New nuclear glass compositions, able to immobilize highly active liquid wastes arising from high burn-up UO2 fuel reprocessing, are being studied. Investigations are being performed on rare earthrich glasses, known as durable matrices. After a preliminary study, a basic glass composition was selected (Glass A, wt. %) : 51.0 SiO2 – 8.5 B2O3 – 12.2 Na2O – 4.3 Al2O3 – 4.8 CaO – 3.2 ZrO2 – 16.0 Nd2O3. The aim of this study is to determine the local environment of the rare earth in this glass and its evolution according to neodymium. To achieve this objective, glasses were prepared from the baseline Glass A with variable neodymium oxide amounts (from 0 to 30 wt. % Nd2O3). By coupling characterization methods such as EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy at the neodymium LIII-edge, optical absorption spectroscopy, B, Al MAS-NMR and Raman spectroscopy, pieces of information on the rare earth surroundings in the glass were obtained.

This work concerns glasses belonging to SiO2-Al2O3-CaO-ZrO2-TiO2-Nd2O3 system that lead to zirconolite crystallization in their bulk after nucleation + crystal growth thermal treatments and that could find application as nuclear waste form. The understanding of crystallization processes in glasses implied to investigate their structure. The environment around Ti, Zr (nucleating agents) and Nd was characterized for various Nd2O3 loadings. Electron spin resonance study of the small amount of Ti3+ occurring in glasses enabled to identify two types of sites for titanium. EXAFS showed that Zr occupied a quite well defined 6-7-fold site coordinated by oxygen at 2.20 {\AA}, with second neighbors that could correspond to Ca/Ti and Zr around 3.5 {\AA}. This short range order presents some similarities with zirconolite, which could predispose glass to zirconolite nucleation. Nd environment was probed by optical spectroscopies, ESR and EXAFS. Results showed that the environment around Nd was very constrained by the glassy network and significantly differed from the one in zirconolite. Nd occupied a highly distorted 8-9-fold coordinated site in glass with oxygen atoms at 2.53 {\AA}. No second neighbors were clearly identified by EXAFS around Nd, but the study of Nd optical fluorescence decays suggested a strong interaction between Nd ions.

The investigations on enhanced reprocessing of nuclear spent fuel, and notably on separating the long-lived minor actinides, such as Am and Cm, from the other fission products have led to the development of highly durable specific matrices such as glass-ceramics for their immobilization. This study deals with the characterization of zirconolite (CaZrTi 2 O 7 ) based glass-ceramics synthesized by devitrification of an aluminosilicate parent glass. Trivalent actinide ions were simulated by neodymium, which is a paramagnetic local probe. Glass-ceramics with Nd 2 O 3 contents ranging from 0 to 10 weight % were prepared by heat treatment of a parent glass at two different growth temperatures: 1050° and 1200°C. X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and electron spin resonance (ESR) measurements clearly indicate that Nd 3+ ions are partly incorporated in zirconolite crystals formed in the bulk of the glass-ceramic samples. The amount of neodymium in the crystalline phase was estimated using ESR results and was found to decrease with increasing either heat treatment temperature or total Nd 2 O 3 content.

Light and flexible optical batteries based on plastic lithium-ion battery (PliON) technology have been recently proposed, and are able to modulate their reflection in the infrared range. We have focused our interest in the wavelength range 3–5 and 8–12μm range corresponding to two optical windows of light propagation in the atmosphere. The original feature of this device is that it uses material powder embedded in a plastic matrix. The choice of materials to obtain significant contrasts is discussed. According to the type of materials (metal or semiconductor), the influence of their nature, their morphology and their structures on the optical properties is underlined. The optical behaviors of low or high absorptive compounds have been understood and correlated to the particle size. The main important point is that high reflection can be obtained with high absorptive or transparent particles unlike the thin layer device. Some parameters are investigated in order to improve to final device.

Dielectric and conductivity spectra of a Li0.2V2O5 thin film were recorded in a broad frequency range 40–1.1×108Hz at temperature varying between 210 and 300K. The V2O5 thin film (thickness 260nm) was deposited on titanium substrate by atomic layer deposition (ALD). An annealing process at 500°C in air was required to obtain crystallized V2O5. Li0.2V2O5 were obtained by electrochemical insertion of lithium ions within V2O5 thin film. All the data are presented in the form of complex resistivity and permittivity diagrams which have been analyzed in relation to characterizations with scanning electron microscopy (SEM) and X-ray diffraction (XRD). The Dc-conductivity σDc of Li0.2V2O5 film is induced by a surface diffusion of small-polarons on particles (submicrostructure) and crystallites (nanostructure), which constitute the film texture.

