Krypton irradiation damage in Nd-doped zirconolite and perovskite

Understanding the effect of radiation damage and noble gas accommodation in potential ceramic hosts for plutonium disposition is necessary to evaluate their long-term behaviour during geological disposal. Polycrystalline samples of Nd-doped zirconolite and Nd-doped perovskite were irradiated ex situ with 2 MeV Kr+ at a dose of 5 × 1015 ions cm−2 to simulate recoil of Pu nuclei during alpha decay. The feasibility of thin section preparation of both pristine and irradiated samples by Focused Ion Beam sectioning was demonstrated. After irradiation, the Nd-doped zirconolite revealed a well defined amorphous region separated from the pristine material by a thin (40–60 nm) damaged interface. The zirconolite lattice was lost in the damaged interface, but the fluorite sublattice was retained. The Nd-doped perovskite contained a defined irradiated layer composed of an amorphous region surrounded by damaged but still crystalline layers. The structural evolution of the damaged regions is consistent with a change from orthorhombic to cubic symmetry. In addition in Nd-doped perovskite, the amorphisation dose depended on crystallographic orientation and possibly sample configuration (thin section or bulk). Electron Energy Loss Spectroscopy revealed Ti remained in the 4+ oxidation state but there was a change in Ti coordination in both Nd-doped perovskite and Nd-doped zirconolite associated with the crystalline to amorphous transition

The shape and composition of interstellar silicate grains

We investigate the composition and shape distribution of silicate dust grains in the interstellar medium. The effect of the amount of magnesium in the silicate lattice is studied. We fit the spectral shape of the interstellar 10 mu extinction feature as observed towards the galactic center. We use very irregularly shaped coated and non-coated porous Gaussian Random Field particles as well as a statistical approach to model shape effects. For the dust materials we use amorphous and crystalline silicates with various composition and SiC. The results of our analysis of the 10 mu feature are used to compute the shape of the 20 mu silicate feature and to compare this with observations. By using realistic particle shapes we are, for the first time, able to derive the magnesium fraction in interstellar silicates. We find that the interstellar silicates are highly magnesium rich (Mg/(Fe+Mg)>0.9) and that the stoichiometry lies between pyroxene and olivine type silicates. This composition is not consistent with that of the glassy material found in GEMS in interplanetary dust particles indicating that these are, in general, not unprocessed remnants from the interstellar medium. Also, we find a significant fraction of SiC (~3%). We discuss the implications of our results for the formation and evolutionary history of cometary and circumstellar dust. We argue that the fact that crystalline silicates in cometary and circumstellar grains are almost purely magnesium silicates is a natural consequence of our findings that the amorphous silicates from which they were formed were already magnesium rich.Comment: Accepted for publication in A&

Krypton irradiation damage in Nd-doped zirconolite and perovskite as potential ceramics for inert matrix fuel and plutonium disposition

ABSTRACT Understanding the effect of radiation damage and noble gas accommodation in potential ceramic hosts for plutonium disposition is necessary to evaluate the long-term behaviour during geological disposal. Polycrystalline samples of Nd-doped zirconolite and Nd-doped perovskite were irradiated ex-situ with 2 MeV Kr + at a dose of 5x10 15 ions.cm -2 to simulate plutonium nuclei recoil during alpha decay. The feasibility of thin section preparation of both pristine and irradiated samples by Focussed Ion Beam sectioning was demonstrated. After irradiation, the Nd-doped zirconolite revealed a well defined amorphous region separated from the pristine material by a thin (40-60 nm) damaged interface. The Nd-doped perovskite contained a defined irradiated region composed of an amorphous region surrounded by damaged regions. In both samples, as revealed by electron diffraction, the damaged regions and interface have a structure in which the fluorite sublattice is present while the pristine lattice is absent. In addition in Nddoped perovskite, the amorphisation dose depended on crystallographic orientation and possibly sample configuration (thin section and bulk). In Nd-doped perovskite, Electron Energy Loss Spectroscopy study revealed a change in Ti coordination associated with the crystal to amorphous transition

Low-temperature electrodeposition approach leading to robust mesoscopic anatase TiO2 films

