E(TO3) mode in the PLZT relaxor samples indicates that the process of correlation between nanodomains stabilizes at temperatures lower than T-m. (c) 2013 Elsevier B.V. All rights reserved.

EXAFS fit applied to asymmetric systems may imply the fit of parameters for many scattering paths. We illustrate on some examples how fitting too many independent DWs may lead to incorrect distances and mask some structural details. We question the physical meaning of the fitted DW values and we propose some ideas to avoid this problem.

Instituto de Geociencias e Ciencias Exatas Departamento de Fisica Universidade Estadual Paulista, Rio Claro, SP, 13506-900

In the frame of research on new metallic hydrides as conversion reaction materials for negative electrodes of Li-ion batteries, the MgFe2H6 complex hydride has been investigated in and ex situ using XRD, XAS and magnetic measurements at different states: initially ball milled complex hydride (CH), electrochemically desorbed (ED) and thermally desorbed (TD). Fe-H bonding is clearly evidenced by EXAFS in the CH sample. It is also observed that the electrochemical reaction leads to a nanocrystalline state that needs local probe analyses to be fully investigated and interpreted. From the XAS and magnetic data, the different routes (ED and TD) for dehydrogenation of the complex hydride are compared. For both electrochemically and thermally driven reactions, the hydrogen depletion from Mg2FeH6 hydride leads to decomposition into its constituting elements Mg and Fe. However, different Fe structures are observed: bulk alpha-Fe and amorphous Fe nanoparticles for TD and ED samples, respectively.

One of the main pitfalls in EXAFS fitting is correlation among parameters, which can lead to unreliable fits. The use of theoretical Debye-Waller factors (DWs) is a promising way to reduce the number of fitted parameters. When working with molecular dynamics, it is not only possible to evaluate DWs from the statistical distributions issued from the trajectory but also to estimate the distribution anharmonicity, and to compute simulated average EXAFS spectra that can be fitted as experimental ones, in order to assess the ability of EXAFS fitting to recover information on DWs, as well as other structural and spectroscopical parameters. The case studied is oxaliplatin, a third generation anticancer drug. The structural information and the simulated average spectra were derived from a Car-Parrinello molecular dynamics (CP-MD) trajectory of a compound closely related to oxaliplatin. We present the DWs issued from this simulation and their use, by taking their theoretical absolute values (no DW fitted) or their ratios (one DW fitted). In this second approach, the fit of oxaliplatin experimental spectra leads to DWs values very close to the theoretical ones. This shows that the CP-MD trajectory provides a good representation of the distance distributions for oxaliplatin. Transferability of oxaliplatin DWs, for all relevant single and multiple scattering paths, to closely related compounds is proven for the case of bis(oxalato)platinum(II) and bis(ethylene diamine)platinum(II).

This work presents a comprehensive study about the influence of Ba-substitution on the structural and ferroelectric properties of Pb1-xBaxZr0.40Ti0.60O3 (PBZT) ceramic system. Pb1-xBaxZr0.40Ti0.60O3 ceramic samples were then prepared by solid state reaction method and characterized as a function of composition and temperature by X-ray diffraction (XRD) and impedance spectroscopy techniques. The dielectric measurements show that the substitution of Pb2+ for Ba2+ ions leads to a diffuse behavior of the dielectric permittivity curves for all samples and that only the x = 0.50 sample presents a typical relaxor behavior. In good agreement with dielectric measurements, the structural phase transition study showed a phase transition from a tetragonal structure with P4mm space group to a cubic structure with Pm-3m space group for all samples, except for the x = 0.50 sample were a cubic structure was observed in the complete temperature interval measured.

Nanostructured Pb0.90Ba0.10Zr0.40Ti0.60O3 dense ceramics presenting an average grain size of 62 +/- 5 nm was prepared by the polymeric precursor method and using the spark plasma sintering technique. The dielectric permittivity curves versus temperature exhibit broad anomaly, indicative of a diffuse phase transition. This result can be explained by the spread of Curie temperatures which are expected to depend on the degree of tetragonality related to the grain size distribution. A pronounced decrease in the maximum of the dielectric permittivity value is attributed to the existence of a large amount of grain boundaries which are non-ferroelectric regions.

The Pb 1− x La x Zr y Ti 1− y O 3 system is a perovskite ABO 3 structured material which presents ferroelectric properties and has been used as capacitors, actuators, transducers and electro-optic devices. In this paper, we describe the synthesis and the characterization of Pb 0.89 La 0.11 Zr 0.40 Ti 0.60 O 3 (PLZT11) nanostructured material. The precursor polymeric method and the spark plasma sintering technique were respectively used to prepare ceramic samples. In order to compare the effect of grain size, microcrystalline PLZT11 ceramic samples were also prepared. PLZT11 samples were characterized by X-ray diffraction technique which results show a reduction on the degree of tetragonality as the average grain size decreases. Moreover, the grain size decrease to a nanometer range induces a diffuse behavior on the dielectric permittivity curves as a function of the temperature and a reduction on the dielectric permittivity magnitude. Furthermore, the large number of grain boundaries due to the nanometer size gives rise to a dielectric anomaly.