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Here, we report a study of white-ochre powders with targeted composition MnWO4 prepared via a coprecipitation method. Through X-ray total scattering combined with pair distribution function analysi...

International audience; Mechanochromic luminescent materials exhibiting emission changes easily detectable by simple means present appealing applicative perspectives for strain detection. Along with design investigations, an in-depth understanding of the mechanochromism mechanism is of utmost importance for guiding the development of such stimuli-responsive devices. In this article, an original luminescent mechanochromic copper iodide cluster and its utilization as an active component for the synthesis of mechanically responsive films are reported. This formulated compound [Cu4I4(PPh(2)i-Pr)(4)] displays a contrasted emission off-on effect upon mechanical solicitations. Structural characterization and spectroscopic analyses supported by theoretical investigations permit to attribute the mechanochromic mechanism to the structural changes of the molecular cluster at the defects created locally in the crystalline structure. The non-classical luminescence behaviour of the pristine crystalline cluster was rationalized by density functional theory calculations demonstrating that the very long Cu-Cu distance destabilizes the emissive triplet state of the classical cluster core. The shortening of these intramolecular Cu-Cu contacts upon mechanical forces permits the recovery of the classical luminescence properties of cubane copper iodide clusters with an intense room temperature emission. Mechanically responsive films based on the studied cluster were prepared by a direct synthesis method within the substrate. These films exhibit high contrasted luminescence mechanochromic properties with writing and erasing activating and deactivating, respectively, the emission of the photoactive component. The mechanochromic phenomenon was distinctly followed by scanning electron microscopy.

Manganese oxides based materials, as γ-MnO2/“Ag2O”, are considered to control the hydrogen risk from radioactive waste packaging. The efficiency of hydrogen trapping at room temperature has been demonstrated. However, in accidental conditions, the increasing temperature can be detrimental for hydrogen performance in nuclear waste packages. As a function of temperature, structural evolution of γ-MnO2/“Ag2O” getter was determined by X-Ray Diffraction (XRD), Pair Distribution Function (PDF) and Thermogravimetric Analysis (TGA). Kinetics of the hydrogen trapping were related to the structure evolution of γ-MnO2/“Ag2O”. Ramsdellite (R-MnO2) and pyrolusite (β-MnO2) were the main phases existing below 400 °C, then Ag-hollandite (quadratic), Ag-hollandite (monoclinic), Mn2O3 and Mn3O4 were formed at 500 °C, 600 °C, 700 °C and 850 °C, respectively. Hydrogen trapping was efficient until 400 °C where the γ-MnO2 structure remains.

Polarized Raman measurements were recorded on a monoclinic brushite (CaHPO4.2H2O) crystal in the 800–1200 cm−1 spectral range, corresponding to the PO stretching modes. This study is a continuation of the investigation of the phosphate stretching modes observed in polarized infrared reflectance spectra of brushite crystal. In such ionic non-centrosymmetric crystals, the splitting between the transverse and longitudinal components of the optic vibrations was observed in the polarized Raman spectra recorded at several scattering geometries. A″ symmetry modes of the brushite crystal were measured. Using a simple model based on the symmetry of the PO4 group, the Raman intensities of the stretching modes are calculated and compared with experimental bands. Copyright © 2016 John Wiley & Sons, Ltd.

The assembly of two distinct organic photochromic groups and polyoxometalate (POM) within a single molecule has been realized. In the hetero-functionalized Anderson polyanion MnMo6O18(SP)(SN), one spiropyran and one spironaphthoxazine cap the two faces of a planar {MnIIIMo6VIO18} fragment. A related symmetrical POM where the {MnIIIMo6VIO18} inorganic moiety is connected to two spironaphthoxazines has also been obtained, and isolated as an organoammonium (MnMo6O18(SN)2) or a cationic spiropyran ((SP)3MnMo6O18(SN)2) salt. The structures of MnMo6O18(SN)2 and MnMo6O18(SP)(SN) have been solved by single-crystal X-ray diffraction analysis. In solution, both compounds exhibit electrochromic properties with multiple redox coloured states. The solid-state photochromism of all the compounds has also been extensively studied at room temperature. Contrary to the organic spironaphtoxazine derivative SNTris which is very poorly photochromic, the pale yellow colour of MnMo6O18(SN)2 shifts to deep blue with high coloration contrast which underlines the positive effect of the grafting onto the inorganic platform. In addition, MnMo6O18(SN)2 also shows good cyclability and exhibits a fast bleaching process. Finally, the temperature dependence of the solid-state photochromic properties of MnMo6O18(SN)2 is also reported and compared to that of the related MnMo6O18(SP)2. The photo-coloration process which is attenuated at low temperatures in both cases is clearly more affected for MnMo6O18(SN)2. Moreover, the thermal fading process becomes significant at 340 K for MnMo6O18(SP)2 and 260 K for MnMo6O18(SN)2 underlining strong different optical behaviours between both materials.

International audience; The first systems associating in a single molecule polyoxotungstates (POTs) and photochromic organic groups have been elaborated. Using the (TBA)4[PW11O39{Sn(C6H4I)}] precursor, two hybrid organic-inorganic species where a spiropyran derivative (SP) has been covalently grafted onto a {PW11Sn} fragment via a Sonogashira coupling have been successfully obtained. Alternatively, a complex containing a silicotungstate {PW11Si2} unit connected to two spiropyran entities has been characterized. The purity of these species has been assessed using several techniques, including 1H and 31P NMR spectroscopy, mass spectrometry, and electrochemical measurements. The optical properties of the hybrid materials have been investigated both in solution and in the solid state. These studies reveal that the grafting of SPs onto POTs does not significantly alter the photochromic behavior of the organic chromophore in solution. In contrast, these novel hybrid SP-POT materials display highly effective solid-state photochromism from neutral SP molecules initially nonphotochromic in the crystalline state. The photoresponses of the SP-POT systems in the solid state strongly depend on the nature and the number of grafted SP groups.

