The use of ceramics as radionuclide containment matrices for the safe long-term storage and disposal of high-level nuclear waste is studied with emphasis on chemistry flexibility, structural stability, and radiation tolerance. Here we investigate the flexibility of a particular series of compounds Yb2Ti2-xO7-2x (x = 0, 0.2, 0.52, 0.8, and 1) to form a solid solution between the end members Yb2Ti2O7 of pyrochlore structure through to Yb2TiO5 of fluorite structure. Whilst it is shown that cation disorder and corresponding transition from the ordered pyrochlore to disordered fluorite is facilitated via increasing the ytterbium to titanium ratio, it is also shown that sintering conditions may be controlled in such a way as to encourage the growth of the pyrochlore structure even in Yb2TiO5. The radiation response of these materials was tested in situ via 1 MeV krypton irradiation coupled with transmission electron microscopy characterisation. The critical fluence of ions required to transition the crystalline phase to amorphous was found to increase with increasing disorder from Yb2Ti2O7 to Yb2TiO5. However, of the two forms (pyrochlore and fluorite) of Yb2TiO5 studied via ion irradiation that with the greater pyrochlore structure and so more ordered also had the lower critical temperature, 434 K, for maintaining crystallinity during irradiation.

The design of radiation-tolerant polycrystalline materials has been mainly based on the control and manipulation of grain boundaries (GBs) that leads to annihilation of point defects at grain-boundary neighborhoods thus resulting in the formation of defect denuded zones. Nanocrystalline materials are potential candidates providing large density defect sinks for individual point defects and small highly mobile defect clusters (DCs). Using the in-situ irradiation transmission electron microscopy (TEM) technique, this study not only experimentally revealed the coalescence of small glissile DCs at/near GB and their subsequent annihilation at grain-boundary, but also provide insight into defect cluster dynamics. The small DCs were found to be transported to grain-boundary neighborhoods where they can annihilate by the onedimensional loop hop or Burgers-vector rotation mechanism to GBs, considered as the main contribution to the long-range flux of interstitials to GB sinks. This process had marked effects on the morphology of the irradiated microstructure in nanocrystalline iron, limiting the length of DC strings and reducing the coalescence of DCs into large clusters (dislocation loops).(c) 2022 Published by Elsevier B.V.

While transformations of dislocation-loop character at high temperatures during heavy ion irradiation has been studied for more than two decades, the role of grain size, or high sink density, has not been considered. To interrogate the effect of defect mobility on irradiated nanocrystalline (nc) microstructures at elevated temperatures, detailed in-situ ion irradiation transmission electron microscopy (TEM) studies were carried out. The transformation temperature for the Burgers vector b = 1/2 <111>-to-<100> transition was found to be 450 °C, representing a lower threshold than that found in micron-grain-sized counterparts. The formation of stable b = 1/2<111> dislocation loops is observed below 400 °C, while at 450∼500 °C, 1/2<111> loops either transformed into 〈100〉 loops or were absorbed at grain boundaries (GBs). Thus, the substantial absorption of point defects and dislocation loops by GBs over a range of temperatures characteristically changes the defect morphology from large finger-shaped observed in micron-sized grains to small circular shape loops in nc grains.

The mechanisms of the sputter induced orientation change in YBa2Cu3O7-x(YBCO) films grown on MgO (001) substrates by pulsed organometallic beam epitaxy (POMBE) are investigated by x-ray diffraction, Rutherford backscatter spectroscopy (RBS), cross-section TEM (XTEM) and microanalysis. It is found that the W atom implantation concurring with the ion sputtering plays an important role in effecting the orientation change. This implantation changes the surface structure of the substrate and induces an intermediate layer in the initial growth of the YBCO film, which in turn acts as a template that induces the orientation change. It seems that the surface morphology change caused by ion sputtering has only a minor effect on the orientation change.

We report for the first time the observation of irradiation-induced amorphization of the zirconium suboxide formed during aqueous corrosion of Zr-0.5Nb alloys. High-resolution transmission electron microscopy results reveal amorphization of the hexagonal-ZrO suboxide under heavy ion irradiation at cryogenic temperatures. This irradiation-induced amorphization behaviour is discussed in relation to the arrangement of oxygen interstitials and the formation of stable superlattices. The sensitivity of the suboxide to irradiation damage can lead to phase changes and the accumulation of defects near the oxide/metal interface, which needs to be taken into account in the development of mechanistic models addressing radiation-assisted acceleration of corrosion rates in zirconium alloys.

