46 research outputs found
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
Interlayer strain effects on the structural behavior of BiFeO3/LaFeO3 superlattices
Artificial (BiFeO3)0.5Î/(LaFeO3)0.5Î superlattices have been grown by pulsed laser deposition. The periodicity Î was varied from 150âĂ
to 25âĂ
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 (Î â„ 76âĂ
), while Pnma LaFeO3-like structures are observed for small periodicity Π†50âĂ
. 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
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 Ă 1015 ions cmâ2 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 (40â60 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
Resistance to amorphisation in Ca1-xLa2x/3TiO3 perovskites â a bulk ion-irradiation study
The changes induced from 1âŻMeV Kr+ and 5âŻMeV 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 0.1âŻâ€âŻxâŻâ€âŻ0.4, with an increased susceptibility to amorphisation for xâŻâ„âŻ0.5. It is proposed that these processes are induced by enhanced recovery from radiation damage for 0.1âŻâ€âŻxâŻâ€âŻ0.4, and reduced tolerance for disorder/the increasingly covalent nature of the A-O bond for xâŻâ„âŻ0.5. Lattice parameter analysis of the xâŻ=âŻ0 and 0.5 samples showed a saturation in radiation damage induced volume swelling at 4.7âŻÂ±âŻ0.1% and 1.8âŻÂ±âŻ0.1%, respectively, while the saturation limit for the b parameter was lower than the respective a and c orthorhombic parameters. In the xâŻ=âŻ0.2 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 xâŻâ„âŻ0.6 samples
Growth of single-crystal copper sulfide thin films via electrodeposition in ionic liquid media for lithium ion batteries
By exploiting the ability of ionic liquids to solubilize molecular sulfur at the melting point, we report the electrodeposition of CuS in an [EMIm]TFSI (1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide) electrolytic bath containing Cu(TFSI) 2 salt and elemental sulfur. Single-crystal and preferentially oriented covellite CuS thin films with flake morphology have been successfully obtained. Li/CuS coin cells using the deposits after carbon coating as the positive electrode show a discharge capacity of 350 mA h g -1 with capacity retention of 54.4% after 20 cycles. © The Royal Society of Chemistry 2012
Phase stability frustration on ultra-nanosized anatase TiO 2
cited By 8International audienceThis work sheds light on the exceptional robustness of anatase TiO 2 when it is downsized to an extreme value of 4Ăą âŹâ°nm. Since at this size the surface contribution to the volume becomes predominant, it turns out that the material becomes significantly resistant against particles coarsening with temperature, entailing a significant delay in the anatase to rutile phase transition, prolonging up to 1000Ăą âŹâ°Â°C in air. A noticeable alteration of the phase stability diagram with lithium insertion is also experienced. Lithium insertion in such nanocrystalline anatase TiO 2 converts into a complete solid solution until almost Li 1 TiO 2, a composition at which the tetragonal to orthorhombic transition takes place without the formation of the emblematic and unwished rock salt Li 1 TiO 2 phase. Consequently, excellent reversibility in the electrochemical process is experienced in the whole portion of lithium content
Complex Lithiation Mechanism of Siloxene and Germanane: Two Promising Battery Electrode Materials
International audienceThe layered siloxene and germanane, derived from CaSi 2 and CaGe 2 , respectively, have shown very promising results as anodes for Lithium-ion batteries. Their delivered capacities, capacity retention and high rate cycling are superior compared to bulk Si and Ge. These positive features are most probably related to the layered morphology that buffers the volume changes and improves the kinetics. Despite numerous recently published studies regarding their electrochemical properties, very little is known about their electrochemical mechanism. In this work, we have used a combination of different characterization techniques to study the processes taking place during the lithiation of siloxene and germanane and compared with Si and Ge. Our results suggest a slightly different pathway for the lithiation of siloxene and germanane: their initial layered morphology is preserved after cycling, the crystalline Li 15 Si 4 and Li 15 Ge 4 characteristic of an alloying mechanism are absent and possibly different lithiated intermediates are formed. We provide then, an initial assessment of the involved Li x Si and Li x Ge phases and propose the hypothesis of a reversible Li intercalation in the siloxene and germanane layers