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The purpose of the study was to investigate the synthesis of economic calcium phosphate powders from recycled oyster shells, using a ball milling method. The oyster shell powder and a calcium pyrophosphate powder were used as starting materials and ball milled, then heat treated at 1,050°C for 5 h to produce calcium phosphate powders through a solid-state reaction. Electrochemically synthesized mesoporous silicon microparticles were then added to the prepared phosphate powders by mechanical mixer. The final powders were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy to analyze their chemical composition and determine the most suitable process conditions. The biocompatibility of the produced powders was also tested in vitro using murine cells and the results showed good biocompatibility.

This study reports a sustainable approach for developing electrodes for microsupercapacitors. This approach includes the synthesis of TiO2 nanoparticles via a green sol–gel method and the deposition of thin films of that electrochemically active material on three-dimensional (3D) Si substrates with a high area enlargement factor (AEF) via a simple, fast, and inexpensive spin-coating pathway. The thickness of the film was first optimized via its deposition over two-dimensional (2D) substrates to achieve high capacitances to provide high energy density but also to deliver a good rate capability to ensure the power density required for a supercapacitor device. A film thickness of ~120 nm realizes the best compromise between the electronic/ionic conductivity and capacitance in a supercapacitor device. Such layers of TiO2 were successfully coated onto 3D microstructured substrates with different architectures, such as trenches and pillars, and different aspect ratios. The spin-coating-based route developed here has been established to be superior as, on the one hand, a conformal deposition can be achieved over high AEF subtracts, and on the other hand, the 3D electrodes present higher surface capacitances than those obtained using other deposition techniques. The rate capability and appreciable cyclability ensure a reliable supercapacitor behavior.

The elimination of rubber wastes without affecting the environment is one of the most important challenges of the 21st century waste management. Accordingly, the present work is focused on the recycling of natural rubber (NR) industry waste by means of devulcanization in supercritical carbon dioxide (scCO2) atmosphere. With that aim, a novel device allowing to perform rubber devulcanization was developed. It consists of a triaxial compression reactor integrated into a dynamic hydraulic universal testing machine with a heating chamber. NR industry waste was devulcanized in the mentioned device at different temperatures, in scCO2 by using diphenyl disulfide (DD) as devulcanizing reagent. The devulcanization degree and quality of the treated materials were evaluated by the swelling test combined with the Horikx theory. It was appeared that a successful devulcanization, with almost no degradation, was obtained, and the devulcanization degree reached maximum value of ~90%. Thermogravimetric tests and scanning electron microscopy (SEM) images strengthened these results. Finally, it was concluded that the developed device is appropriate to perform rubber recycling, which contributes to the progress in the environmental protection.

The preservation of heritage is an interdisciplinary challenge which needs the expertise of many scientific disciplines as well as chemistry, physic, historical, etc. In the French Centre-Val de Loire region, most castles were built with both Tuffeau and Richemont stones. In this paper, we analyze some stones samples using both the Nonlinear Time Reversal imaging technique that is able to extract ultrasonic signatures in the the complex weathered Tuffeau stone at 5 MHz, and terahertz/infrared signature (FTIR) of the same sample with the same aging properties. Research has been undertaken to determine the potential of Nonlinear Time Reversal non destructive techniques in symbiosis with classical FTIR and X-ray chemical analysis for revealing the aging and chemical composition of historic stones. Nonlinear Time Reversal techniques are non invasive and non destructive making them suitable for in situ analysis of old stones and old concrete, as it is already made for modern concrete. It is shown that the symbiosis of ultrasound-based multimodal imaging and terahertz methods can provide an important diagnostic tool for cultural heritage applications. Chemical analysis is also necessary, for example, to identify the nature of the weathering and the aging.