Ultrathin Ag2Mo3O10·2H2O nanowires (NWs) were synthesized by soft chemistry under atmospheric pressure from a hybrid organic-inorganic polyoxometalate (CH3NH3)2[Mo7O22] and characterized by powder X-ray diffraction, DSC/TGA analyses, FT-IR and FT-Raman spectroscopies, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Their diameters are a few tens of nanometers and hence much thinner than that found for silver molybdates commonly obtained under hydrothermal conditions. The optical properties of Ag2Mo3O10·2H2O NWs before and after UV irradiation were investigated by UV-vis-NIR diffuse reflectance spectroscopy revealing, in addition to photoreduction of Mo(6+) to Mo(5+) cations, in situ photogeneration of well-dispersed silver Ag(0) nanoparticles on the surface of the NWs. The resulting Ag@Ag2Mo3O10·2H2O heterostructure was confirmed by electron energy-loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and Auger spectroscopy. Concomitant reduction of Mo(6+) and Ag(+) cations under UV excitation was discussed on the basis of electronic band structure calculations. The Ag@Ag2Mo3O10·2H2O nanocomposite is an efficient visible-light-driven plasmonic photocatalyst for degradation of Rhodamine B dye in aqueous solution.

BaSF was synthesised by a solid state reaction at high temperature and its crystal structure was determined thanks to X-ray diffraction on a single crystal. This transparent yellow fluorochalcogenide has an intergrowth structure built from the stacking of fluorite type layers and sulfur layers. In BaSF sulfur atoms form dimers with interatomic distances as short as 2.1074(10) A. DFT calculations confirm that this compound is a band insulator with the Fermi level lying in between the antibonding π* and σ* molecular orbitals of the sulfur dimers. Reflectance measurements show that the optical band gap of BaSF is about 2.7 eV in good agreement with the value found from DFT calculations.

International audience; A series of compounds of Co(1-x)Mg(x)MoO(4) compositions has been prepared by a conventional ceramic route. The members of the whole solid solution exhibit a reversible first-order phase transition which was probed by using thermal expansion and low-temperature reflectivity techniques. Whereas the α → β transition temperature evolves linearly on warming from 435 to 200 °C with x going from 0 to 0.9, the β → α transition temperature variation falls down on cooling from -40 °C to -140 °C going from CoMoO(4) to Co(0.1)Mg(0.9)MoO(4) with an asymptotic evolution. The phase transition temperatures have been explained on the basis of a crystal polarization effect under substitution of Mg for Co. Thus, from an applicative point of view, new thermochromic pigments with tunable transition temperatures are here proposed.

The precipitation of rare earth phosphates (RE = La, Ce, Pr, Nd, and Lu), from RECl3 was investigated in molten LiCl–KCl eutectic at 500 °C in air. Ammonium dihydrogenphosphate (NH4H2PO4) was used as the phosphorus precursor. X-ray diffraction analysis indicated the formation of compounds with monazite (La, Ce, Pr, and Nd) or xenotime (Lu) structures. 31P NMR spectroscopy measurements confirmed that lanthanum formed pure monazite, which indicates a LaCl3 → LaPO4 conversion factor near 100%. These results demonstrate that the stoichiometric addition of NH4H2PO4 is sufficient to obtain quantitative precipitation at 500 °C of anhydrous rare earth phosphates in molten LiCl–KCl. The use of this type of precursor, which has the advantage of not modifying the chemical composition of the medium after recovery of the rare earth phosphates, could be considered during the first step of purification of chlorinated baths containing fission products arising from spent fuel reprocessing by a pyrochemical process.

The fluorescence and phosphorescence properties of Europium-doped M Al 2 Si 2 O 8 ( M =Ca, Sr, Ba) are reinvestigated and discussed on the basis of the propensity of an activator to agglomerate with an oxygen vacancy. Due to a stronger attraction of the anion vacancy towards Eu 2+ cations going from BaAl 2 Si 2 O 8 to SrAl 2 Si 2 O 8 and CaAl 2 Si 2 O 8 host lattices, the interpretation of the fluorescence spectra turns out to be less trivial in the Ca and Sr host lattices than in the Ba one and requests the account for Eu 2+ cations lying at alkaline-earth sites with or without vacancy in their neighborhood. Phosphorescence in these compounds is highlighted.

The infrared and Raman spectra of Na substituted β-TCP are presented for various levels of substitution. The influence of Na content on main vibrational modes appears significant and among them the ν1 symmetric stretching band is very sensitive to PO4 3- tetrahedrons environment. Thus, this mode was particularly investigated and has been decomposed using Lorentzian shapes components. We assigned the calculated components to the different types of PO4 3- tetrahedrons present in the crystalline structure.

The members of the CuMo1 - xWxO4 series (0 ≤ x < 0.1) undergo a first-order phase transition at normal pressure, which can be induced by temperature. The two allotropic forms exhibit two distinguishable colors, green for the high-temperature form (α) and brownish-red for the low temperature one (γ), which opens up a new market for user-friendly temperature indicators. From X-ray diffraction and microprobe analyses as from optical properties, the tungsten substitution rate for molybdenum is limited to 12%. Beyond, a third, parasitic wolframite-type phase, CuMo0.6W0.4O6, systematically crystallizes besides the α/γCuMo0.9W0.1O4 compounds. Within the CuMo1 - xWxO4 solid-solution domain, the dependence of the transition temperatures was followed by calorimetry, optical reflectivity, and magnetism. On the basis of these measurements, the transition is characterized for all of the chemical compositions by a hysteresis loop of about 90 K in width with a temperature transition strongly dependent on the tungsten co...