Glass-ceramics containing neodymium-rich crystalline phases can be obtained by crystallization of silicate glasses (nucleation+crystal growth heat treatments) or by controlled cooling of melts. Such materials could be envisaged as durable matrices for conditioning minor actinides- and Pu-rich nuclear wastes if the partitioning ratio of the wastes between crystalline phase and residual glass is high (principle of double containment barrier). In radioactive waste forms, Nd would be partially substituted by actinides and neutron absorbers (Gd). In this work, two silicate glass compositions leading to efficient nucleation and crystallization of either zirconolite (Ca1−xNdxZrTi2−xAlxO7, x<1) or apatite (Ca2Nd8Si6O26) in their bulk were studied as potential waste forms. The effect of the method used to prepare glass-ceramics (controlled cooling from the melt or nucleation+crystal growth from the glass) on both the microstructure and the structure of the neodymium-rich crystalline phase was studied. The highest number of zirconolite or apatite crystals in the bulk was obtained using the nucleation+crystal growth method. However, the percentage of neodymium incorporated in zirconolite crystals remained too small to make realistic the use of such materials for the conditioning of actinides in comparison with more durable bulk ceramics.

New nuclear highly durable glass compositions, able to immobilize a higher concentration of high-level nuclear wastes than current borosilicate nuclear glasses, are being studied Investigations are performed on rare earth (RE)-rich glasses, known as durable matrices. After a preliminary study on complex and simplified compositions, a basic glass composition was selected and studied (wt%): 51.0 SiO2-8.5 B2O3-12.2Na(2)O-4.3Al(2)O(3)-4.8CaO-3.2ZrO(2)-16.0RE(2)O(3). Chemical durability, physical properties (viscosity, transformation temperature), and crystallization tendency of glasses containing either a mixture of RE (La + Ce + Pr + Nd) or only one RE were studied and compared The local environment of RE (for RE = Nd) in the glass and its evolution according to Nd2O3 concentration (from 1.3 to 30 wt%) was also studied by coupling characterization methods such as extended X-ray absorption fine structure spectroscopy at the neodymium L-111-edge and optical absorption spectroscopy. B-11, Al-27 magic angle spinning-nuclear magnetic resonance, and Raman spectroscopy were also used to study glass structure.

Low temperature synthesis and electrochemical properties of partially substituted lithium manganese oxides are reported. We demonstrate various metallic cations (Cu2+, Ni2+, Fe3+, Co3+) can be incorporated in the 3 V layered cathodic material Li0.45MnO2.1. New compounds Li0.45Mn0.88Fe0.12O2.1, Li0.45Mn0.84Ni0.16O2.05, Li0.45Mn0.79Cu0.21O2.3, Li0.45Mn0.85Co0.15O2.3 are prepared. These 3 V cathode materials are characterized by the same shape of discharge-charge profiles but different values of the specific capacity, between 90 mAh g−1 and 180 mAh g−1. The best results in terms of capacity and cycle life are obtained with the selected content of 0.15 Co per mole of oxide, as the optimum composition. The high kinetics of Li+ transport in Li0.45Mn0.85Co0.15O2.3 compared to that in the Co-free material is consistent with a substitution of Mn(III) by Co(III) in MnO2 sheets.

Dielectric and conductivity spectra of a V2O5 thin film were recorded in a broad frequency range 40–1.1 × 108 Hz at temperatures varying between 205 and 297 K. The V2O5 thin film (thickness 260 nm) was deposited on titanium substrate by atomic layer deposition (ALD). An annealing process at 500 °C in air was required to obtain crystallized V2O5. All the data are presented in the form of complex resistivity diagrams which have been analyzed in relation to characterizations with scanning electron microscopy (SEM) and X-ray diffraction (XRD). These diagrams show the existence of relaxations due to interfacial polarization phenomena (grain boundary polarization) within the sample, which permits the determination of the dc-conductivity of the grain (monocrystal). A dielectric relaxation is found, attributed to non-adiabatic small polaron hopping. The corresponding relaxation frequency is thermally activated with an activation energy of 0.14 eV. The experimental results enabled us to determine the drift mobility of the small polarons, i.e.μD = 1.84 × 10−2 cm2 V−1 s−1 at room temperature.

Glass-ceramic matrices containing zirconolite (nominally CaZrTi2O7) as the only crystalline phase in their bulk can be considered as good candidates for actinide-rich nuclear wastes (containing minor actinides or Pu) immobilization. In this study, three different methods are envisaged and compared to prepare such waste forms using neodymium as trivalent actinides surrogate. Independently on the preparation method, zirconolite is shown to be the only crystalline phase to nucleate in the bulk. However, crystallization of silicate phases (titanite CaTiSiO5 + anorthite CaAl2Si2O8) can occur from samples surface and can compete with zirconolite crystallization. The effect of the crystal growth thermal treatment duration (2-300 h) at high temperature (1050-1200degreesC) on glass-ceramics structure and microstructure is studied. In the oxides system studied here, it appears that zirconolite is not thermodynamically stable in comparison with titanite but, for kinetics reasons, such transformation will not occur during waste forms disposal.

