Effects of radiation damage on the critical resolved shear stresses in zirconium alloys for nuclear applications

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The effect of Sn concentration on oxide texture and microstructure formation in zirconium alloys

AbstractThe development of oxide texture and microstructure formed on two zirconium alloys with differing Sn contents (Zr–1Nb–1Sn–0.1Fe, i.e. ZIRLO™ and Zr–1.0Nb–0.1Fe) has been investigated using transmission Kikuchi diffraction (TKD) in the scanning electron microscope (SEM) and automated crystal orientation mapping in the transmission electron microscope (TEM). Bulk texture measurements were also performed using electron backscatter diffraction (EBSD) in order to quantify and compare the oxide macrotexture development. The Sn-free alloy showed significantly improved corrosion performance by delay of the transition region and reduced levels of hydrogen pickup. The macroscopic texture and grain misorientation analysis of the oxide films showed that the improved corrosion performance and reduced hydrogen pick up can be correlated with increased oxide texture strength, the improved oxide grain alignment resulting in longer, more protective columnar grain growth. A lower tetragonal phase fraction is also observed in the Sn-free alloy. This results in less transformation to the stable monoclinic phase during oxide growth, which leads to reduced cracking and interconnected porosity and also to the formation of larger, well-aligned monoclinic grains. It is concluded that the Zr–1.0Nb–0.1Fe alloy is more resistant to hydrogen pickup due the formation of a denser oxide with a larger columnar grain structure

Electrical, photoelectrical and morphological properties of ZnO nanowire networks grown on SiO2 and on Si

ZnO nanofibre networks (NFNs) were grown by vapour transport method on Si-based substrates. One type of substrate was SiO2 thermally grown on Si and another consisted of a Si wafer onto which Si nanowires (NWs) had been grown having Au nanoparticles catalysts. The ZnO-NFN morphology was observed by scanning electron microscopy on samples grown at 600 °C and 720 °C substrate temperature, while an focused ion beam was used to study the ZnO NFN/Si NWs/Si and ZnO NFN/SiO2 interfaces. Photoluminescence, electrical conductance and photoconductance of ZnO-NFN was studied for the sample grown on SiO2. The photoluminescence spectra show strong peaks due to exciton recombination and lattice defects. The ZnO-NFN presents quasi-persistent photoconductivity effects and ohmic I-V characteristics which become nonlinear and hysteretic as the applied voltage is increased. The electrical conductance as a function of temperature can be described by a modified three dimensional variable hopping model with nanometer-ranged typical hopping distances

Manufacture of electrical and magnetic graded and anisotropic materials for novel manipulations of microwaves

Spatial transformations (ST) provide a design framework to generate a required spatial distribution of electrical and magnetic properties of materials to effect manipulations of electromagnetic waves. To obtain the electromagnetic properties required by these designs, the most common materials approach has involved periodic arrays of metal-containing subwavelength elements. While aspects of ST theory have been confirmed using these structures, they are often disadvantaged by narrowband operation, high losses and difficulties in implementation. An all-dielectric approach involves weaker interactions with applied fields, but may offer more flexibility for practical implementation. This paper investigates manufacturing approaches to produce composite materials that may be conveniently arranged spatially, according to ST-based designs. A key aim is to highlight the limitations and possibilities of various manufacturing approaches, to constrain designs to those that may be achievable. The article focuses on polymer-based nano- and microcomposites in which interactions with microwaves are achieved by loading the polymers with high-permittivity and high-permeability particles, and manufacturing approaches based on spray deposition, extrusion, casting and additive manufacture

High resolution 3D chemical characterisation of a cadmium telluride solar cell by dynamic SIMS

Impurity elements such as chlorine and sulphur can have significant effects on the electrical performance of cadmium telluride (CdTe) solar cells. Here, the 3D distribution of such elements in a cadmium chloride treated CdTe device has been determined by high resolution dynamic SIMS, a novel technique that has not been applied to thin-film PV cells. It is found that as well as segregating to grain boundaries following treatment, chlorine also segregates to the CdS/CdTe interface. Conversely, sulphur shows a U-shaped diffusion profile. These results have potential implications for the processing thin-film CdTe devices

Initiation of dendritic failure of LLZTO via sub-surface lithium deposition

The occurrence of lithium deposition in occluded spaces within ceramic electrolytes due to electronic leakage currents can jeopardise the commercialization of power-dense solid-state batteries. Here, we utilize plasma-FIB serial sectioning to visualize the surface and sub-surface of a garnet solid electrolyte (LLZTO) after lithium plating. We study the morphology of surface spallation cracks, which represent the initial stage of dendrite formation. Employing a LiMg anode, we track the magnesium diffusion around these surface cracks with EDS. The absence of magnesium in early-stage cracks suggests they form due to the pressure build-up from the deposition of pure lithium in occluded pores near the electrolyte surface. These spallation cracks act as current focusing and stress concentration hot spots. Electron beam induced current imaging demonstrates that short-circuiting lithium dendrites grow from the spallations during plating. Thus, the sub-surface deposition of lithium is a possible explanation for the initiation of lithium dendrites in LLZTO

The effect of temperature on bubble lattice formation in copper under in situ He ion irradiation

In situ ion irradiation in a transmission electron microscope was used to investigate the effects of temperature on radiation-induced bubble lattice formation in Cu by low energy (12 keV) helium ions. Bubble lattices were observed to form between − 100 and 100 °C, but at 200 °C lattice formation was impeded by continued growth and agglomeration of bubbles. Both nucleation of bubbles, and to a lesser extent bubble lattice formation, are observed at lower fluences as temperature increases, which we suggest is due to increased point defect mobility. Previous work on point defect concentrations in irradiated copper is considered when interpreting these results

Revealing the role of fluoride‐rich battery electrode interphases by operando transmission electron microscopy

The solid electrolyte interphase (SEI), a complex layer that forms over the surface of electrodes exposed to battery electrolyte, has a central influence on the structural evolution of the electrode during battery operation. For lithium metallic anodes, tailoring this SEI is regarded as one of the most effective avenues for ensuring consistent cycling behavior, and thus practical efficiencies. While fluoride-rich interphases in particular seem beneficial, how they alter the structural dynamics of lithium plating and stripping to promote efficiency remains only partly understood. Here, operando liquid-cell transmission electron microscopy is used to investigate the nanoscale structural evolution of lithium electrodeposition and dissolution at the electrode surface across fluoride-poor and fluoride-rich interphases. The in situ imaging of lithium cycling reveals that a fluoride-rich SEI yields a denser Li structure that is particularly amenable to uniform stripping, thus suppressing lithium detachment and isolation. By combination with quantitative composition analysis via mass spectrometry, it is identified that the fluoride-rich SEI suppresses overall lithium loss through drastically reducing the quantity of dead Li formation and preventing electrolyte decomposition. These findings highlight the importance of appropriately tailoring the SEI for facilitating consistent and uniform lithium dissolution, and its potent role in governing the plated lithium's structure