Intensive researches on specific treatments of radioactive cesium, occurring in high level nuclear wastes, are in progress in France. Nowadays, a cesium immobilization in host matrices with a high chemical durability seems to be the favourite option. In that perspective, titanium based upon hollandite is a good candidate as a host matrix because of its high cesium incorporation ability, its excellent chemical stability, and its capacity to support charge compensation during the Cs+ into Ba2+ transmutation process. In this study we report the preparation and crystal growth in a BaF2—B2O3 flux melt of the Ba x Cs y M z Ti8–z O16 hollandite phase and its characterization by single crystal X-ray diffraction. An attention was focused on materials with M = Al or Al + Fe and with barium only since single crystals including cesium could not be obtained from the flux method. An incommensurate modulation of the Ba cation site occupancy, with I4/m(00γ)00 as a superspace group, was observed for all the single crystals under study.

International audience; The hollandite Ba1Cs0.28Fe0.82Al1.46Ti5.72O16, which has been proposed for the cesium-specific conditioning, can be synthesized either by an alcoxyde or a dry route. In both cases, a two-step protocol is applied, i.e., a calcination at 1000 1C followed by a sintering at 1200 1C. After sintering, both synthetic processes lead to a tetragonal form. According to the X-ray diffraction (XRD) patterns collected at the barium and the cesium K absorption edges, the different positions of these two elements have been evidenced with a more centered position in the oxygen cubic site of the tunnel for Ba than for Cs. On the contrary, after calcination, the two synthetic routes yield different products. The alcoxyde route gives rise to a mixture of the aforementioned Cs- and Ba-containing tetragonal I4/m hollandite, a Cs-only-containing monoclinic I2/m hollandite and an unidentified phase with a weak coherence length containing only Ba. The dry route yields a single tetragonal hollandite material containing Ba and Cs slightly different in composition from the targeted compound.

Bi2O2(OH)(NO3) is the first bismuth oxynitrate containing [Bi2O2]2+ layers for which the crystal structure has been determined. The current study presents its synthesis, formula determination using powder XRD, thermogravimetric analysis and nitrate assay, and finally, crystal structure refinement from twinned crystals. Bi2O2(OH)(NO3) crystallizes in the orthorhombic system, a = 5.3878(11), b = 5.3984(10) and c = 17.136(2) Å , with the space group Cmc21. The structure refinement based on 1257 independent reflections converged to RI (obs) = 0.0321 and RIw (obs) = 0.0765. The Bi2O2(OH)(NO3) structure is based on [Bi2O2]2+ sheets in the (ab) plane. The interlayer space is composed of two slices containing OH− and (NO3)− groups, respectively. Within the nitrate layers, the disorder over two possible NO3- orientations (related by a four fold axis) involves half occupied positions for two of the oxygen atoms. An attempt to lower the symmetry and/or enlarge the unit cell, looking for an (NO3)− ordering, failed

In the presence of "Ag2O" as a promoter, γ-MnO2 traps dihydrogen in its (2 × 1) and (1 × 1) tunnels. The course of this reaction was examined by analyzing the X-ray diffraction patterns of the HxMnO2/"Ag2O" system (0 ≤ x < 1) on the basis of pair distribution function and density functional theory (DFT) analyses. Hydrogen trapping occurs preferentially in the (2 × 1) tunnels of γ-MnO2, which is then followed by that in the (1 × 1) tunnels. Our DFT analysis shows that this process is thermodynamically favorable.

For the very first time, sulfonium polyoxometalate (POM) assemblies are shown to develop efficient solid-state photochromism in ambient conditions. The optical properties of the already known Rb(0.75)(NH(4))(5.25)[(Mo(3)O(8))(2)O(O(3)PC(CH(2)S(CH(3))(2))OPO(3))(2)]·8H(2)O (1) and a new material (Me(3)S)(4)[Mo(8)O(26)] (2) under UV excitation are investigated by diffuse reflectance spectroscopy, revealing that the color change effect is highly tunable playing with the nature of the POM. A mechanism involving the photoreduction of Mo(6+) cations associated with electron transfers from the sulfonium cations toward the POMs is proposed.

International audience; Polarized infrared (IR)reflectancemeasure ments at near-normal incidence were recorded from the ac-plane of amonoclinic brushite (CaHPO4 2H2O)crystal in the 800-1200cm 1spectral range (P-Ostretch- ing modes).The adjustment of these data,on the basis of adispersion analysis (DA)model for monoclinic case,allowed the determination of oscillators parameters for the four P-Ostretching observed modes of the phosphate group.

We investigate the influence of MnO 2 polymorphism form on MnO 2 /Ag 2 O hydrogen getter. The results show that the performances strongly depend on the polymorphism form of manganese oxide. The nsutite γ-MnO 2 phase, which consists of a random intergrowth of MnO 2 –ramsdellite and MnO 2 –pyrolusite building blocks, shows the more promising performances to trap H 2 via the formation of hydroxyl groups. This observation is especially relevant for compounds with a low pyrolusite/ramsdellite ratio and a high rate of microtwinnings.