Anatase TiO2, a wide bandgap semiconductor, likely the most worldwide studied inorganic material for many practical applications, offers unequal characteristics for applications in photocatalysis and sun energy conversion. However, the lack of controllable, cost-effective methods for scalable fabrication of homogeneous thin films of anatase TiO2 at low temperatures (ie. < 100 °C) renders up-to-date deposition processes unsuited to flexible plastic supports or to smart textile fibres, thus limiting these wearable and easy-to-integrate emerging technologies. Here, we present a very versatile template-free method for producing robust mesoporous films of nanocrystalline anatase TiO2 at temperatures of/or below 80 °C. The individual assembly of the mesoscopic particles forming ever-demonstrated high optical quality beads of TiO2 affords, with this simple methodology, efficient light capture and confinement into the photo-anode, which in flexible dye-sensitized solar cell technology translates into a remarkable power conversion efficiency of 7.2% under A.M.1.5G conditions

Interlayer strain effects on the structural behavior of BiFeO3/LaFeO3 superlattices

Artificial (BiFeO3)0.5Λ/(LaFeO3)0.5Λ superlattices have been grown by pulsed laser deposition. The periodicity Λ was varied from 150 Å to 25 Å and the relative ratio between BiFeO3 (BFO) and LaFeO3 (LFO) is kept constant in each period. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy investigations indicate antiferroelectric-like structures for large periodicity (Λ ≥ 76 Å), while Pnma LaFeO3-like structures are observed for small periodicity Λ ≤ 50 Å. Room temperature magnetic measurements were obtained by vibrating sample magnetometry and suggest antiferromagnetic ordering with weak ferromagnetism. Temperature dependent x-ray diffraction studies show an important shift of paraelectric-antiferroelectric phase transition scaling with BFO thickness. Strain and size effects explain this behavior and discussion is also made on the possible role of the oxygen octahedral rotation/tilt degree of freedom

The origin of GEMS in IDPs as deduced from microstructural evolution of amorphous silicates with annealing

We present laboratory studies of the micro-structural evolution of an amorphous ferro-magnesian silicate, of olivine composition, following thermal annealing under vacuum. Annealing under vacuum was performed at temperatures ranging from 870 to 1020 K. After annealing spheroidal metallic nano-particles (2-50 nm) are found within the silicate films. We interpret this microstructure in terms of a reduction of the initial amorphous silicate FeO component, because of the carbon-rich partial pressure in the furnace due to pumping mechanism. Annealing in a controlled oxygen-rich atmosphere confirms this interpretation. The observed microstructures closely resemble those of the GEMS (Glass with Embedded Metal and Sulphides) found in chondritic IDPs (Interplanetary Dust Particles). Since IDPs contain abundant carbonaceous matter, a solid-state reduction reaction may have occurred during heating in the hot inner regions of the proto-solar disc. Related to this, the presence of forsterite grains grown from the amorphous precursor material clearly demonstrates that condensation from gaseous species is not required to explain the occurrence of forsterite around young protostars and in comets. Forsterite grains in these environments can be formed directly in the solid phase by thermal annealing of amorphous ferro-magnesian silicates under reducing conditions.Comment: 4 pages, 2 figures. Accepted for publication A&A Letter to the Edito

Boron-Based Functional Additives Enable Solid Electrolyte Interphase Engineering in Calcium Metal Battery

Calcium-metal batteries have received growing attention recently after several studies reporting successful metal plating and stripping with organic electrolytes. Given the low redox potential of metallic calcium, its surface is commonly covered by a passivation layer grown by the accumulation of electrolyte decomposition products. The presence of borate species in this layer has been shown to be a key parameter allowing for Ca2+ migration and favoring Ca electrodeposition. Here, boron-based additives are evaluated in order to tune the SEI composition, morphology, and properties. The decomposition of a BF3-based additive is studied at different potentiostatic steps and the resulting SEI layer was thoroughly characterized. SEI growth mechanism is proposed based on both experimental data and DFT calculations pointing at the formation of boron-crosslinked polymeric matrices. Several boron-based adducts are explored as SEI-forming additives for calcium-metal batteries paving the way to very rich chemistry leading to Ca2+ conducting SEI.Funding from the European Union's Horizon 2020 research and innovation program H2020 are acknowledged: European Research Council (ERC-2016-STG, CAMBAT, grant agreement no. 715087 and ERC-2020-STG, HiPeR−F, grant agreement no. 950625) and H2020-MSCA-COFUND-2016 (DOC-FAM, grant agreement no. 754397). A.P. is grateful to the Spanish Ministry for Economy, Industry and Competitiveness Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S). D.F., C.C. and R.D. thank the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01) for financial support. K.R. and M.L. gratefully acknowledge the research funding by the Slovenian Research Agency (P1-0045, N1-0189). Alistore-European Research Institute is gratefully acknowledged for financial support through the postdoc grant to C.B. The SR-FTIR experiments were performed at MIRAS beamline at ALBA Synchrotron with the collaboration of ALBA staff. All DFT calculations were carried out at the Wroclaw Centre for Networking and Supercomputing within grant no. 346.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Resistance to amorphisation in Ca1-xLa2x/3TiO3 perovskites – a bulk ion-irradiation study