The preservation of patrimonial is an interdisciplinary challenge which needing the expertise of many scientific disciplines as well as chemistry, physic, historical, etc. In order to generalize the idea of protection, Non Destructive Testing (NDT) is necessary for cultural heritage protection. The Loire Valley in France has a diversified cultural heritage, including monuments where the mainly construction units is stone. Research has been undertaken to determine the potential of Nonlinear Time Reversal (TR) non destructive techniques in symbiosis with classical FTIR and X-ray chemical analysis for revealing the aging and chemical composition of historic stones. It is shown that the sensitivity of TR based nonlinear ultrasonic methods in symbiosis with high frequency FTIR methods reaches the level of sensitivity for future non-invasive ultrasonic methods applied to cultural heritage.

In order to study the effect of oxygen doping on magnetic correlations in La 2 NiO 4+d , electron spin resonance (ESR) measurements, which allow to characterize the spin fluctuations, have been performed on three compounds with δ = 0.09, 0.12, and 0.17. The ESR parameters anomalies are in relation with charge and spin order in stripes observed by others techniques such as neutron diffraction.

Several approaches based on the sol-gel process have been developed to synthesize YSZ (ZrO2-8%Y2O3) films with controlled porosities and thickness. Thick monolayer (> 10 µm) was obtained from a powder charged polymeric sol using the dip-coating process. This film exhibited porosities after a heat treatment at 1300{degree sign}C during 4 hours in air. These porosities are related to the decomposition of carbonate species formed during the heat-treatment. Dense films with a thickness ranging from 1 to 5 μm were synthesized via the deposition (spin-coating and dip-coating) of a solution containing YSZ nanoparticles. The calcinations temperature influences the films' density and porosity. YSZ films were synthesized on anode support (Ni-YSZ/YSZ) in order to evaluate the microstructure of these films in real fuel cell.

International audience; We used electron spin resonance (ESR) and magnetic susceptibility to study the magnetic correlations in polycrystalline La2NiO4.12 prepared by modified sol–gel method. We observed an evolution of the ESR signal with temperature, from 4 K to 300 K, with marked changes at 220 K and 150 K. Such changes are related to the particular order of holes and spins previously observed in this system by neutron diffraction by other authors. Magnetic susceptibility measurements confirm the charge and spin order temperatures in this composition.

X- and Q-band ESR experiments on ceramics and single crystals of La 2 NiO 4+ δ (0.03 ≤ δ ≤ 0.17) are reported. The observed intrinsic ESR signals were interpreted in terms of ferromagnetic resonance of isolated oxidized nickel species in the lattice. The origin of the ferromagnetic component differs according to the δ value, consistent with the phase diagram and the phenomenon of charge and spin order. The ESR spectra on powders exhibit an anisotropic signal attributed to the presence of a magnetic local field, induced by the external magnetic field applied during the first ESR measurement. For specific value of δ , the ESR spectra show a “multilines signal” from the origin which could be due to the presence of magnetic polarons which are pinned on the surface. An ESR study vs. temperature for a powder sample with δ = 0.16 shows that the linewidth evolution is in relation with the transition from a dynamic stripe to a static stripe state at 160 K. At high temperature ( T > 600 K), a polaronic liquid is observed.

Effects of Pr substitution on the magnetic properties of perovskite manganite Nd0.5Sr0.5MnO3 have been investigated by measurements of electron spin resonance, magnetization, and powder neutron dif...

We studied the magnetic correlations in polycrystalline La2NiO4+δ with δ=0.18 using electron spin resonance (ESR), which is a local magnetic probe, and magnetic susceptibility. Significant magnetic changes were observed around 160 K. Such changes can be related to the particular order of charge and spins present in this compound.

Nd1.67Sr0.33NiO4 polycrystals have been prepared by modified sol–gel method and subsequent annealing. X-ray diffraction analysis, electrical resistivity, magnetic susceptibility and thermal magnetisation have been measured. Rietveld analyses show a tetragonal or pseudo-tetragonal K2NiF4-type structure. The resistivity measurements present a change in conduction mode close to 230 K, which corresponds to the charge ordering temperature. Below this temperature, the material adopts a variable range hopping conduction mode; and above, the conduction follows adiabatic thermal activated mode. The magnetic measurements show paramagnetic behaviour in the range of 80–300 K. Moreover, the magnetic susceptibility data show a sign of the charge ordering transition about 230 K.

