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Microstructured orthovanadate BaCo3(VO4)2(OH)2 has been prepared by hydrothermal treatment of pyrovanadate Co3V2O7(OH)2·2H2O. The impact of crystallite size on the structural and magnetic properties have been discussed.

New anhydrous alkali lanthanide-free polyoxometalates have been elaborated by thermal decomposition of their parent hydrates, and they exhibit remarkable reversible turn-off-on luminescence properties at room temperature in the presence of humidity.

International audience; Two new cubic perovskite oxides Ba3CoSb2O9 and Ba2SrCoSb2O9 were prepared and characterized. Ba3CoSb2O9 was prepared in polycrystalline form by high-pressure (HP) high-temperature treatment of the hexagonal 6H polytype of Ba3CoSb2O9. Polycrystalline samples of Ba2SrCoSb2O9 were obtained at ambient pressure by a solidstate reaction method. Combined Rietveld refinements of X-ray and neutron diffraction patterns indicated that HP Ba3CoSb2O9 and Ba2SrCoSb2O9 both crystallize in a Fm (3) over barm cubic double perovskite A(2)BB'O-6 structure with formulae Ba-2(Sb0.83Co0.17)(Co0.5Sb0.5)O-6 and (Ba1.33Sr0.67)Sb(Co0.7Sb0.3)O-6, respectively. Electron diffraction results obtained for Ba2SrCoSb2O9 showed no sign of additional periodicity. Weiss temperatures extracted from high-temperature magnetic susceptibility data were. theta approximate to -113 K and -118 K for HP Ba3CoSb2O9 and Ba2SrCoSb2O9, respectively. HP Ba3CoSb2O9 displays a weak ZFC-FC magnetic irreversibilty below 8 K. Ba2SrCoSb2O9 exhibits a spin freezing at T-f approximate to 6 K, and mu SR and Sb-121 NMR data revealed a magnetic transition towards a disordered ground state.

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.

Solubility equilibria of solids in water are an integral part of the thermodynamic assessment of the long term behavior of nuclear waste in geological formations. In this paper, we do not provide new thermodynamic data on solubility of relevant solids but we show, under which conditions meaningful thermodynamic data can be derived from solubility data and under which conditions this is not the case. Application of isotopic exchange techniques shows that sometimes equilibrium is only established between the surface and the solution, in other cases equilibrium involves the overall solid/liquid phase system. In case of slow reaction rates of oxides of tetravalent radionuclides, bulk phase thermodynamic data cannot be obtained from such systems.

Here, we report a study of white-ochre powders with targeted composition MnWO

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.

We show that the type-II multiferroic properties of bulk MnWO4 are kept in nanostructured ceramics of 50 nm grain size prepared via spark plasma sintering (SPS). This means that ferroelectric polarization is robust against downsizing, which is at variance with standard ferroelectrics like BaTiO3. We ascribe this stability to the spin-driven nature of the ferroe-lectric correlations in type-II multiferroics while it is resulting from lattice distortion in other cases. This may open the way for persistent type-II multiferroicity with no need for external stabilization like substrate-generated strain.

γ-MnO2is a material formed by random intergrowth of two phases, β-MnO2andR-MnO2. It is demonstrated here on seven γ-MnO2samples that pair distribution function analysis using a conventional X-ray diffraction setup (Bragg–Brentano geometry with a molybdenum anode) allows the quantification of this intergrowth simplyviaa simulation of the actual material by a mixture of β-MnO2andR-MnO2phases. Although this method does not take into account specifically the relaxed distances in the vicinity of the intergrowth zone, it is found to be very robust, accurate and in full agreement with the widely used quantification based on the empirical approach of Chabre & Pannetier [Prog. Solid State Chem.(1995),23, 1–130].

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; The influence of magnetic field on the dielectric properties of several Mn1-x(Mg,Zn)xWO4 multiferroic ceramics is investigated, and confirms an additional phase transition below the ferroelectric Curie temperature previously detected in this system in zero magnetic field. In highly doped samples an original plateau of the capacitance is observed between T2 and this additional transition. Pyroelectric measurements in zero magnetic field for a Mn0.85Mg0.15WO4 ceramic confirm the existence of this unexpected low temperature phase transition. The magnetic or structural origin of this transition is discussed.