International audience; Light harvesting chalcogenide materials have strong potential applications for photovoltaic due, in part, to the ability of their structures to accommodate shift from the ideal stoichiometry. This study is devoted to the chemical and structural investigations of two specific series of materials, Cu(In, Ga)Se2 (CIGSe) and Cu2ZnSnS4 (CZTS). Both of them receive currently a strong incentive in the domain of thin film solar cells. On the basis of accurate chemical analyses, conventional powder and single-crystal X-ray diffraction, resonant X-ray scattering with synchrotron radiation the capacity of the chalcopyrite and kesterite structures of CIGSe and CZTS to accommodate deviations from the stoichiometry is discussed. Formally, the former is found to be more flexible than the latter even if this one can self adapt to copper-poor and copper-rich compositions without any structural change except in terms of the cation distributions.

International audience; Two new hybrid organic-inorganic molybdates based on layered (2/∞)[Mo(n)O(3n+1)](2-) blocks and organoammonium cations (+)(Me(x)H(3-x)N)(CH(2))(6)(NH(3-x)Me(x))(+) (x = 0-1), namely, (H(3)N(CH(2))(6)NH(3))[Mo(7)O(22)]*H(2)O (1) and (MeH(2)N(CH(2))(6)NH(2)Me)[Mo(9)O(28)] (2), have been synthesized under hydrothermal conditions. The (2/∞)[Mo(9)O(28)](2-) unit in 2 is an unprecedented member of the (2/∞)[Mo(n)O(3n+1)](2-) family with the n value extended to 9. The structural filiation between the (2/∞)[Mo(n)O(3n+1)](2-) (n = 5, 7, 9) blocks is well established, and their structural similarity with the (2/∞)[MoO(3)] slabs in α-MoO(3) is also discussed. Single-crystal X-ray analyses show that the (2/∞)[Mo(n)O(3n+1)](2-) layers in 1 and 2 are pillared in the three-dimensional networks by the organic cations with a similar connection at the organic-inorganic interface. In addition, a correlation between the topology of the (2/∞)[Mo(n)O(3n+1)](2-) blocks in 1 and 2 and the overall sizes of the associated organic cations is pointed out. Finally, the efficiency of Fourier transform Raman spectroscopy to easily discriminate the different (2/∞)[Mo(n)O(3n+1)](2-) blocks (n = 5, 7, 9) in hybrid organic-inorganic layered molybdate materials is clearly evidenced.

Seven hybrid organic-inorganic bisphosphonate molybdenum(VI) polyoxometalate complexes with the general formula [(Mo(3)O(8))(4)(O(3)PC(C(m)H(2m)NRR'R″)(O)PO(3))(4)](8-) (m = 3; R, R', and R″ = H or CH(3)) and [(Mo(3)O(8))(2)(O)(O(3)PC(C(m)H(2m)NRR'R″)(O)PO(3))(2)](6-) (m = 3 or 4; R, R', and R″ = H or CH(3)) have been synthesized and their structures solved using single-crystal X-ray diffraction. These compounds are made of a {Mo(12)} or a {Mo(6)} inorganic core functionalized by various alkylammonium bisphosphonates, with these ligands differing by the length of their alkyl chains and the number of methyl groups grafted on the N atom. The nature of the counter-cations (Na(+), K(+), Rb(+), Cs(+), and/or NH(4)(+)) constituting these materials has also been modulated. (31)P NMR spectroscopic studies in aqueous media have shown that all the dodecanuclear complexes reported here are stable in solution, whereas for the hexanuclear compounds, a dynamic equilibrium between two isomers has been evidenced, and the corresponding standard thermodynamic parameters determined for one of them. The electrochemical properties of six representative compounds of this family have been investigated. It has been found that the Mo(6+)/Mo(5+) reduction potential is similar for all the polyoxometalates studied. Besides, it is shown that electrochemical cycling is an efficient method for the deposition of these compounds on a surface. The photochromic properties of all the complexes reported herein have been studied in the solid state. Under irradiation in the near ultraviolet (UV), the {Mo(12)} systems shift from white to reddish-brown, while the {Mo(6)} compounds develop a purple coloration. The coloration kinetics has been systematically quantified and the optical band gaps, the salient coloration kinetic parameters and the coloration kinetic half-life times have been determined. This has evidenced that several of these materials develop very strong and rapid UV-induced color changes, with remarkable coloration contrasts. Finally, the optical properties of these systems are discussed in light of several salient parameters as the POM topology, the nature of the grafted bisphosphonate ligand, and the design of the hydrogen-bonding network at the organic-inorganic interface.

Addition of a gallium (Ga) precursor in the typical reaction protocols used for the preparation of β-tricalcium phosphate (β-TCP) led to novel Ga-doped β-TCP ceramics with rhombohedral structures (R3c space group). From the refinement of their X-ray diffraction patterns, it was found that the incorporation of Ga in the β-TCP network occurs by substitution of one of the five calcium (Ca) sites, while occupation of another Ca site decreases in inverse proportion to the Ga content in the structure. The Ga local environment and the modification of the phosphorus environments due to the Ga/Ca substitution in Ga-doped β-TCP compounds are probed using (31)P and (71)Ga magic-angle spinning NMR. A decrease of the unit cell volume is observed with increasing Ga content, together with improved mechanical properties. Indeed, the compressive strength of these new bioceramics is enhanced in direct proportion of the Ga content, up to a 2.6-fold increase as compared to pure β-TCP.