We have investigated the influence of Ca doping on chemical and physical properties of the La2NiO4+δ compounds. Several Ca-doped compounds were then prepared by the citrate method. The X-ray diffraction analysis indicates that all the obtained compounds are pure with no presence of secondary phases. All compounds adopt a tetragonal structure with I4/mmm space group. As x increases, the excess oxygen δ decreases. Magnetic susceptibility shows anomaly below 200 K, which was attributed to charge ordering. Magnetization measurements displayed prominently the presence of weak ferromagnetism below 200 K. Most probably, the ferromagnetic component modifies the antiferromagnetic fluctuations in the NiO2 planes. The origin of the ferromagnetic component must be related to a presence of kind of bond-centered stripes.

Electrical resistivity of La2NiO4+ δ single crystals has been investigated. Results showed several anomalies that are related to the onset of spin and charge ordering, either static or dynamic.

Optical conductivity and electrical resistivity of La2NiO4+δ ( δ = 0.11 and 0.14) single crystals have been investigated for the ( a , b ) plane. Results show several changes of regime that are connected with the onset of spin and charge order, static or dynamic. A surprising contrast of data for both samples, in optical and electrical conductivity, is observed at lowest temperatures. In particular, a pronounced spin glass behavior is observed for δ = 0.11 . In the δ = 0.14 sample, the progressive melting of the charge order scales with the temperature dependence of the oscillator strength of a “forbidden” mode related to folding to the Brillouin zone center of a mode for a wavevector q = ( 0.28 , 0.28 , 0 ) associated with the modulation of stripes.

Optical conductivity spectra of conducting oxides including high-TC cuprates - compared to non-superconducting nickelates in particular - deduced from infrared reflectivity spectroscopy in polarized light and their doping and temperature dependence, are discussed with emphasis on the signatures of intrinsic inhomogeneities of charge carrier concentration. The model of disordered metal is shown to be compatible with the general loss of spectral weight in the optical conductivity upon decreasing frequency, instead of a maximum conductivity at zero frequency as found within a Drude description. In high-TC multilayer cuprates, the discussion focuses upon the c-axis response and the inhomogeneity of the electronic concentration related to the conducting planes alternating with insulating sheets. The onset of stripes that are intrinsic inhomogeneities of the charge carrier distribution is discussed in the example of nickelates.

Structural, electrical and IR reflectivity have been investigated for hole doped Nd 2− x Ca x NiO 4+ δ . X-ray diffraction has shown that the orthorhombic strain decreases when x increases from 0.05 to 0.33; above the strain increases with x . The dc resistivity indicates a semi-conducting behaviour, which can be described using two conduction modes: a variable-range hopping (VRH) mode at low temperature and a thermically activated mode at high temperature. The temperature of change of conduction mode is function of doping rate. Besides, the thermal resistance of Nd 1.67 Ca 0.33 NiO 4 compound presents an incident around 200 K, which is attributed to a charge ordering. IR reflectivity does not show any difference in phonon region. But, it exhibits a Mott-Hubbard gap and a difference on plasma frequency depending on x.

The electrical resistivity of La 2 Ni 1− x Zn x O 4+ δ polycrystalline samples with x varying from 0.1 to 0.5% atom are investigated in relation with the formation and the correlation lengths of charge and spin ordered stripes. It appears almost impossible to explain the activated transport properties by conventional semi-conductor models where the holes are homogeneously distributed in the lattice. Present results rather suggest that the Zn-doping plays an important role on the charge transport and modifies the manner that the holes and spins are arranged in the system.

The electrical resistivity of a single crystal sample of La2NiO4+δ with δ=0.11 is investigated in relation with the formation and correlation lengths of charge and spin ordered stripes. It appears almost impossible to explain the activated transport properties by conventional semi-conductor models where the holes are homogeneously distributed in the lattice. Present results rather suggest that the magnetic fluctuations play an important role on the charge transport and are strongly dependent upon the oxygen content.

