There have been substantial scientific works in the past years for finding adequate immobilization matrices for iodine radioisotopes. Lately, iodosodalite glass-ceramics or glass-composites represent a promising material. Under pressure, glass-ceramics represent an even better material. In the present work, we have synthesised I-bearing glass-ceramics under low pressure conditions (0.5 GPa) and using a thermal step from melting (1250 degrees C) to crystallization temperature (813 degrees C). The produced materials show the coexistence between I-rich iodosodalite (>10 mol. % I) and I-poor glass matrix (<1 mol. % I) and without the presence of detrimental crystalline phase such as nepheline. The iodosodalite proportion remains low though (similar to 10 %). Raman spectroscopy on the iodosodalite crystals seems to indicate that the beta cage could be filled either with I- or IO3- species. The analyses of the glass structure using B-11 NMR show an increase in the BO4 proportion that could suggest an increase in the chemical durability. In the end, the produced materials have most of the prerequisite for a relevant matrix for immobilization of iodine radioisotopes.

LAS glass-ceramics stimulate considerable attention in academic and industrial fields due to exceptional properties, such as low thermal expansion coefficient, transparency or superior mechanical strength. We report here an experimental investigation of LAS structure and microstructure using conventional techniques as XRD or S/TEM, but also an innovative technique based on electron diffraction mapping. The later gives a topography of the sample and a clear picture of the distribution between the glass and the spodumene particles. All the data converge towards a model of hard spheres where 75% of the volume is composed of spheroid particles and 25% of the remaining volume is composed of glass, which is present in the inter-particle interstices. These findings provide a new knowledge about the LAS system and may offer useful guidance for other researchers in ceramic community.

The impact of dehydration/rehydration processes on the luminescence properties of the Na7[SbW6O24]·nH2O (n = 0, 4, 10, 16) lanthanide-free polyoxometalates is reported. Na7[SbW6O24] is a new turn-off luminescence sensor for detecting humidity.

Using jointly experimental results and first-principles calculations, we unambiguously assign the underlying mechanisms behind two commonly observed luminescence bands for the Al2O3 material. Indeed, we show that the red band is associated with a Ti(3+)d-d transition as expected, while the blue band is the combination of the Ti3+ + O- -> Ti4+ + O2- and V-O(center dot)+e(-) -> V-O(x) de-excitation processes. Thanks to our recent developments, which take into account the vibrational contributions to the electronic transitions in solids, we were able to simulate the luminescence spectra for the different signatures. The excellent agreement with the experiment demonstrates that it should be possible to predict the color of the material with a CIE chromaticity diagram. We also anticipated the luminescence signature of Al2O3:Ti,Ca and Al2O3:Ti,Be that were confirmed by experiment.

Dense ceramic samples of wolframite-type MnMoO4 (w-MnMoO4) have been prepared by Cool-SPS (Spark Plasma Sintering) for the first time with the goal of investigating the magnetic, dielectric, and magneto-electric properties of this thermally fragile polymorph of MnMoO4. Earlier studies found that w-MnMoO4 converts to the structurally different alpha-MnMoO4 phase if heated in air at 873 K, thus hindering fabrication of w-MnMoO4 ceramics by conventional high-temperature sintering. Unsintered powder samples, which were prepared via a hydrothermal method, and dense ceramics elaborated by Cool-SPS have the same magnetic properties. Magnetic susceptibilities display Curie-Weiss behaviour, chi = C/(T-theta), with effective moments for Mn2+ ion mu(eff) approximate to 5.9 mu(B)/Mn-atom and negative Weiss temperatures theta approximate to - 96 to - 98 K. Unlike the isostructural multiferroic compounds MnW1-xMoxO4 (0 <= x < 0.3) which exhibits at least two successive magnetic transitions below 15 K, w-MnMoO4 undergoes only one paramagnetic-to-antiferromagnetic transition at T-N approximate to 32 K. The field-dependent magnetization at 2 K shows a spin-flop transition at mu H-0(SF) approximate to 2 T. Capacitance and dielectric losses obtained for a ceramic between 2 and 300 K in zero field and in a field of 9 T reveal several weak anomalies. Dielectric anomalies are observed at the magnetic phase transition, suggesting a magnetoelectric coupling. Qualitatively different dielectric and magnetodielectric behaviours occur in alpha-MnMoO4 ceramics at low temperature.