A novel gallium-doped -tricalcium phosphate (-TCP) ceramics with rhombohedral structure (R3c space group) can be obtained by the addition of a Ga precursor in the typical reaction protocols used for the preparation of -TCP. It was found, from the refinement of their XRD patterns, that the incorporation of Ga in the -TCP network occurs by substitution of one of the five calcium sites, while occupation of another Ca site decreases in inverse proportion to the gallium content in the structure. A decrease of the unit cell volume is observed with increasing gallium 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 -TCP.

Several substituted â-tricalcium phosphates have been prepared with different cations (monovalent, divalent and trivalent) and at various levels of substitution. Structural investigations have proved that fewer than ~10% wt substitution, the substituted compounds are isostructural to â- TCP, leading to solid solutions. These samples have been characterized by infrared and Raman spectroscopies. The vibrational spectra show mainly the bands related to the vibrations of PO43- tetrahedrons present in the structure. As Raman scattering and infrared absorption are local probes, the bands are sensitive to the local environment of the distinct tetrahedrons, related to the site of substitution and to the nature of the cations.

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.

Technetium is a long-lived product of nuclear fission which commonly exhibits two oxidation states (IV and VII). Siderite (FeCO3), suspected to be formed as a container corrosion product in geological radioactive waste repositories, may concentrate by coprecipitation more than 90% of technetium-99, present as Tc(IV) in surrounding aqueous fluids. X-ray diffraction and transmission electron microscopy measurements indicate that technetium can be incorporated within the siderite structure, even if we note that technetium-bearing green rust phase may also be observed. These results suggest that siderite might play a beneficial role in limiting Tc diffusion to the next environment of nuclear waste repositories.

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.

Owing to its high technological importance for optoelectronics, zinc oxide received much attention. In particular, the role of defects on its physical properties has been extensively studied as well as their thermodynamical stability. In particular, a large concentration of Zn vacancies in ZnO bulk materials is so far considered highly unstable. Here we report that the thermal decomposition of zinc peroxide produces wurtzite-type ZnO nanoparticles with an extraordinary large amount of zinc vacancies (>15%). These Zn vacancies segregate at the surface of the nanoparticles, as confirmed by ab initio calculations, to form a pseudo core-shell structure made of a dense ZnO sphere coated by a Zn free oxo-hydroxide mono layer. In others terms, oxygen terminated surfaces are privileged over zinc-terminated surfaces for passivation reasons what accounts for the Zn off-stoichiometry observed in ultra-fine powdered samples. Such Zn-deficient Zn1-xO nanoparticles exhibit an unprecedented photoluminescence signature suggesting that the core-shell-like edifice drastically influences the electronic structure of ZnO. This nanostructuration could be at the origin of the recent stabilisation of p-type charge carriers in nitrogen-doped ZnO nanoparticles.

This study aims to show the stability of γ-MnO 2 /Ag 2 O hydrogen getter under gamma irradiation in order to be suitable for decreasing the hydrogen risk during the nuclear waste transportation. The chemical and the structural properties of the getter were barely unchanged for irradiated doses up to 4 MGy. The pair distribution function (PDF) analysis showed that the γ-MnO 2 , which can be describe as an intergrowth of the ramsdellite phase (R-MnO 2 ) and the pyrolusite phase (β-MnO 2 ), had the same intergrowth rate (around 60% for β-MnO 2 and 40% for R-MnO 2 ) after irradiation and the silver containing promoter was also unchanged. The getter remains therefore efficient for hydrogen trapping. Furthermore, γ-MnO 2 /Ag 2 O was tested in a closed environment in the presence of hydrogen released by organic technological waste radiolysis, such as polyvinyl chloride, ion exchange resins, polyethylene and silicone. Over 80% of the hydrogen, generated by organic radiolysis, was trapped under a 1.5 MGy gamma irradiation.

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.

High-pressure X-ray diffraction measurements were carried out for polymeric CdI2-type compounds MTe2 (M=Pt, Pd) to investigate if they undergo a structural phase transition under pressure as does IrTe2. Up to 27 GPa at room temperature PtTe2 does not undergo any structural phase transition. In contrast, however, an abrupt change in the inter-atomic distances occurs in PdTe2 above 15.7 GPa at room temperature, and above 5 GPa at 300 °C, but the volume vs. pressure curve exhibits no discontinuity. To account for the differences between the isostructural compounds PtTe2, PdTe2 and IrTe2, their electronic structures and bonding were analyzed on the basis of first principles electronic band structure calculations.