A single crystal of La 2 NiO 4+δ with δ=0.11 giving a hole concentration favouring phase separation, has been studied by infrared reflectivity between 4 K and 300 K, from 20 to 7,000 cm -1. The spectra cannot be fitted properly by usual models and both plasma frequency and integrated conductivity shows two anomalies with temperature interpretable in terms of charge and spin ordering and their arrangements into stripes.

Electronic and magnetic peculiarities of La 2 NiO 4+ δ are discussed emphasizing charge and spin ordering phenomena. Macroscopic measurements of conductivity (dc, optical) and magnetic susceptibility on samples of well-known oxygen stoichiometries agree to show anomalies where this peculiar ordering is expected. Our data account for the heterogeneous nature of the magnetism. The susceptibility which is quasi temperature independent in a large T range is modeled by a system of spins cluster.

Magnetic properties of La{sub 2}NiO{sub 4.16} and La{sub 2{minus}x}Pr{sub x}NiO{sub 4+{delta}} are studied by dc susceptibility in a wide temperature range, i.e., 4--1,200 K. The principal aim is to investigate the modifications of magnetic interactions in the NiO{sub 2} plane by inserting a magnetic ion in the LaO layer. Magnetic properties are considerably different with and without praseodymium. When 0 0.5, a single Pr{sup 3+} effect might dominate.

We report an investigation of magnetic resonance by ESR in oxygen-doped La2NiO $$_{4 + \delta }$$ emphasizing extensively for the first time the role of oxygen stoichiometry. The work is performed at room temperature and on powders with $$0.015 \le \delta \le 0.17$$ . At low field an hysteresis is detected between increasing and decreasing fields, it depends upon $$\delta $$ . The resonance lines have characteristic features of ferromagnetic resonance. The intensity ( $$(I{(\Delta {H_{PP}})^2})$$ ) is used as an experimental parameter for investigating the effect of $$\delta $$ . It allows to built a diagram closely connected to the phase diagram $$T - \delta $$ . It suggests a ferromagnetic coupling depending upon $$\delta $$ . When the (average) structure is tetragonal the low intensity is due to a magnetic polaron of low resistivity. In ranges where a phase separation is detected, the ferromagnetic coupling has a structural origin (DM or local anisotropy) with apparently a strong influence on the electrical resistivity.

A complex behaviour of La 2 NiO 4 + δ with oxygen doping has been studied by resistivity, magnetic susceptibility and ESR measurements. Resistivity data have been achieved in the temperature range 4–1000 K with 0 ≤ δ ≤ 0.17: anomalies connected with a phase separation or a new structural order are observed. ESR spectra [95 ≤ T (K) ≤ 300] show a strong change of line shape when δ ≥ 0.11 where stripe order establishes. Comparison of X-band and Q-band suggests the presence of local fields. Below room temperature, the temperature dependence of ESR line for δ = 0.11 may be connected with spin correlation in stripes. The magnetic susceptibility data [300 ≤ T (K) ≤ 1200] show an anomaly at 640 K associated with a disappearance of a ferro-ferrimagnetic contribution the origin of which is associated with hole doping.

Textured YBa2Cu3O72x samples have been studied by electronic paramagnetic resonance. EPR spectroscopy allows us to analyze the Y2BaCuO5 second phase present as inclusions in the YBa2Cu3O6 textured matrix. All samples were deoxygenated in order to limit the skin effect due to conductivity. This is applied to samples textured according to different techniques. Preferential orientation of these particles according to the 123 matrix can be observed. For instance, if texturing under a magnetic field, the particular Y2BaCuO5 orientation is observed of the b211 axis ~b57.132 A! parallel to c123 and to the magnetic field direction. By appropriate calculations from initial spectra, the fraction of preferred orientation of these Y2BaCuO5 grains can be quantified. This orientation comprises 1662 % of the Y2BaCuO5 weight for texturing under a magnetic field, presently one of the highest values obtained. It involves the longest size of Y2BaCuO5 elongated grains lying in YBa2Cu3O6 planes, facilitating the texturation process. Texturing on Y2O3 by the modified melt textured growth method leads to a preferential orientation of Y2BaCuO5 grains too, but in another direction, i.e., b211 perpendicular to c123 . There is no Y2BaCuO5 preferential orientation if texturing with a thermal gradient or on a monocrystalline MgO substrate. This type of analysis can be applied easily to other systems ~nanocomposites, dispersoids, etc.!, providing that the signal of the secondary phase can be clearly separated from the signal of the primary one. @S0163-1829~97!06001-3#