International audience; A new concept of photoresponsive composites has been elaborated by intimately connecting a Photochromic Phase (PP), (H(2)DABCO)(2)(HDMA)(0.5)Na(0.75)(H(3)O)(0.75)[Mo(8)O(27)]*3H(2)O (1), with a second hybrid organic-inorganic molybdate material, (H(2)DABCO)(HDABCO)[Fe(OH)(6)Mo(6)O(18)]*4H(2)O (2) acting as an Oxidation Catalytic Phase (OCP) toward the former once photoexcited. The association of both the PP and the OCP in the composite drastically improves the bleaching process of the PP alone because of efficient electronic transfers through the OCP-PP interface without affecting significantly its photoinduced color change characteristic. Two OCP-PP composites with different PP weight percents have been obtained by associating 1 with 2. The optical properties of these composites before and after UV irradiation have been investigated by Diffuse Reflectance Spectroscopy, and the strong impact of the OCP on the fading kinetics of the PP has been clearly highlighted.

International audience; In this paper, we report X-ray diffraction investigations as well as Raman and solid-state (31)P and (23)Na magic angle spinning nuclear magnetic resonance (NMR) characterization of three series of calcium orthophosphates. The general formulae of the studied compounds are Ca(10.5-x/2)M(x)(PO(4))(7), where M=K or Na and x=0, 0.25, 0.50, 0.75, 1.0; and Ca(10)K(x)Na(1-x)(PO(4))(7), where x=0, 0.25, 0.5, 0.75, 1.0. These calcium orthophosphates are found to be isostructural with β-tricalcium phosphate (β-TCP, Ca(3)(PO(4))(2)) with the substitution of some calcium sites by potassium and/or sodium cations. The unit cell parameters vary continuously with the level of substitution, a characteristic of these solid solutions. The Raman spectra show the different vibrational bands of the phosphate groups PO(4), while the NMR chemical shifts are sensitive to the non-equivalent phosphorus and sodium ions present in these substituted samples. As both Raman and NMR spectroscopies are local probes, they offer tools to distinguish between these different phosphorus and phosphate groups, according to their structural site and local environment, especially the type of cation substituent. A convenient decomposition of the Raman and NMR spectra into Gaussian-Lorentzian components leads us to propose an assignment of the main observed bands of these substituted β-TCPs.

International audience; The presence of alkylammonium groups covalently grafted on bisphosphonato ligands induces photochromic properties to ligand-coordinated polyoxomolybdate systems. Such intrinsically photoactive polyanions can be used for the preparation of materials combining photochromic polyoxometalates and functional countercations.

The thermoluminescence (TL) properties of the Eu 2+ doped Ba 13− x Al 22−2 x Si 10+2 x O 66 ( x ∼ 0.6) phosphorescent materials (hereafter labeled BASO:Eu) are analyzed on the basis of the thermally connected traps (TCT) model. Basically, in these materials, Eu 2+ cations are photo-ionized under UV excitation, and electrons are trapped at defects. The return to the ground state is thermo-stimulated, and the freed electrons recombine at photo-oxidized activator sites with emission of light. TL properties between 80 and 650 K, as well as an isothermal emission decay (IED) at room temperature, were collected for BASO:Eu1% and BASO:Eu0.5% samples to characterize the phosphorescence mechanism in this series of materials and to determine the trap depths. Thermoluminescence glow curves of BASO:Eu excited either at 254 nm or at 365 nm, or excited at 254 nm for durations of 10 s and 240 s, as well as the IED, agree well with a TCT model. Based on our analysis, phosphorescence in BASO:Eu compounds is associated with the depletion of five traps with depths of 0.56, 0.61, 0.65, 0.69 and 0.73 eV.

International audience; We investigate the reactivity of MoO(4)(2-) toward six organoammonium cations (+)(Me(3-x)H(x)N)(CH(2))(2)(NH(y)Me(3-y))(+) (x, y = 1-3) at different synthesis temperatures ranging from 70 to 180 °C. A total of 16 hybrid organic-inorganic materials have been synthesized at an initial pH of 2, via ambient pressure and hydrothermal routes, namely, (H(2)en)[Mo(3)O(10)]*H(2)O (1), (H(2)en)[Mo(3)O(10)] (2), (H(2)en)[Mo(5)O(16)] (3), (H(2)MED)(2)[Mo(8)O(26)]*2H(2)O (4), (H(2)MED)[Mo(5)O(16)] (5), (N,N-H(2)DMED)(2)[Mo(8)O(26)]*2H(2)O (6), (N,N-H(2)DMED)(2)[Mo(8)O(26)]*2H(2)O (7), (N,N'-H(2)DMED)(2)[Mo(8)O(26)] (8), (N,N'-H(2)DMED)[Mo(5)O(16)] (9), (H(2)TriMED)(2)[Mo(8)O(26)]*4H(2)O (10), (H(2)TriMED)(2)[Mo(8)O(26)]*2H(2)O (11), (H(2)TriMED)[Mo(7)O(22)] (12), (H(2)TMED)(2)[Mo(8)O(26)]*2H(2)O (13), (H(2)TMED)(2)[Mo(8)O(26)] (14), (H(2)TMED)(2)[Mo(8)O(26)] (15), and (H(2)TMED)[Mo(7)O(22)] (16). All of these compounds contain different polyoxomolybdate (Mo-POM) blocks, i.e., discrete β-[Mo(8)O(26)](4-) blocks in 6, 10, 13, 14, (1)/(∞)[Mo(3)O(10)](2-), and (1)/(∞)[Mo(8)O(26)](4-) polymeric chains in 1, 2, 4, 7, 8, and 15, respectively, and (2)/(∞)[Mo(5)O(16)](2-) and (2)/(∞)[Mo(7)O(22)](2-) layers in 3, 5, 9, 12, and 16, respectively. The structures of 5, 9, and 14 have been resolved by single-crystal X-ray analyses. The characterization of the different Mo-POM blocks in 1-16 by Fourier transform Raman spectroscopy is reported. The impact of the synthesis temperature on both the composition and topology of the Mo-POM blocks is highlighted.