We report an original experimental study on a zirconium alloy deformed in situ under ion irradiation and applied stress inside a Transmission Electron Microscope. We observe that dislocations initially pinned on irradiation defects can be unpinned and glide at a lower stress under the effect of the irradiation. It is proposed that unpinning occurs by a local effect of the displacement cascade created by the incoming ion in the vicinity of the pinning point. This novel mechanism of dislocation glide assisted by irradiation is thought to play a crucial role on in-reactor irradiation creep of zirconium alloys.

This ion-irradiation study covers the four major crystal structure types in the Ln(2)TiO(5) series (Ln = lanthanide), namely orthorhombic Pnma, hexagonal P63/mmc, cubic (pyrochlore-like) Fd-3m and cubic (fluorite-like) Fm-3m. This is the first systematic examination of the complete Ln(2)TiO(5) crystal system and the first reported examination of the hexagonal structure. A series of samples, based on the stoichiometry Sm(x)Yb(2-x)TiO5 (where x = 2, 1.4, 1, 0.6, and 0) have been irradiated using 1 MeV Kr2+ ions and characterised in-situ using a transmission electron microscope. Two quantities are used to define ion-irradiation tolerance: critical dose of amorphisation (D-c), which is the irradiating ion dose required for a crystalline to amorphous transition, and the critical temperature (T-c), above which the sample cannot be rendered amorphous by ion irradiation. The structure type plus elements of bonding are correlated to ion-irradiation tolerance. The cubic phases, Yb2TiO5 and Sm0.6Yb1.4TiO5, were found to be the most radiation tolerant, with Tc values of 479 and 697 K respectively. The improved radiation tolerance with a change in symmetry to cubic is consistent with previous studies of similar compounds. (C) 2016 Elsevier B.V. All rights reserved.

Pressurized water reactor (PWR) Zr-based alloy structural materials show creep and growth under neutron irradiation as a consequence of the irradiation induced microstructural changes in the alloy. A better scientific understanding of these microstructural processes can improve simulation programs for structural component deformation and simplify the development of advanced deformation resistant alloys. As in-pile irradiation leads to high material activation and requires long irradiation times, the objective of this work was to study whether ion irradiation is an applicable method to simulate typical PWR neutron damage in Zr-based alloys, with AREVA’s M5® alloy as reference material. The irradiated specimens were studied by electron backscatter diffraction (EBSD), positron Doppler broadening spectroscopy (DBS) and in situ transmission electron microscopy (TEM) at different dose levels and temperatures. The irradiation induced microstructure consisted of - and -type dislocation loops with their characteristics corresponding to typical neutron damage in Zr-based alloys; it can thus be concluded that heavy ion irradiation under the chosen conditions is an excellent method to simulate PWR neutron damage.

Ion channeling in single crystals of (Y/Er)Ba2Cu3O7–δ reveal an abrupt change (~0.01Å) at the superconducting transition temperature (Tc) in displacements of the Cu and O atoms perpendicular to the [001] direction. This anomalous change in atomic displacements shifts directly with stoichiometry-induced changes in Tc. Blocking patterns indicate no large structural changes across Tc.

We present measurements of crystallographic domain tilts in a (001) BiFeO3 thin film using focused beam x-ray nanodiffraction. Films were ferroelectrically pre-poled with an electric field orthogonal and parallel to as-grown tilt domain stripes. The tilt domains, associated with higher energy (010) vertical twin walls, displayed different nanostructural responses based on the poling orientation. Specifically, an electric field applied perpendicular to the as-grown domain stripe allowed the domain tilts and associated vertical twin walls to persist. The result demonstrates that thin film ferroelectric devices can be designed to maintain unexpected domain morphologies in working poled environments.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any infermation, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Rcfercncc herein to any specific commercial product, process, or service by trade name, trademark, manulacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. 'The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Govcrnmen;. or any agency thereof.