The changes induced from 1 MeV Kr+ and 5 MeV Au+ ion irradiation at room temperature have been utilised to determine the impact of cation vacancies on the radiation damage response of bulk Ca1-xLa2x/3TiO3 perovskite structured ceramics. Perovskite systems have long been considered as candidate waste forms for the disposition of actinide wastes, and doping with multi-valent elements such as Pu may lead to cation deficiency. Based on GAXRD and TEM analysis, two regions of resistance/susceptibility to amorphisation have been confirmed with reference to CaTiO3. Increased resistance to amorphisation has been observed for 0.1 ≤ x ≤ 0.4, with an increased susceptibility to amorphisation for x ≥ 0.5. It is proposed that these processes are induced by enhanced recovery from radiation damage for 0.1 ≤ x ≤ 0.4, and reduced tolerance for disorder/the increasingly covalent nature of the A-O bond for x ≥ 0.5. Lattice parameter analysis of the x = 0 and 0.5 samples showed a saturation in radiation damage induced volume swelling at 4.7 ± 0.1% and 1.8 ± 0.1%, respectively, while the saturation limit for the b parameter was lower than the respective a and c orthorhombic parameters. In the x = 0.2 and 0.4 samples, amorphisation was not observed, however the b parameter was found to swell to a lesser extent than the a and c parameters. Swelling was not observed for the ion irradiated x ≥ 0.6 samples

Évolution des silicates dans les milieux interstellaires, circumstellaires et cométaires (le rôle de l'irradiation et de la température)

Suite au développement des techniques d'observation et d'analyse, notre connaissance de la poussière silicatée dans les environnements astrophysiques a beaucoup évolué. Le cycle de vie de la poussière débute aœc sa formation autour des étoiles en fin de vie. Par la pression des vents stellaires, elle est ensuite injectée dans le milieu interstellaire (MIS) dans lequel elle transite. Enfin, elle peut être incorporée dans les disques d'accrétion autour des étoiles jeunes. Lors de ces différentes étapes, elle est soumise à diverses sollicitations qui induisent des modifications structurales ou chimiques. L'un des objectifs de cette thèse est d'abord de déterminer les modifications chimiques et morphologiques de la poussière silicatée quand elle est soumise à une irradiation ionique dans les ondes de choc de supernovae. Pour cela, nous avons effectué des expériences d'irradiation ionique (H+ et He+) à basse énergie in situ dans un spectroscope de photoélectrons (XPS). Les suivis chimiques et morphologiques ont été réalisés par XPS et par microscopie à force atomique. Le second objectif de cette thèse est d'indiquer comment la poussière amorphe évolue lors de son incorporation dans les régions internes du dIsque d'accrétion autour des étoiles jeunes. Nous avons ainsi mis en place des traitements thermiques de silicates amorphes in situ dans un microscope électronique en transmission (MET) et en four sous atmosphère contrôlée. Les évolutions microstructurales et chimiques ont été observées à l'aide d'un MET associé à un spectroscope à dispersion d'énergie. Nous avons montré qu'une irradiation ionique induit des modifications chimiques et morphologiques. Dans le milieu mterstellaire, les ondes de choc de supernovae sont donc des évènements très propices à modifier les matériaux initialement issus des étoiles en fin de vie. Les produits de recristallisation obtenus suite aux recuits sont très dépendants de la pression partielle d'oxygène imposée. Les microstructures obtenues sont souvent comparables avec celles observées dans les objets les plus primitifs de notre système solaire (poussière interplanétaire ou cométaire) La recristallisation du précurseur interstellaIre dans la partie interne du disque d'accrétion est donc un moyen pour former des phases qui sont ensuite incorporées dans les astéroïdes ou les comètes.LILLE1-BU (590092102) / SudocSudocFranceF