International audience; First principles density functional calculations were carried out for model compounds Ba12EuAl22Si10O66 and Sr12EuAl22Si10O66 to account for the luminescence properties of Eu2+ doped Ba13_xAl22_2xSi10+2xO66 and Eu2+ doped (Ba,Sr)13_xAl22_2xSi10+2xO66. Both host lattices have three different crystallographic alkaline earth sites, namely, AE(1), AE(2) and AE(3), at which the dopants Eu2+ are located. The fluorescence properties of Eu2+ doped Ba13_xAl22_2xSi10+2xO66 are not explained if the dopant ions Eu2+ are considered to randomly occupy the three different Ba sites, but are explained if the dopants are considered to preferentially occupy the Ba(3) sites. In contrast, the fluorescence properties of Eu2+ doped (Ba,Sr)13_xAl22_2xSi10+2xO66 are explained only when both Sr2+ and Eu2+ cations are considered to occupy the AE(3) sites, which suggests that the activators are more randomly distributed over the three AE sites in Eu2+ doped (Ba,Sr)13_xAl22_2xSi10+2xO66 than in Eu2+ doped Ba13_xAl22_2xSi10+2xO66. Calculations evidence the strong tendency for the Ba(3) sites to accommodate defects in Ba13_xAl22_2xSi10+2xO66, namely, Eu dopants, Sr substituents, and Ba vacancies. This arises from the higher malleability of the Ba(3) site compared to the Ba(1) and Ba(2) sites.

The synthesis of lanthanum phosphates in molten LiCl-KCL eutectic was chosen to address the preliminary treatment of chlorinated wastes containing fission products that are already present in a Li/Cl eutectic. The obtained monazite compound shows interesting properties to be considered as a good candidate to trap lanthanum for a long-time. The synthesis route based on LaCl(3) reaction with NH(4)H(2)PO(4) in a stoichiometric amount is a key point to obtain monazite as a pure phase. Hence, the salt composition is not modified during the synthesis reaction. The chemical reactivity of ammonium dihydrogenphosphate (NH(4)H(2)PO(4), hereafter abbreviated ADP) toward lanthanum chloride (LaCl(3)) in molten LiCl-KCl eutectic is probed by NMR spectroscopy to follow the formation of LaPO(4). Formally, a direct transformation of the two aforementioned precursors into LaPO(4), NH(4)Cl and HCl can be discarded on the basis of the low thermal stability of ADP. To shed some light on the formation of LaPO(4), in situ and ex situ NMR experiments were carried out on LiCl-KCl/LaCl(3)/ADP, as well as LiCl-KCl/ADP, KCl/ADP, and LiCl/ADP mixtures. First, the reactivity of the precursors in contact with the eutectic was studied from room temperature to 600 degrees C by means of (31)P, (35)Cl, and (139)La high temperature NMR. Second, ex situ room temperature magic angle spinning (MAS) and RadioFrequency driven recoupling (RFDR) (31)P solid-state NMR experiments were carried out on solid samples prepared in different conditions (i.e., temperature and atmosphere) and quenched at room temperature to identify frozen intermediate species in their metastable state. On the basis of this approach, we propose a model for the LaPO(4) formation based on a multistep mechanism which highlights the strong reactivity of ADP toward the alkaline salts but without final change in the composition of the solvent.

International audience; The members of the CuMo1−xWxO4 series (0 ≤ x < 0.1) undergo a first-order phase transition that can be induced by pressure application; the thermochromic properties of such a series have already been reported. The two polymorphic forms exhibit two distinguishable colors: green for the low pressure form (α) and brownish-red for the high pressure one (γ). These oxides can open up a new market for friendly pressure indicators, particularly for the compositions (0.07 ≤ x ≤ 0.1) for which the two polymorphs are stable at room temperature, that is, for which the color transition via pressure application is nonreversible. Within the CuMo1−xWxO4 solid solution domain, the dependence of the transition pressure versus tungsten content, temperature of measurement, and sample thermal-pressure history was studied. A large control of the transition pressure (from 5 to several 100 MPa) was brought to the fore. The transition was then studied using X-ray diffraction and transmission electron microscopy-energy dispersive X-ray analyses. This first-order transition, occurring by atomic migration inside the cell, seems to be preceded by an atomic disordering; moreover, transition temperatures may be modified by W segregation at the surface of the grains.

International audience; The optical properties of Eu-activated (Ba,Sr)13−xAl22−2xSi10+2xO66 materials have been determined after the structural reinvestigation of the hypothetical Ba13Al22Si10O66 material on the basis of the Gebert's model. The white fluorescence and phosphorescence of the (Ba,Sr)13−xAl22−2xSi10+2xO66:Eu series result from the existence of two broad emission bands associated with 8H-4f65d1 → 8S-4f7 transitions peaking at 534 and 438 nm, the intensities of which may be tuned at room temperature via the control of the europium concentration and the substitution of Sr for Ba. This suggests the possibility to adjust the emission of the material to white LED requisites.