Processes occurring within reactor cores are not amenable to direct experimental observation. Among major concerns are damage, fission gas accumulation and reaction between the fuel and its cladding all of which lead to swelling. These questions can be investigated through simulation with ion beams. As an example, we discuss the irradiation driven interaction of uranium–molybdenum alloys, intended for use as low-enrichment reactor fuels, with aluminum, which is used as fuel cladding. Uranium–molybdenum coated with a 100nm thin film of aluminum was irradiated with 3MeV Kr ions to simulate fission fragment damage. Mixing and diffusion of aluminum was followed as a function of irradiation with RBS and nuclear reaction analysis using the 27Al(p,γ)28Si reaction which occurs at a proton energy of 991.9keV. During irradiation at 150°C, aluminum diffused into the uranium alloy at a irradiation driven diffusion rate of 30nm2/dpa. At a dose of 90dpa, uranium diffusion into the aluminum layer resulted in formation of an aluminide phase at the initial interface. The thickness of this phase grew until it consumed the aluminum layer. The rapid diffusion of Al into these reactor fuels may offer explanation of the observation that porosity is not observed in the fuel particles but on their periphery.

Adsorbed on a solid surface, a molecule can migrate and carry an electric dipole moment. A nonuniform electric field can direct the motion of the molecule. A collection of the same molecules may aggregate into a monolayer island on the solid surface. Place such molecules on a dielectric substrate surface, beneath which an array of electrodes is buried. By varying the voltages of the electrodes individually, it is possible to program molecular patterning, direct an island to move in a desired trajectory, or merge several islands into a larger one. The dexterity may lead to new technologies, such as reconfigurable molecular patterning and programmable molecular cars. This paper develops a phase field model to simulate the molecular motion and patterning under the combined actions of dipole moments, intermolecular forces, entropy, and electrodes. Slides of this talk will be available at www.deas.harvard.edu/suo Z. Suo and W. Hong, PNAS 101, 7874 (2004). Y.F. Gao and Z. Suo, J. Appl. Phy. 93,4276 (2003). W. Lu and Z. Suo, J. Mech. Phys. Solids, 49, 1937 (2001). 2:30 PM *KK2.3/JJ2.3/U2.3 The Quasicontinuum Monte Carlo method for simulating surface growth. Leonard M. Sander l , Jason Devita l and Peter Smereka2; lphysics, University of Michigan, Ann Arbor, Michigan; 2Mathematics, University of Michigan, Ann Arbor, Michigan. We have developed an algorithm for treating growth on surfaces which treats the adatoms as a continuous fluid, and the islands and steps as

Adsorbed on a solid surface, a molecule can migrate and carry an electric dipole moment. A nonuniform electric field can direct the motion of the molecule. A collection of the same molecules may aggregate into a monolayer island on the solid surface. Place such molecules on a dielectric substrate surface, beneath which an array of electrodes is buried. By varying the voltages of the electrodes individually, it is possible to program molecular patterning, direct an island to move in a desired trajectory, or merge several islands into a larger one. The dexterity may lead to new technologies, such as reconfigurable molecular patterning and programmable molecular cars. This paper develops a phase field model to simulate the molecular motion and patterning under the combined actions of dipole moments, intermolecular forces, entropy, and electrodes. Slides of this talk will be available at www.deas.harvard.edu/suo Z. Suo and W. Hong, PNAS 101, 7874 (2004). Y.F. Gao and Z. Suo, J. Appl. Phy. 93,4276 (2003). W. Lu and Z. Suo, J. Mech. Phys. Solids, 49, 1937 (2001). 2:30 PM *JJ2.3/KK2.3/U2.3 The Quasicontinuum Monte Carlo method for simulating surface growth. Leonard M. Sander l , Jason Devita l and Peter Smereka2; lphysics, University of Michigan, Ann Arbor, Michigan; 2Mathematics, University of Michigan, Ann Arbor, Michigan. We have developed an algorithm for treating growth on surfaces which treats the adatoms as a continuous fluid, and the islands and steps as

[Co4/Pt10]n multilayers with strong out-of-plane magnetic anisotropy were fabricated by magnetron sputtering for Pt and e-beam deposition for Co on a Si/SiO2 substrate with a 100 Å Pt buffer layer in UHV. The patterning of submicron periodic arrays was done using 30 keV He ion implantation. The technique provides an excellent opportunity for precise tuning of the switching field in 'implantation patterned' Co/Pt by controlling the distance between irradiated areas and by controlling the irradiation dose. The results of systematic characterization of arrays for different doses ranging from 1015 to 5×1016 ions/cm are presented