Intercalation/deintercalation reactions enable introduction/removal of intercalants without destructive structure transformation of host lattices. They are among the most versatile ways to design metastable phases attainable in mild synthesis conditions. Recently, topochemical deintercalation of oxygen anions has opened up an avenue to access new compounds with unusual transition metal oxidation states and interesting properties. So far, the scope of such anion deintercalation was mainly restricted to oxides and their oxyhalide derivatives. However, lately, we presented a proof-of-concept study on the sulfur deintercalation reaction driven by anionic redox in La2O2S2. Here, we extend this work and present the design of new members of a family of slightly colored non-centrosymmetric metastable oxysulfides. Our work shows that the reduction with an alkali metal of sulfur dimers in Ln(2)O(2)S(2) (Ln = Pr, Nd) precursors leads to the topochemical deinsertion of half of the sulfur atoms of each S-2 pair, producing two new metastable oA-Ln(2)O(2)S (Ln = Pr, Nd) phases. The non-centrosymmetric compounds oA-Ln(2)O(2)S (Ln = La, Pr, Nd) evidence second and third harmonic generation effects, suggesting the potential applicability of the topochemical route for design of nonlinear optical materials.

Microplatelets of the layered-kagome compound BaCo3(VO4)2(OH)2, which is the Co2+ analogue of mineral vesignieite BaCu3(VO4)2(OH)2, have been prepared with very high yield by hydrothermal reaction using synthetic karpenkoite Co3V2O7(OH)2·2H2O as starting reagent. The Rietveld refinement of X-ray diffraction data indicates that Co3V2O7(OH)2·2H2O is isostructural with martyite Zn3V2O7(OH)2·2H2O. Two single-phased samples of microstructured BaCo3(VO4)2(OH)2 have been characterized using powder X-ray diffraction, FT-IR and Raman spectroscopies, thermal analyses, scanning electron microscopy, energy-dispersive X-ray spectroscopy and magnetisation measurements. Their crystallite sizes perpendicular to the c-axis are in the range of 92(3) to 146(6) nm and depend on the synthesis conditions. Results have been compared to those previously obtained for quasi-spherical nanoparticles having a crystallite size of the order of 20 nm, to explore the effect of the crystallite size on the properties of BaCo3(VO4)2(OH)2. This study highlights that the magnetic properties depend on the crystallite sizes only at low temperatures.

La2O2S2 was recently used as a precursor to prepare either a new metastable form of La2O2S by de-insertion of half of sulfur atoms of (S2) dimers or quaternary compounds by insertion of a coinage metal (e.g., La2O2Cu2S2). A strong structural relationship exists between the polysulfide precursor and the synthesized products, which highlights the topochemical nature of these reactions. Nevertheless, the crystal structure of the precursor material is still a matter of debate. Namely, several structural models were reported so far in the literature with different space groups and/or crystal systems. All these models were built upon infinite [Ln2O2] slabs separated from each other by a flat sulfur layer of (S2) dumbbells. Nevertheless, all (S2) dimers within a given sulfur layer may rotate in phase by 90° compared to the ideal model that induces an overall atomic disorder in (S2) dimer orientation along the stacking axis. This leads to some imbroglio and much confusion in the description of structural arrangement of Ln2O2S2 materials. Herein, the crystal structures of La2O2S2 and its Pr and Nd variants are revisited. We propose an alternative model that reconciles pre-existing structural descriptions of Ln2O2S2 (Ln = La, Pr, and Nd) materials and highlights the strong dependency of the degree of long-range ordering of the sulfur layers on the synthesis conditions.

