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Study of room-temperature deposited ZrN thin films
No full textZirconium nitride (ZrN) has attracted scientific interest due to its diverse physical and functional properties. Despite the energetic favourability of room-temperature synthesis of ZrN, only a handful attempts have been made to understand the low-temperature synthesis protocols. In the present work, we synthesized a series of Zr–N thin films by varying partial N gas flow (RN) at room temperature (300 K). The structural and compositional characteristics of resulting Zr–N films were studied. The investigation combines X-ray reflectivity (XRR), X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) measurements, which includes X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and variable angle spectroscopic ellipsometer (VASE). XRR results reveal the effects of varying RN on deposition rate, providing insights into the formation of ZrN phase. XRD patterns reveal the structural evolution from the hcp Zr to fcc ZrN phase. Further, structural parameters, including lattice parameter and crystallite size are systematically examined, revealing high-quality nature of the films, with optimal results observed in RN2 = 5–10% samples. XAFS measurements, particularly XANES of N and Zr K-edges, provide insights into the local environment, showing a centrosymmetric structure with octahedral symmetry within the ZrN films. Shifting of pre-edge features in the XANES spectra suggests variations in the oxidation state, implying a complex interplay between Zr and N atoms within the films. Emphasizing the importance of EXAFS, this study showcases its reliability for quantitative analyses. The technique unravels atomic coordination and bond lengths within the Zr–N films, which is crucial for a comprehensive understanding of the film’s structural characteristics. VASE measurement was done to understand the optical behaviour from the real and imaginary parts of permittivity spectra
SPA-LEED studies on the growth morphology of ultra-thin FeO films on SrTiO (001)
No full textUltrathin FeO films were successively grown on SrTiO(001) by reactive molecular beam epitaxy at different growth temperatures. Surface sensitive spot profile analysis low energy electron diffraction (SPA-LEED) was used to characterise the surface morphology and structural information after each deposition step. For very low coverages () an initial growth-phase was found, which can be assigned to (111)-oriented FeO. After this growth phase, the films continue to grow up to a film thickness of in a FeO rock salt structure or have a strongly disordered FeO structure. Subsequently, a well-ordered FeO(001) spinel structure is formed. Independent of the deposition temperature, defect density decreases with increasing film thickness, while crystallinity, i.e. structural quality, of the magnetite thin films increases with both increasing film thickness and increasing deposition temperature. The results show that mosaics and domains/grains can be found on the surface. Higher deposition temperatures do not cause any change in the mosaic spread angle but the mean domain size increases
Dissimilar laser welding of an as-rolled CoCrFeMnNi high entropy alloy to Inconel 718 superalloy
No full textIn this work, dissimilar laser welding between an as-rolled CoCrFeMnNi high entropy alloy (HEA) and Inconel718 Ni-base superalloy was successfully performed. Defect-free joints with a tensile strength of 822 MPa and afracture strain of 7.1 % were obtained. The microstructural analysis was conducted using scanning electronmicroscopy (SEM), electron backscattered diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDS) andhigh energy synchrotron X-ray diffraction (SXRD), complemented by thermodynamic calculations using theCalPhaD methodology. Mechanical assessment of the joints was conducted via microhardness mapping andtensile testing, allowing to unveil processing-microstructure-properties relationships. Although the precipitationof the Laves phase was identified within the fusion zone, our results reveal the excellent dissimilar weldabilitybetween the two alloys, allowing the deployment of this dissimilar material pair for structural applications
Coupled study on in-situ synchrotron high-energy X-ray diffraction and in-situ EBSD on the interfacial stress gradient in layered metals
No full textAs one of the heterostructures, the layered structure has attracted extensive research interest as it achieves superior properties to individual components. The layer interface is considered a critical factor in determining the mechanical properties of layered metals, where heterogeneity across the interface results in the strengthening of the soft layer and forming an interfacial stress gradient in the hard layer. However, there is still limited research associated with the formation of interfacial stress gradients in the hard layer, as stress measurement at high spatial resolution remains technically challenging. In the present study, we experimentally quantified the formation of interfacial stress gradients in the Ti layer of Ti/Al layered metal upon tension using in-situ high-energy X-ray diffraction (XRD). The analysis coupling in-situ high-energy XRD and in-situ electron back-scattered diffraction (EBSD) suggested that the interfacial stress gradient in the Ti layer rapidly rose as the Al layer was insufficient to accommodate the deformation of Ti. During the later deformation stage, collective effects of dislocation motion and geometrically necessary dislocation (GND) accumulation in the Al layer determined the evolution of interfacial stress gradients. The maximum interfacial stress gradient is below 0.4 MPa/μm in Ti layers, with a constant range width of 35 μm independent of the macroscopic strain. The present study therefore opens a new window to local stress modification using incompatible component deformation, which is instructive for the design and fabrication of high-performance layered metals
Exploring optimal Li composite electrode anodes for lithium metal batteries through in situ X-ray computed tomography