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

Various compositions of solid solutions K{sub 3}P(Mo{sub 1-x}W{sub x}){sub 12}O{sub 40} (0=

A new glass formulation, a calcium and zirconium-enriched alumino-boro-silicate matrix, able to incorporate 12 wt% of molybdenum oxide has been developed in order to trap molybdenum as CaMoO4, a stable phase in a vitreous medium. Laboratory studies on this matrix have shown the impact of the glass thermal treatment on its microstructure. Thus, four cooling rates and heat treatments presented in this paper were investigated to determine if Ca and Mo totally reacted to give CaMoO4 and to localize the powellite phase in the different glasses. Using X-ray diffraction and Rietveld refinements, we were able to quantify both crystallized and amorphous CaMoO4 in all the samples. EDS analyses allowed us to localize it in the glass microstructure. Then coupling together the micrograph analysis and the X-ray diffraction results proved the presence of amorphous powellite and showed its place in the glasses.

The cerium borates o -CeBO 3 , m -CeBO 3 and CeB 3 O 6 have been shown to be isostructural to their lanthanum derivatives. From diffuse reflectance, electron energy loss spectroscopy (EELS) and band structure calculations, it has been evidenced that a Ce 3+ 4 f –5 d transition is responsible for weak absorption peaks around 3.5 eV while the O2 p –Ce5 d charge transfer gives rise to a strong absorption around 7 eV. Starting from self-consistent full potential LAPW calculations, the dielectric tensors of the three compounds were computed and compared to experimental data. It results in a satisfactory fit between the observed and the calculated extinction coefficient k and the index of refraction n .

The bismuth basic nitrate [Bi6O4.5(OH)3.5]2(NO3)11 crystallizes in the monoclinic space group P21 with a=15.850(3) A , b=14.986(3) A , c=18.230(4) A , β=107.329(17)° and V=4133.7(14) A 3 (Z=4) . Its structure has been determined from 120 K , twinned crystal X-ray data (16 781 reflections, 683 parameters, R=0.0703). It is built upon [Bi6Ox(OH)8−x](10−x)+, x=4 and x=5 hexanuclear complexes and nitrate groups. The polycationic entities are linked to the nitrate anions either by hydrogen bonds or through bismuth–oxygen coordination. Even at 120 K , the [Bi6O4(OH)4]6+ and [Bi6O5(OH)3]5+ polycations could not be observed as such, the crystal structure refinement only detecting an average [Bi6O4.5(OH)3.5]5.5+ polycation. To prove the presence of both hexanuclear complexes in the structure, we report the existence of a correlation between the bismuth-linked oxygen bond-valence parameters and the presence, or not, of hydroxyl groups. Moreover, the Raman spectrum of the new anhydrous bismuth basic nitrate is compared to those of [Bi6O5(OH)3](NO3)5·3H2O, [Bi6O4(OH)4](NO3)6·4H2O, and two yet uncharacterized bismuth nitrates.

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.

The compounds Y3Fe5O12 and Y3Fe5-xCrxO12 are synthesized by solid state reaction of stoichiometric mixtures of Y2O3, Fe2O3, and Cr2O3 (air, 1350 °C, 6 h).

Two new photochromic hybrid organic–inorganic supramolecular materials (SN)2[W6O19] (SN2W6) and (SP)2[W6O19]·0.5CH3CN (SP2W6) have been elaborated by combining for the very first time an isopolyoxotungstate [W6O19]2− with both photoswitchable cationic spirooxazine (SN) and spiropyran (SP), via electrostatic interactions. (SN)2[Mo6O19] (SN2Mo6), a third new photochromic compound which contains the [Mo6O19]2− unit, has been also designed. Their structure was solved by single-crystal X-ray diffraction analysis, and their solid-state photochromic properties in ambient conditions were thoroughly investigated by UV-visible diffuse reflectance spectroscopy. SN2W6 and SN2Mo6 have been proved to be isostructural while SP2W6 is isostructural with its already reported counterpart SP2Mo6. In the SN2M6 and SP2M6 series, the SN and SP molecules are in very close contact with the POM units, which a priori should dramatically limit their photoisomerization in the solid state. However, this strongly varies with the nature of the metal in the [M6O19]2− unit. Indeed SN2W6 and SP2W6 exhibit remarkable photochromism under low-power UV excitation (λex = 365 nm) while SN2Mo6 and SP2Mo6 develop very limited color-change effects under similar UV exposure. These results have unambiguously highlighted that the efficiency of the SN and SP photoisomerizations in these hybrid systems is much more impacted by an electronic factor resulting from the intrinsic optical absorption properties of both SP and POM components than by a steric factor induced by crystal packing.