Pure micro- and nanocrystalline powders of the layered-kagome zinc orthovanadate BaZn3(VO4)2(OH)2 have been successfully prepared and thoroughly characterised. Microstructured samples (BaZn3-MPs) have been produced by hydrothermal reaction using synthetic martyite Zn3V2O7(OH)2·2H2O as the starting reagent. Nanoparticles (NPs) with an average size of ≈ 60 nm (BaZn3-NPs-7h) or ≈ 50 nm (BaZn3-NPs-25min) have been obtained by using a coprecipitation method at ambient pressure, and by varying the stirring time. Rietveld refinements of X-ray diffraction data indicate that micro- and nanostructured BaZn3(VO4)2(OH)2 both crystallize in a R3̄m structure very similar to that of the known layered-kagome compound BaCo3(VO4)2(OH)2. Transmission electron microscopy observation of BaZn3-NPs-7h and BaZn3-NPs-25min reveals crystallized NPs with homogenous distributions of Ba, Zn, and V elements. FT-IR and Raman spectra show subtle differences between micro- and nanostructured samples which cannot be linked to any differences in the average crystal structures. The high resolution 51V MAS NMR spectrum of BaZn3-MPs shows a single isotropic line attributed to VO43- groups with C3v point group. The spectra of the nanostructured samples reveal the presence of a weak additional signal which decreases in intensity with increasing the NPs size, and which has been tentatively assigned to the presence at the surface of the NPs of a small amount of V5+ ions in a different chemical environment. Nanostructuring also impacts the optical properties of BaZn3(VO4)2(OH)2. The UV-vis absorption spectra of NPs exhibit an additional weak transition in the visible domain which is not observed for the microstructured sample.

Several matrix types have been considered for the immobilization of iodine radioisotopes from which glass-ceramics represent a serious candidate; however, I-bearing glass-ceramics are challenging owing to the iodine volatility. We have synthesised glass-ceramics from the partial crystallization of a parental glass enriched with different iodine sources (I-2 and I2O5) under high-pressure conditions (up to 1.5 GPa). The samples were characterized using Scanning and Transmission Electron Microscopy and X-ray Diffraction. Using standard synthesis protocol: melting, nucleation and crystal growth, we have obtained glass-ceramics showing the coexistence between I-bearing glass (<0.8 mol.% I), nepheline (NaAlSiO4) and iodosodalite (Na8Al6Si6O24I2 with up to 14 mol.% I). For several samples, we observed also the presence NaPt3O4 witnessing a chemical reaction between the container walls and the inside experimental charge. The structure of iodosodalite is entirely resolved by Rietveld refinement of the XRD pattern for I-2 experiments whereas it cannot be solved for I2O5 experiments suggesting a change in the iodosodalite structure probably due to the beta cage filling by IO3- clusters instead of I-. Our present work could represent a potential solution to tackle the problem of iodine radioisotopes immobilization.

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.

Highly crystalline nanoparticles of BaCo3(VO4)2(OH)2 have been prepared via a new soft-chemistry route, allowing an initial magnetic study of this high-spin d7 layered-kagome compound, which is the Co2+ analogue of the copper mineral vesignieite.