Progress on separating the long-lived fission products has notably implied basic research on specific host matrices, especially for the immobilization of cesium. Barium hollandite (BaAl2Ti6O16) ceramics have received considerable interest because of their high cesium incorporation ability and chemical stability. This study deals with the preparation of hollandite in the BaxCsy(Al,Fe)2x+yTi8–2x-yO16 (x+y<2) compositional range by an oxide route. Different parameters such as the grain size of the precursor or the temperature and duration of sintering were changed in order to optimize ceramics synthesis. To estimate the hollandite radiation resistance, external electron irradiation experiments (simulating the β particles emitted by radioactive cesium) were performed on hollandite of simple composition. The irradiation-induced defects were studied by Electron Paramagnetic Resonance (EPR) spectroscopy and their nature is discussed.

Progress on separating the long-lived fission products from the high level radioactive liquid waste (HLW) has led to the development of specific host matrices, notably for the immobilization of cesium. Hollandite (nominally BaAl2Ti6O16), one of the main phases constituting Synroc, receives renewed interest as specific Cs-host wasteform. The radioactive cesium isotopes consist of short-lived 134Cs and 137Cs of high activities and 135Cs with long lifetime, all decaying according to Cs+→Ba2++e− (β) + γ. Therefore, Cs-host forms must be both heat and (β,γ)-radiation resistant. The purpose of this study is to estimate the stability of single phase hollandite under external β and γ radiation, simulating the decay of Cs. A hollandite ceramic of simple composition (Ba1.16Al2.32Ti5.68O16) was essentially irradiated by 1 and 2.5 MeV electrons with different fluences to simulate the β particles emitted by cesium. The generation of point defects was then followed by Electron Paramagnetic Resonance (EPR). All these electron irradiations generated defects of the same nature (oxygen centers and Ti3+ ions) but in different proportions varying with electron energy and fluence. The annealing of irradiated samples lead to the disappearance of the latter defects but gave rise to two other types of defects (aggregates of light elements and titanyl ions). It is necessary to heat at relatively high temperature (T=800°C) to recover an EPR spectrum similar to that of the pristine material. The stability of hollandite phase under radioactive cesium irradiation during the waste storage is discussed.

Nuclear power reactors generate long-lived radionuclides such as minor actinides (Np, Am, Cm) which are mainly responsible for the long term radiotoxicity of high level nuclear wastes obtained after reprocessing of nuclear spent fuel. Specific highly durable matrices such as glass-ceramics appear as good candidates for the immobilization of minor actinides. This work concerns the synthesis and the characterization of zirconolite (CaZrTi2O7) based glass-ceramics prepared by controlled devitrification of (TiO2, ZrO2)-rich SiO2-Al2O3-CaO parent glasses for which neodymium was selected to simulate the radioactive trivalent minor actinides. The present study reports the effect of increasing TiO2, ZrO2 and CaO amounts in glass composition on the structure and the composition of the zirconolite crystals (formed as the only crystalline phase in the bulk of the glass), on their nucleation rate I(Z) and on the volume proportion of crystalline phase V of the glass-ceramics. It appears that I(Z) and V strongly increase when the parent glass composition changes. Neodymium electron spin resonance (ESR) shows that the total amount of Nd3+ ions incorporated in the zirconolite phase increases with TiO2, ZrO2 and CaO amounts in parent glass composition.

Conductivity and resistivity spectra of the compounds LixWO3.H2O (X = 0, 0.05 and 0.25) are reported and analyzed. The spectra were recorded for compacted powders within the broad frequency range 10(3) - 10(10) Hz at temperature varying between 200 and 300 K. The complex resistivity plots allowed the determination of the bulk dc-conductivity of LixWO3.H2O versus temperature. The conduction behavior is interpreted in terms of hopping and tunneling of small-polarons in the oxide network.