The purpose of this work is to develop a new route for BST synthesis. BST thin film are produced by spin coating on an oriented LNO/Si substrate. The phase purity and possible crystalline orientation are determined by XRD. BST microstructure and texturation are discussed from detailed SEM images and capacitance measurement confirm the BST performances.

Scandium oxides nanopowders have been synthesized using a sol-gel route. ScOOH nanoparticles have been first prepared in solution using ScCl3, xH2O as precursor. Influence of pH and reflux time on particles size and shape has been studied. Sc2O3 nanoparticles were then obtained after ScOOH sol drying. Sols were characterized by laser granulometry, thermogravimetry and differential analysis (TGA- DSC). Depending on pH, 40 to 1000 nm size ScOOH particles can be obtained. At a given pH, the reflux time duration also influences the ScOOH particles size. The ScOOH sol can be used to prepare highly pure Sc2O3 nanopowders. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microcopy (TEM), were used to characterize Sc203 nanopowders obtained from the various ScOOH solutions. The DSC and laser granulometry data indicate a strong relation between the nanoparticles size and the temperature of transformation of g-ScOOH to Sc2O3. Depending on the sol preparation various particles Sc2O3 size can then be obtained allowing the selection of the more suitable powder for transparent ceramic preparation.

In the present study we focused on the nickelate system, which presents stable stripe order and allow a large domain of oxygen doping. More specifically, we studied the non-stoichiometric system La2NiO4 in which the oxygen excess tends to order. ESR technique has been used due to its sensibility to microscopic magnetic fluctuations. We present a systematic study of the charge and spin fluctuations in oxygen doped nickelates to get insight into the dynamic of the system using ESR. The intrinsic resonance signal of polycrystalline La2NiO4 - values 0.09 and 0.12 have been studied, in a large temperature range (10K < T < 300 K). The = 0.12 compound has been chosen as a starting point, since neutron diffraction studies in composition very close to this value have been well characterized the stripe order in this system, showing that the holes order at around TCO = 200K, while the spins order at TS = 110K. By analogy, the ESR results on this compound allowed us to interpret the results in the other compound.

Room temperature ferromagnetism (FM) was observed in laser ablated undoped $\mathrm{Sn}{\mathrm{O}}_{2}$ thin films grown on $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ substrates (the saturated magnetization is about $12\phantom{\rule{0.3em}{0ex}}\mathrm{emu}∕{\mathrm{cm}}^{3}$, as half of that of the $\mathrm{Ti}{\mathrm{O}}_{2}$ films with the same thickness). Experiments on Mn-doped $\mathrm{Sn}{\mathrm{O}}_{2}$ films show that a transition-metal doping does not play any key role in introducing FM in the system. Mn doping (even if with a small content), in fact, just degrades the structure of the $\mathrm{Sn}{\mathrm{O}}_{2}$ host and, as a consequence, reduces its magnetic moment. Both oxygen vacancies and confinement effects are assumed to be key factors in introducing magnetic ordering into $\mathrm{Sn}{\mathrm{O}}_{2}$.