International audience; Polycrystalline samples of Mn1-xCuxWO4 (x ≤ 0.5) have been prepared by a solid-state synthesis as well as from a citrate synthesis at moderate temperature (850 °C). The goal is to study changes in the structural, magnetic, and dielectric properties of magnetoelectric type-II multiferroic MnWO4 caused by replacing Jahn-Teller-inactive Mn(2+) (d(5), S = 5/2) ions with Jahn-Teller-active Cu(2+) (d(9), S = 1/2) ions. Combination of techniques including scanning electron microscopy, powder X-ray and neutron diffraction, and Raman spectroscopy demonstrates that the polycrystalline samples with low copper content 0 ≤ x ≤ 0.25 are solid solution that forms in the monoclinic P2/c space group. Rietveld analyses indicate that Cu atoms substitutes for Mn atoms at the Mn crystallographic site of the MnWO4 structure and suggest random distributions of Jahn-Teller-distorted CuO6 octahedra in the solid solution. Magnetic susceptibility reveals that only 5% of Cu substitution suppresses the nonpolar collinear AF1 antiferromagnetic structure observed in pure MnWO4. Type-II multiferroicity survives a weak Cu substitution rate (x < 0.15). Multiferroic transition temperature and Néel temperature increase as the amount of Cu increases. New trends in some of the magnetic properties and in dielectric behaviors are observed for x = 0.20 and 0.25. Careful analysis of the magnetic susceptibility reveals that the incorporation of Cu into MnWO4 strengthens the overall antiferromagnetic interaction and reduces the magnetic frustration.

ωLi/V 2 O 5 spirally wound polymer (POE) batteries functioning at 90 °C presented an important capacity fading ca. 20th cycle. This behavior could arise from the cathode material itself, including its in situ formation during the first reduction step from αLi/V 2 O 5 , or from a technical problem linked either to the composite cathode or one of the other cell components. In this paper, after rejection of the two first hypothesis, we clearly demonstrate the negative role of the nickel foil used as cathodic collector.

Polycrystalline yttrium iron garnet (Y3Fe5O12, hereafter labeled YIG) has been synthesized by solid-state reaction, characterized by X-ray diffraction, Mössbauer spectroscopy, and UV-vis-NIR diffuse reflectance spectroscopy, and its optical properties from room temperature (RT) to 300 °C are discussed. Namely, its greenish color at RT is assigned to an O(2-) → Fe(3+) ligand-to-metal charge transfer at 2.57 eV coupled with d-d transitions peaking at 1.35 and 2.04 eV. When the temperature is raised, YIG displays a marked thermochromic effect; i.e., the color changes continuously from greenish to brownish, which offers opportunities for potential application as a temperature indicator for everyday uses. The origin of the observed thermochromism is assigned to a gradual red shift of the ligand-to-metal charge transfer with temperature while the positioning in energy of the d-d transitions is almost unaltered. Attempts to achieve more saturated colors via doping (e.g., Al(3+), Ga(3+), Mn(3+), ...) remained unsuccessful except for chromium. Indeed, Y3Fe5O12:Cr samples exhibit at RT the same color than the undoped garnet at 200 °C. The introduction of Cr(3+) ions strongly impacts the color of the Y3Fe5O12 parent either by an inductive effect or, more probably, by a direct effect on the electronic structure of the undoped material with formation of a midgap state.

The Rietveld method has proved to be a very effective means to characterize and quantify the crystalline phases and the amorphous phase in glass ceramic materials using X-ray powder diffraction data. The technique was applied to a borosilicate glass of the type used for high-level nuclear-waste containment, in order to measure the proportions of the crystallized phases after heat treatment and, thus, to qualify the thermal stability of the glass. Six crystalline phases were analysed in this way in an almost entirely (>95 wt%) amorphous material after adding a known proportion of an internal standard (TiO2). The quantitative analyses were corrected to allow for microabsorption effects resulting from grain-size and absorption-contrast effects. In addition to the quantitative data, unit-cell parameters and site-occupancy refinements revealed solid-solution and substitution phenomena in the crystal.