The structural and electrochemical behavior of o-LixWO3·H2O has been studied for several electrochemical Li intercalation/deintercalation processes. Four intercalated phases called α, β, γ and δ, were distinguished by means of in situ X-ray diffraction (XRD) experiments. The modification in the distance between the tungsten layers represented by the cell lattice parameter b was found to reflect the structural changes induced by Li intercalation. Thus, we found that potential cycling over the α phase (till x=0.35) does not lead to any major degradation of the structure whereas reducing further WO3·H2O and reaching the β, γ or δ phase introduces irreversible damages. Furthermore, the α intercalation domain divides into three subphases called α0, α1 and α2. From the less intercalated phase to the most intercalated one, the structure exhibits increasing higher symmetry. The unintercalated orthorhombic cell (α0 phase) first changes into a quasi-quadratic one where a≈c≠b/2 (α1 phase) and finally to a quasi-quadratic one where a≈c≈b/2 (α2 phase). The knowledge of this intercalation behavior is essential to improve the performance of a recently built WO3·H2O-based variable infrared reflectance plastic device.

The main electrochemical properties of 3 V manganese oxides Li(0.45)MnO(2.1) and Li(0.45)Mn(0.85)CO(0.15)O(2.3) synthesized via a solution technique are reported. These materials are characterized by an attractive cycle life with a stable specific capacity in the voltage range 4.2-2 V between 165 and 195 mAh g(-1) depending the C rate and the compound. Impedance spectroscopy is used to evaluate the chemical diffusion coefficient of lithium in both cathodic materials. D(Li) is found to be twofold higher in the Co-doped compound and little affected by Li concentration in the composition range 0.45 < x < 0.85. Analysis of impedance diagrams supports the existence of a passivating layer (Li(+)-ion conducting layer) onto the electrode when propylene carbonate is used as solvent or cosolvent. The presence of cobalt promotes the formation of this surface layer. (C) 2002 Elsevier Science Ltd. All rights reserved.

Controlled crystallization of (TiO2-ZrO2)-rich calcium aluminosilicate glasses led to zirconolite in the bulk, and titanite and anorthite on the surface. Such glass-ceramics can be envisaged for minor actinides immobilization. In this study, the crystallization of three glass compositions with increasing TiO2, ZrO2 and CaO amounts was followed by differential thermal analysis (DTA). The effect of glass particle size and of heating rate on DTA curves was studied in order to investigate nucleation mechanisms and to extract the corresponding crystal growth activation energies Ec for the different crystalline phases. Exothermic effects associated with the crystallization of a phase having a defect-fluorite structure in the bulk and its consecutive transformation into zirconolite were only detected for the highly TiO2, ZrO2 and CaO enriched glasses due to their higher crystallization rate. Using an Avrami constant n = 3 and a dimensionality of crystal growth m = 3, the activation energy of defect-fluorite crystal growth was found to be Ec = 440 kJ · mol−1 (modified Kissinger method). Titanite and anorthite grow only from glass surface with activation energies of respectively 493 and 405 kJ · mol−1 (n = m = 1, Kissinger method). DTA study of melt crystallization during cooling showed that baddeleyite (ZrO2) crystals firstly crystallize but become unstable versus zirconolite for higher undercooling.

New glassy matrices, able to incorporate new highly concentrated radioactive liquid wastes (HLW), are being studied. Investigations were performed on rare earth-rich glasses, known as very durable matrices. The selected basic glass composition was (wt. %): 51.0 SiO 2 –8.5 B 2 O 3 –12.2 Na 2 O–4.3 Al 2 O 3 –4.8 CaO–3.2 ZrO 2 –16.0 Nd 2 O 3 . To determine both the environment around the rare earth in this glass and its evolution according to its concentration (1.3–30 wt. % Nd 2 O 3 ), EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy at the LIII-edge of neodymium and optical absorption spectroscopy were used. By coupling these two characterisation methods, several hypotheses are proposed about the nature of the rare earth neighbouring in the glass.

Instead of the usual sputtered anhydrous tungsten oxide thin films, a powder of monohydrated tungsten oxide (WO3.H2O) was used for the making of an electrochromic infrared emissivity modulator. The WO3.H2O powder was embedded in a porous plastic matrix before being laminated with other appropriate layers of the battery-like device, leading then to a complete flexible emissivity modulator. The widely open structure of the hydrated tungsten oxide makes lithium intercalation easier, which is particularly suitable for the realization of plasticized devices. Compared to a classical battery assembly, a porous plastic graphite layer laminated with a conductive grid was sandwiched between the WO3.H2O and the electrolyte layers. Such an original device allowed both a perfect uniformity in current collection and a sufficient porosity for the liquid electrolyte displacement. The complete device demonstrated a satisfying electrochemical behavior under 1 mV/s potential sweeps, allowing the insertion of a large amount of lithium ions into the WO3.H2O structure. Hemispherical reflectance measurements were carried out both over the VIS/NIR (0.4–2.5 μm) and the mid-infrared (2.5–25 μm) spectral ranges. Reflectance over the 2.5–25 μm spectral range was found to switch from 2% to 32% upon intercalation of 0.65 Li per tungsten. This value is comparable to previous literature results obtained for rigid devices.