We have investigated the structural and electrical characteristics of (BaxSr1−x)Ti1+yO3+z (BST) thin films. The BST thin films were deposited at 650°C on platinized silicon with good thickness and composition uniformity using a large area, vertical liquid-delivery metalorganic chemical vapor deposition (MOCVD) system. The (Ba+Sr)/Ti ratio of the BST films was varied from 0.96 to 1.05 at a fixed Ba/Sr ratio of 70/30, as determined using x-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). Patterned Pt top electrodes were deposited onto the BST films at 350°C through a shadow mask using electron beam evaporation. Annealing the entire capacitor structure in air at 700°C after deposition of top electrodes resulted in a substantial reduction of the dielectric loss. Useful dielectric tunability as high as 2.3:1 was measured.

We have investigated the structural and electrical characteristics of (BaXSrl,X)Til+YO~+Z (BST) thin films. The BST thin films were deposited at 650°C on platinized .sIhcon with good thickness and composition uniformity using a large area, vertical liquid-delivery metalorganic chemical vapor deposition (MOCVD) system. The (Ba+Sr)/Ti ratio of the BST films was varied from 0.96 to 1.05 at a fixed Ba/Sr ratio of 70/30, as determined using x-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). Patterned Pt top electrodes were deposited onto the BST films at 350”C through a shadow mask using electron beam evaporation. Annealing the entire capacitor structure in air at 700”C after deposition of top electrodes resulted in a substantial reduction of the dielectric loss. Useful dielectric tunability as high as 2.3:1 was measured. INTRODUCTION Nonlinear dielectrics such as barium strontium titanate (13ST) exhibit a large variation in permittivity, e, as a function of changes in the electric field applied to the material. For this reason, BST is a suitable candidate for high-frequency tunable phaseshifters [1-4]. To optimize the performance of such devices it is critical to maximize the dielectric tunability, i.e., the ratio of the permittivity at zero field to the permittivity at a defined field, and minimize the dielectric loss (tan 5) in the device operational frequency range. Fabrication of BST thin film devices by metalorganic chemical vapor deposition (NIOCVD) provides high compositional control, superior thickness and composition uniformity, high deposition rates, excellent conformality for films grown on high-aspect ratio structures, and the ability to scale film growth to large area substrates. EXPERIMENTAL APPROACH Bal.XSrXTil+YO~+Z thin films were synthesized using a large area vertical MOCVD system. A schematic diagram of the deposition system is shown in Fig. 1. Metalorganic precursors of Ba(thd)z, Sr(thd)z, and Ti (O-iPr)z-(thd)z with polyamme adducts were introduced using high purity nitrogen as a carrier gas into the MOCVD reactor, via a temperature-controlled flash-vaporizer and a computer-controlled liquid deliveq system (ATMI LDS-300B) that provides good composition control and reproducibility of the delivered precursor mixture. The temperature of the delivery lines was carefully controlled to avoid condensation or premature reaction of the precursors prior to introduction into the MOCVD reactor. The precursors were thoroughly mixed with high purity reactive gases (0, and Nz) in a showerhead designed to provide deposition of BST films with uniform composition and thickness over large area substrates. Table I summarizes the film deposition and processing conditions.

A combination of methods has been used to study the dynamic properties of a nanocomposite consisting of evaporated gold particles embedded in poly(tert-butyl acrylate). Rutherford backscattering spectrometry was used to measure the diffusion coefficients of the gold particles and of the polymer molecules; dewetting experiments were used to probe the viscosity of thin films with and without gold particles. The gold particles diffused with a temperature dependence similar to the temperature dependence of the polymer viscosity, but with hydrodynamic radii that greatly exceeded the actual radii of the gold particles. The gold particles also increased the viscosity of a low molecular weight polymer film by a factor of 4. Our interpretation of these results is that long-lived polymer bridges between individual gold particles stabilize clusters with dimensions of approximately 50 nm. A geometrical model of the bridging process was also developed. Results from this model can readily be applied to homogeneous nanoparticle dispersions in polymeric matrixes.