International audience; A thermochromic substance changes its color when subjected to a temperature variation in a certain range. For practical reasons, the thermochromism should occur in the temperature range appropriate for desired applications. CuMoO4 exhibits thermochromism1–3 in the temperature region between ~175 and ~260 K, which depends strongly on the heating/cooling rate, and has two polymorphs, that is, the high temperature (HT) form (i.e., α form) and the low temperature (LT) form (i.e., γ form). The temperature-induced color change in CuMoO4 originates from a first order phase transition between the two structures (with ~10% shrinking of the unit cell volume at the transition).4 A recent study of tungsten-doped derivatives of CuMoO4, that is, CuMo1–xWxO4 (x < 0.12), showed that the temperature range of their thermochromism can be raised to a more easily accessible range.5, 6 These materials are thus attractive for uses around room temperature. For example, at ambient pressure, CuMo0.9W0.1O4 changes its color from red to green by warming above ~360 K and from green to red by cooling below ~275 K. Furthermore, the color change from green to red can be triggered by applying a weak pressure (e.g., finger push; Figure S1 of the Supporting Information), and the green color is regained by heating.5, 6 The α- and γ-type structures of CuMoO4 are maintained in the CuMo1–xWxO4 (x < 0.12) solid solution. It is of interest to probe how well CuMoO4 and its tungsten derivatives can withstand repeated cooling/warming (C/W) cycles without losing their thermochromism significantly. In the present work we examine this question of cyclability by performing optical absorbance (OA) at 520 nm, differential scanning calorimetry (DSC) analyses, and magnetic susceptibility measurements as well as spin dimer analysis for the α and γ structures of CuMoO4. Our study reveals that, after a number of repeated cooling/warming cycles, the α-form loses its ability to transform into the γ-form. The structural and physical properties of CuMo1–xWxO4 (x < 0.12) are not reported here because of their strong similarities to those of CuMoO4. Figure 1 shows how the OA value at 520 nm of CuMoO4 varies during the C/W cycles between 10 and 300 K with C/W rate of 1.5 K·min–1 (see Figure S2 of the Supporting Information for measurements with a 5 K·min–1 C/W rate). At high temperature, the single phase material is green so that the light of wavelength 520 nm is reflected hence falling down the OA values. When the temperature is lowered, the green to red transition occurs. Thus, the reflectivity spectrum changes with absorption ranging approximately from orange to UV, and the OA value increases.5, 6 To a first approximation, the OA value at 520 nm reflects the relative percentage of the α and γ forms in the probed sample. Once the α → γ transition is initiated by cooling, the α form can be recovered by warming. However, at the second cooling, only a part of the α form changes to the γ form. With increasing the number of C/W cycles, the amount of the α form that changes to the γ form decreases progressively so that the hysteresis loop of the OA versus T plot progressively becomes smoothed out, and finally the α form is stabilized in a wider temperature range. Experiments carried out with different C/W rates lead to the same observations except that, at a lower C/W rate, the total disappearance of the γ-form requires more C/W cycles without change in the transition temperatures.

The discrimination between atomic species in light-element materials is a challenging question. An archetypal example is the resolution of the Al/Si ordering in aluminosilicates. Only an average long-range order can be deduced from powder X-ray or neutron diffraction, while magic-angle-spinning NMR provides an accurate picture of the short-range order. The long- and short-range orders thus obtained usually differ, hence raising the question of whether the difference between local and extended orders is intrinsic or caused by the difficulty of obtaining an accurate picture of the long-range order from diffraction techniques. In this communication we resolve this question for the monoclinic phases of BaAl2Si2O8 and SrAl2Si2O8 on the basis of 27Al NMR measurements and ab initio simulation of electric field gradient. Although the long- and short-range orders deduced from our XRD and NMR experiments differ, they become similar when the XRD atomic positions are optimized by ab initio electronic structure calculations.

X-ray patterns of the Ba{sub 1}Cs{sub 0.28}Fe{sub 0.82}Al{sub 1.46}Ti{sub 5.72}O{sub 16} compound evidence two wide peaks at low angle in addition to the well defined peaks of the I4/m hollandite structure type. Two hypotheses have been explored to account for these features: the coexistence of the hollandite phase with an amorphous phase and the appearance of a commensurate or incommensurate modulated structure associated with a cationic ordering, as proposed in the literature. Actually, even if the amorphous phase quantification by the Rietveld method reveals about 15 wt% of non-crystalline phase in some of the powdered sample, the origin of the two wide peaks was found to stem from the incommensurate modulated character of the hollandite structure type (super space group I4/m(0 0 {gamma})0 0) with a distribution of the modulation wavevectors presumably related to slight chemical composition changes. - Graphical abstract: Amorphous phase localization.

International audience; The mechanism of phosphorescence in SrAl2O4:Eu,Dy material is discussed on the basis of a thermo-activated release of electrons trapped at oxygen vacancy sites. The depths and concentration of the electron traps are strongly affected by codoping with trivalent lanthanide cations Ln3+. This finding is rationalized by comparing the ionization potentials of the dopant cation Eu2+, the codopant cation Ln3+ and the substituted cation Sr2+. Such a use of ionization potentials provides a practical guide with which the variation of the phosphorescent decay time in the codoped derivatives of SrAl2O4:Eu is predicted.

International audience; Without presuming the reversible or irreversible character of the phenomenon, X-chromic materials may be defined as compounds whose color changes under an external stimulus...