The interaction between an acoustic wave and a complex media has an increase interest for both nondestructive testing (NDT) applications and for biomedical ultrasound. Today, new optimized excitations are generated thanks to the analysis of symmetry properties of the system such as reciprocity, nonlinear time reversal (TR) and other pulse-inverted (PI) techniques. Generalized TR based NEWS (Nonlinear Elastic Wave Spectroscopy) methods and their associate symmetry skeleton will be taken as an example. Among these family of “pulse coded excitation,” solitonic coding constitutes a new scheme in the sense that solitary waves are the best candidates for pulse propagation in nonlinear and layered media, such as tooth or skin. As another application of mixing properties in a wide frequency range, new broadband techniques are needed in the domain of the preservation of cultural heritage. The analysis of the composition of the stones is one of the key parameters in the study of aging historic buildings. The use of TR-NEWS based analysis combined with a FTIR-based system has shown a specific property of the tuffeau limestone where damaged sample contains calcite. In both domains, aging properties of complex medium are extracted thanks to the use of enhanced nonlinear signal processing tools.

Remarkable room-temperature ferromagnetism was observed in undoped $\mathrm{Ti}{\mathrm{O}}_{2}$, $\mathrm{Hf}{\mathrm{O}}_{2}$, and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ thin films. The magnetic moment is rather modest in the case of ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ films on MgO substrates (while on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ substrates, it is negative showing diamagnetism) when the magnetic field was applied parallel to the film plane. In contrast, it is very large in the other two cases (about 20 and $30\phantom{\rule{0.3em}{0ex}}\mathrm{emu}∕{\mathrm{cm}}^{3}$ for $200\text{\ensuremath{-}}\mathrm{nm}$-thick $\mathrm{Ti}{\mathrm{O}}_{2}$ and $\mathrm{Hf}{\mathrm{O}}_{2}$ films, respectively). Since bulk $\mathrm{Ti}{\mathrm{O}}_{2}$, $\mathrm{Hf}{\mathrm{O}}_{2}$, and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ are clearly diamagnetic, and moreover, there are no contaminations in any substrate, we must assume that the thin film form, which might create necessary defects or oxygen vacancies, would be the reason for undoped semiconducting or insulating oxides to become ferromagnetic at room temperature.

The temperature dependence of the infrared reflectivity spectra of a single crystal of ${\mathrm{La}}_{2}{\mathrm{NiO}}_{4+\ensuremath{\delta}},$ with an oxygen excess $\ensuremath{\delta}=0.11,$ is analyzed by both Kramers-Kronig analysis and an attempt to fit with optical conductivity models for the polarization within the basal plane. This oxygen excess corresponds to a composition of the phase diagram where stripe formation has been reported by other methods. In particular, highly anomalous low-frequency tails of incompletely screened phonon responses are suspected to be the signature of static charge stripes, treated here as multipolarons. By comparison with the positions of extra peaks and with the dispersion curve of phonons, a charge-order wave vector Q has been determined. More generally, the analysis allows us to discriminate trapped and mobile charge carriers. A change of regime from mobile to trapped polarons upon cooling is evidenced. Two thresholds in the temperature dependence of relevant parameters and/or data are evidenced for this sample. One is assigned to charge ordering and the other confirms the onset of combined charge and spin order reported at low temperature by other methods.

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Fe-doped HfO2 thin films are room temperature ferromagnetic. In comparison with results of the undoped HfO2 films, it seems that the Fe doping is not the main cause for the ferromagnetism but only acts as a catalyst. Experimental results of oxygen annealing and vacuum heat treatments have proven that in this family of compounds, magnetism might originate from oxygen vacancies or defects. Removing oxygen enhances the magnetic moment, while reversibly filling up oxygen vacancies can destroy the ferromagnetic ordering of the system.

Laser ablated Ni-doped HfO_2 thin films fabricated under a wide range of growth conditions all showed ferromagnetism above room temperature. However, the films deposited at 800 °C under an oxygen partial pressure of 10^ Torr have the largest magnetic moment of 2.7μB/ Ni. Ni-doped HfO_2 films also well demonstrate a large anisotropy. Magnetic force microscopy measurements confirmed that Ni-doped HfO2 films are real room temperature ferromagnets with a domain structure, and that the size of magnetic domains is larger than 10 μm.