The effects of chemical pressure on the structural and magnetic properties of the triple perovskite Ba3NiSb2O9 are investigated by substituting Sr2+ ions for Ba2+ ions. Two Ba(3-x)SrxNiSb(2)O(9) phases could be stabilized via a solid-state reaction at ambient pressure (AP) in air. The 6H with Sb2O9 pairs (x = 0) -> 6H with NiSbO9 pairs (x = 0.5) -> 3C (cubic with corner-sharing octahedral, x = 1.25) sequence of structural phases occurs with increasing Sr content, i.e., chemical pressure, which is like that previously reported for pure samples of Ba3NiSb2O9 obtained under increasing high physical pressure (HP). For the 6H Ba2.5Sr0.5NiSb2O9 (x = 0.5) phase, using combined Rietveld refinements of powder x-ray and neutron diffraction patterns, precession electron diffraction tomography data collected on thin crystals, aberration-corrected high-angle annular dark field scanning transmission electron microscopy coupled to energy dispersive x-ray spectroscopy mapping, we reach the conclusion that the structure features corner-sharing SbO6 octahedra and NiSbO9 pairs of face-shared octahedra (or Ni-Sb dumbbells) with either a random orientation of the Ni-Sb dumbbells or nanosized chemical correlations for the dumbbell arrangement. As observed in HP Ba3NiSb2O9 produced through synthesis at 9 GPa, AP Ba1.75Sr1.25NiSb2O9 (x = 1.25) crystallizes in a 3C double perovskite A2BB'O6 cubic structure where A, B, and B' sites are occupied by (Ba + Sr), Sb, and (2/3Ni + 1/3Sb) atoms, respectively. The B' sites, which are randomly occupied by spin-1 Ni2+ and diamagnetic Sb5+, form a face-centered-cubic (FCC) sublattice where the Ni2+ amount stays above the site percolation threshold. Weiss temperatures (eta -65 and ti -213 K for Ba2.5Sr0.5NiSb2O9 and Ba1.75Sr1.25NiSb2O9, respectively) indicate that dominant magnetic interactions between Ni2+ spins are antiferromagnetic with magnitudes like those observed in the corresponding HP phases of pure Ba3NiSb2O9. As for the 6H HP Ba3NiSb2O9 compound, in 6H Ba2.5Sr0.5NiSb2O9, muon spin relaxation (mu SR) measurements identify a dynamic magnetic state down to the base temperature (95 mK), consistent with a previously published inelastic neutron scattering study. For 3C Ba1.75Sr1.25NiSb2O9, mu SR and 121Sb nuclear magnetic resonance measurements both indicate the presence of a transition to a static magnetic state below 11(1) K with a significant amount of disorder in this frozen state, in contrast to the spin-liquid state previously suggested for the 3C HP phase of Ba3NiSb2O9. Consistently, a broad maximum is observed in the specific heat at the same temperature. Building on the structural data, the magnetic properties of HP 6H Ba3NiSb2O9 and AP 6H Ba2.5Sr0.5NiSb2O9 are discussed in light of recent works on triangular and J(1) -J(2) honeycomb systems with or without quenched disorder. We are led to the conclusion that the driving force toward a spin-liquid-like state is quenched disorder which needs to be incorporated in J(1) -J(2) honeycomb models. Our evidence of a magnetic transition to a frozen magnetic ground state for the AP Sr-doped 3C phase is in line with models for geometrically frustrated FCC antiferromagnets. This calls for a better experimental and possibly theoretical understanding of the HP 3C phase.

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.

Opal glasses fabricated by Arc (Arques, France) are glass-ceramics that consist of a glassy matrix mainly constituted of silicon dioxide with well crystallized fluoride compounds as inclusions. These later (ca. 8 vol%) play the role of light scattering centers leading to the well-known milky feature of the commercialized glassware, dinnerware products. Their overall chromatic characteristics strongly depend on few parameters (e.g. the refractive indexes of the glass and the ceramic(s), the concentration of inclusions, their mean size, the surface roughness of the article, etc) that have to be determined and controlled during the manufacturing process to end at the product with the desired optical properties. Using a transfer matrix formalism, the 4-flux method can indeed be used to anticipate the transmittance and reflectance of an object for different set of parameters. The impact of each aforementioned parameter on the color rendering will be here separately discussed, and simulations will be confronted to experimental data to assert their validity and their interest to the genesis of new products with targeted optical properties.

A mechanochromic luminescent copper iodide cluster is reported whose luminescence is exalted in response to mechanical stress. The underlying mechanism has been investigated along with the preparation of mechanically responsive films.

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 analysis and Rietveld refinement of X-ray diffraction data, we find that their crystal structure is similar to that of bulk-MnWO4, despite a mean crystallite size of 1.0-1.6 nm and a significant deviation of the average chemical composition from MnWO4. The chemical formula derived from elemental and thermogravimetric analyses is Mn0.8WO3.6(OH)0.4·3H2O. X-ray absorption and magnetic susceptibility measurements show that Mn and W have the same oxidation states as in MnWO4. No magnetic ordering or spin glass or superparamagnetic behavior is observed above 2 K, unlike in the case of MnWO4 nanocrystals having a mean size higher than 10 nm.

Reduction of the size of a particle down to a few tens of nanometers or below may drastically affect its physical properties. That is well-known for quantum dots. Conversely, many works consider the chemical composition of nanoparticles as invariant upon reduction of their dimension. Here we demonstrate that the chemical composition of a transition-metal oxide, namely, nickel oxide, is drastically affected by its nanostructuration.

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) Å. 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.