International audience; The phosphorescence mechanisms of various phosphors were explored by taking into consideration the presence of interactions between dopant cations and vacancies as well as the effect of co-dopant cations on these interactions. Our study indicates that the distribution of dopant and co-dopant cations around vacancies is not random, and luminescent properties are strongly influenced by this nonrandom distribution. To a first approximation, the ionization potentials of dopants, co-dopants, and host cations can be used to rationalize their tendencies for this nonrandom distribution. On the basis of our analysis, we explained the properties of known phosphorescent materials, examined several factors important for designing new improved phosphors, and discussed how point defects might affect phosphorescence as well as fluorescence

For the preparation of beta-TCP and biphasic calcium phosphates (BCPs, mixtures of hydroxyapatite and beta-TCP), the presence of sodium in the reaction medium results in the incorporation of sodium in the beta-TCP network, by substitution of some calcium sites. Accordingly, a decrease of the unit cell volume of -TCP was observed with increasing sodium substitution. The distribution of sodium in the beta-TCP structure, as a function of the amount incorporated, was probed using 31P and 23Na MAS NMR and 31P{23Na} REDOR experiments. It was shown that an estimation of the sodium content in beta-TCPs could be obtained from the modeling of their 31P MAS NMR spectra. Moreover, the incorporation of sodium in beta-TCPs results in improved mechanical properties, without affecting the biocompatibility of the ceramics.

International audience; The existing mechanisms proposed to explain the phosphorescence of SrAl2O4:Eu2+,Dy3+ and related phosphors were found to be inconsistent with a number of important experimental and theoretical observations. We formulated a new mechanism of phosphorescence on the basis of the facts that the d orbitals of Eu2+ are located near the conduction band bottom of SrAl2O4, that the Eu2+ concentration decreases during UV excitation, and that trace amounts of Eu3+ are always present in these phosphors. In our mechanism, some Eu2+ ions are oxidized to Eu3+ under UV, and the released electrons are trapped at the oxygen vacancy levels located in the vicinity of the photogenerated Eu3+ cations. The phosphorescence arises from the recombination of these trapped electrons around the photogenerated Eu3+ sites with emission at 520 nm. The codopant Dy3+ enhances the phosphorescence by increasing the number and the depth of electron traps, and the codopant B3+ enhances the phosphorescence by increasing the depth of electron traps. We also probed the origin of another emission at 450 nm of SrAl2O4:Eu2+ that occurs at low temperatures. Our analysis indicates that this emission is caused by a charge transfer from oxygen to Eu3+ cations and is associated with a hole trapping.

Bi 2 O 2 (OH)(NO 3 ) is the first bismuth oxynitrate containing [Bi 2 O 2 ] 2 + layers for which the crystal structure has been determined. The current study presents its synthesis, formula determination using powder XRD, thermogravimetric analysis and nitrate assay, and finally, crystal structure refinement from twinned crystals. Bi 2 O 2 (OH)(NO 3 ) crystallizes in the orthorhombic system, a = 5.3878(11), b = 5.3984(10) and c = 17.136(2) A, with the space group Cmc2 1 . The structure refinement based on 1257 independent reflections converged to R I (obs) = 0.0321 and R I w (obs) = 0.0765. The Bi 2 O 2 (OH)(NO 3 ) structure is based on [Bi 2 O 2 ] 2 + sheets in the (ab) plane. The interlayer space is composed of two slices containing OH- and (NO 3 ) - groups, respectively. Within the nitrate layers, the disorder over two possible NO 3 - orientations (related by a four fold axis) involves half occupied positions for two of the oxygen atoms. An attempt to lower the symmetry and/or enlarge the unit cell, looking for an (NO 3 ) - ordering, failed.

In the quest of a new material for high potential electrochemical cycling (about 5 V vs. Li + /Li), we have studied the LiMPO 4 /Li systems with M=Mn, Fe, Co and Ni. To explain the wide average potential range in the series (4, 3.5, 4.8 V, respectively, and probably much higher for Ni), a DFT calculation was done, tacking into account a possible spin-polarization effect. The obtained results rule out any possible bi-electronic process for the highest potentials, as proposed in the literature. Some first electrochemical results are given for LiCoPO 4 , its voltage vs. Li being reasonable from the point of view of high potential electrolyte stability. In optimized conditions, a reproducible electrochemical capacity of 110 mAh/g could be reached during the first discharge.

Single-walled carbon nanotubes (SWNTs) offer the prospect of both new fundamental science and useful (nano)technological applications1. High yields (70–90%) of SWNTs close-packed in bundles can be produced by laser ablation of carbon targets2. The electric-arc technique used to generate fullerenes and multi-walled nanotubes is cheaper and easier to implement, but previously has led to only low yields of SWNTs3,4. Here we show that this technique can generate large quantities of SWNTs with similar characteristics to those obtained by laser ablation. This suggests that the (still unknown) growth mechanism for SWNTs must be independent of the details of the technique used to make them. The ready availability of large amounts of SWNTs, meanwhile, should make them much more accessible for further study.

International audience; Polyoxometalates covalently linked to one or two spiropyran entities have been isolated. These organic-inorganic hybrids exhibit multi-electrochromic and photochromic properties.

Delafossite CuGaO2 is a prototype p-type transparent semiconducting oxide. We report here a new ethylene glycol (EG) mediated hydrothermal synthesis route to this material from soluble hydrated metal nitrates. We found that EG acts as a reducing agent which eases the formation of CuGaO2 by stabilizing Cu(I) at low temperature in hydrothermal conditions. Moreover, we observed that the initial pH of the precursors solution is a key parameter to tune the particle sizes (from 2 µm to 300 nm) and subsequently the color (from dark brown to light gray) of the CuGaO2 powder. The optimal synthesis conditions to obtain the brightest product are described. In these conditions, the CuGaO2 powder exhibits a pale grayish color and contains 300 nm large nano-layered particles approximately 20 nm thick.