The cerium and potassium thiosilicate KCeSiS 4 has been synthesized at 800 °C from Ce, Si, K 2 S and S precursors weighted in the K:Ce:Si:S = 1:1:1.15:4.3 ratio. This yellow, air stable compound crystallizes in the monoclinic space group P2 1 , (No. 4) with the cell parameters: a = 6.5201(3) A, b = 6.5982(3) A, c = 8.6920(5) A, β = 107.701(3) °, V = 356.23(3) A 3 and Z = 2. Refinement of 36 parameters by the Rietveld method, using 974 reflections led to R p (%) = 2.49, R wp (%) = 3.35 and χ 2 = 2.71. KCeSiS 4 , isostructural to KLnMQ 4 (Ln = La, Nd, Gd, Y; M = Si, Ge; Q= S, Se), consists of two-dimensional ∞ 2 [CeSiS 4 ] − anionic layers separated by K + ions. These layers are built upon [CeS 7 ] distorted monocapped trigonal prisms, sharing 2 edges and 2 corners with each other, and upon [SiS 4 ] tetrahedra linked to the ∞ 2 [CeS 4 ] 5− skeleton by edge and face sharing. From magnetic measurements, an effective magnetic moment μ eff (300 K) = 2.73(2) μ B was calculated in good agreement with the k (i) Ce (III) Si (IV) S 4 (−II) charge balance. From diffuse reflectance measurements, a band gap of 2.68(1) eV correlated to the occurrence of a 4 f → 5 d electronic transition was evidenced. Moreover, chromatic L/a/b coefficients, equal respectively to 88.37/−18.85/52.91, have been determined for the bright yellow colour of the compound. These parameters compare rather well with those of NiTiO 3 , a well known industrial pigment. The room temperature strong green luminescence at E = 2.45 eV( λ = 506.1 nm) of KCeSiS 4 has been investigated through emission and excitation spectroscopy in the UV-visible range.

The cathodic materials r-Li 0.8 H 0.2 FeO 2 (ramsdellite-type) and o-Li 0.7 H 0.3 FeO 2 (orthorhombic form) were synthesized in an autoclave by reaction of iron oxohydroxides with lithium ethoxide in anhydrous ethanol. The compositions of the phases were determined both by means of elemental analyses and density measurements. The crystal structures of r-Li 0.8 H 0.2 FeO 2 and o-Li 0.7 H 0.3 FeO 2 were determined by the Rietveld method. The powders were made of homogeneously distributed submicronic needles. Electrochemical tests of the Li 1–x H x FeO 2 /Li systems were carried out along with X-ray diffraction and Mossbauer spectroscopy. The results from all the physical techniques employed taken together showed the instability of Fe 4+ formed during the recharge of the Li 1–x H x FeO 2 materials, forbidding cycling on the Fe 4+ /Fe 3+ electrochemical couple.

The assisted photochemical conversion of precursor polymer synthesized via the procedure using tetrahydrothiophenium group is studied, particularly the influence of the substrate temperature and duration of the illumination period followed by optical absorption measurements The optimal experimental conditions are obtained for a substrate temperature T = 110°C a`nd an illumination period of at least 30 min. The characterization of the optimized photochemically converted poly( p -phenylene vinylene) [PPV] has been investigated by means of optical absorption, infrared absorption, X-ray diffraction and resonant Raman scattering spectroscopy. We find that optical and structural properties of the optimized photoconverted are rather close to those of standard PPV

Two lithium iron oxides r-Li0.8H0.2FeO2 (ramsdellite-type) and o-Li0.7H0.3FeO2 (orthorhombic structure) have been synthesised by an ion exchange reaction between respectively α-FeOOH and γ-FeOOH, and C2H5OLi at 170 °C and 140 °C. The reaction products were characterised through elemental analyses, infrared spectroscopy, density measurements and X-ray diffraction. The refinement of the powder XRD patterns of r-Li0.8H0.2FeO2 and o-Li0.7H0.3FeO2 has been performed by the Rietveld method and the results show that the products are isostructural to their precursors.