No full textThe uncontrolled Li dissolution/deposition dynamics and rapid Li pulverizations hinder the widespread deployment of Li metal batteries (LMB). Designing a Li composite electrode possessing a mechanically robust and lithiophilic three-dimensional (3D) framework represents a promising strategy to address these challenges. This study involves the preparation of three uniquely tailored Li-B-Mg composites using a combined metallurgical process of melting, casting, and rolling, along with the synergistic application of in situ X-ray computed tomography (CT) and post-mortem failure analysis to explore the most promising composite electrode candidate for LMBs. During the in-depth investigation, the optimal 70Li-B-Mg composite electrode stands out due to its robust skeleton fiber structure, uniform Li dissolution/deposition characteristics and high capacity of free-Li. Its promising prospects for enabling high-performance LMBs are showcased by the superior performance of the built Li||O2, Li||LiFePO, Li||NCM622 and Li||NCM811 battery systems. This work offers a novel approach for exploring universally applicable and robust Li composite electrodes to realize high-performance LMBs using in situ CT analysis
Multiscale characterization of NiTi shape memory alloy to Ti6Al4V dissimilar laser welded joints: Reasons for inherent brittleness
No full textDissimilar joining of advanced engineering alloys is of major importance for several applications to takeadvantage of the properties of each one of the base materials. Due to the formation of Ti2Ni and to the thermalexpansion coefficient mismatch, dissimilar laser welding between Ti6Al4V and NiTi is particularly challenging.Nevertheless, a joint without pores or cracks was obtained using a Nd:YAG laser system with a wavelength of1064 nm and a spot size of 0.45 mm. Full-penetration occurred and the weld pool is asymmetric with a key-holeshape. Typical dendritic structure is observed throughout the welded zone, although without apparent orientationon the middle. Close to the Ti6Al4V side a zone with a different morphology is observed along the entirethickness with high hardness corresponding to NiTi2 . Multiscale microstructure and mechanical characterizationencompassing electron microscopy, synchrotron X-ray diffraction, electron probe microanalysis and instrumentednanoindentation were used to reveal the microstructure/properties relationships correlating theextremely high hardness and brittleness of the welded joint to its microstructural constituent
Ultraviolet-C persistent luminescence and defect properties in CaAlSiO:Pr
No full textIn recent years, significant attention has been focused on the study of materials with ultraviolet (UV) persistent luminescence (PersL) due to their prospective application possibilities. Although novel UV persistent phosphors are being developed, reports on defect properties and PersL mechanisms are limited. In this study, the incorporation of Pr ions in CaAlSiO is analyzed using X-ray diffraction (XRD) and X-ray absorption techniques, whereas PersL properties are characterized by photoluminescence (PL), thermostimulated luminescence (TSL) and electron paramagnetic resonance (EPR) methods. Analysis of the Pr L-edge X-ray absorption spectra suggests that praseodymium atoms substitute for calcium atoms. The UV-C PersL of the host results from thermally assisted recombination of charge carriers with trap depths within the 0.50–0.87 eV range. Moreover, a partial correlation of PersL and TSL with the decay of X-ray-induced paramagnetic centers was observed. This study expands the knowledge base on the structure of CaAlSiO and establishes the optimal Pr concentration for efficient UV-C PersL
Resolving the pressure induced ‘self-insertion’ in skutterudite CoSb3
No full textCoSb3 belongs to the skutterudite family of compounds and serves as a crucial platform for the exploration of thermoelectric materials. Under compression it undergoes a ‘self-insertion’ isostructural transition resulting in a peculiar redistribution of large Sb atoms between different crystallographic sites. We conducted a comprehensive investigation of CoSb3 structural phase stability up to 70 GPa using single crystal material in the regimes of conventional single crystal X-ray diffraction and the X-ray scattering focused on measuring Bragg peak at high resolution (including elements of Bragg Coherent Diffraction Imaging). We explore the compression behavior of CoSb3 in three different pressure transmitting media (PTM) and address several important topics: influence of various PTMs and nonhydrostatic stresses on the strongly correlated system of CoSb3, including the ‘self-insertion’ crossover, phase stability of CoSb3, the compound’s polymorphism, its crystal chemistry, and its variation under pressure. Among other important observations, we track population of Sb atom within CoSb3 dodecahedral sites on compression, during the process of ‘self-insertion’, and on decompression. We detect that ‘self-insertion’ may not only reduce the compressibility, but also make it negative. Finally, but not the least, we report that the ‘self-insertion’ crossover is an important step preceding a previously unknown phase transformation from a cubic Im3 ̅ CoSb3 into a trigonal R3 ̅ occurring above 40 GPa, and discuss the distinctive behavior of CoSb3 phases and their structural frameworks
Meson thermalization with a hot medium in the open Schwinger model
No full textQuantum field theories treated as open quantum systems provide a crucial framework for studying realistic experimental scenarios, such as quarkonia traversing the quark-gluon plasma produced at the Large Hadron Collider. In such cases, capturing the complex thermalization process requires a detailed understanding of how particles evolve and interact with a hot medium. Considering the open lattice Schwinger model and using tensor network algorithms, we investigate the thermalization dynamics of mesonic particles in a hot medium, such as the Schwinger boson or the electric flux string. We simulate systems with up to 100 lattice sites, achieving accurate preservation of the electric field parity symmetry, demonstrating the algorithm's robustness and scalability. Our results reveal that the thermalization time increases with stronger dissipation from the environment, increasing environment temperature, higher background electric field and heavier fermion masses. Further, we study the quantum mutual information between the two halves of the flux string connecting a meson's constituent particles and analyze its relation to relevant dynamical observables
Renormalisation Group Equations for 2+1 clover fermions
No full textMany lattice QCD simulations now have many lattice spacings available, and it is of interest to investigate how they scale. In this talk we first derive renormalisation group equations appropriate for 2+1 clover fermions. This is then used together with pion mass and gradient flow results at five lattice spacings to study scaling