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From Zn-Al LDH to ZIF-8@Zn-Al LDH conversion coatings on the surface of AA2024 alloy: Inside the process and the effect of the transformation on the protective properties
No full textNowadays, interest in metal organic frameworks (MOFs) as potential materials for corrosion protection of aluminium alloys is increasing. However, application of MOFs in the form of conversion coatings remains limited due to challenging process of MOFs growth directly on Al based surfaces. This obstacle can be overcome by surface pretreatment that promotes further MOF formation. In the current investigation, Zn-Al LDH (layered double hydroxide) grown on the surface of AA2024 aluminium alloy was recrystallised into ZIF-8@Zn-Al LDH coating. In situ synchrotron and ex situ XRD analyses showed that recrystallisation of Zn-Al LDH into ZIF-8 was accompanied by intercalation of 2-methylimidazolate into the LDH gallery under the applied treatment conditions. Such a complex structure of the coating was beneficial for the corrosion protection of AA2024 alloy as the obtained coating contained an increased amount of 2-methylimidazole inhibitive species. Moreover, it was found that the variation of the treatment condition (95–140 °C, 3–24 h) affected the final performance of the ZIF-8@Zn-Al-LDH coating and the coating obtained at 95 °C for 12 h demonstrated the best performance
Structural differences between single crystalline and polycrystalline NiMnGa-based alloys
No full textThree different martensitic crystal structures i.e. 10M, 14M, and NM of NiMnGa-based alloys, occurring indifferent forms, such as powders, polycrystalline melt-spun ribbons, and bulk single crystals were characterizedin detail. The crystal structure of materials having the same chemical compositions and martensitic structures butexisting in different forms were evaluated using high-energy synchrotron radiation, showing significant changesin lattice parameters. Additionally, the samples examined by high-resolution TEM imaging and electrondiffraction showed local structure changes including variations of stacking fault sequence, and lattice distortionat the grain and twin boundaries. The changes in lattice parameters of unit cells as well as the intensity ofmodulation reflections have been discussed in terms of microstructure (single variant, multivariant state), internalstresses, dislocation density, atomic shuffling, periodic and partially periodic atom displacements.Moreover, the effect of heat treatment on microstrain level, dislocation density, and formation of martensiticstructures was investigated
Uncertainty and worst-case expectation analysis for multiphysics QPR simulations
No full textQuadrupole resonators (QPRs) serve to characterize superconducting samples. Like any cavity, during operation, they will deviate from the design geometry for various reasons. Those deviations can be static, stemming from manufacturing variations reflected in the manufacturing tolerances, or dynamic, such as electromagnetic radiation pressure (Lorentz detuning) or microphonics. As a result, a QPR's measurement accuracy and general operation can be severely limited. In particular, during operation, it became evident that the third operating mode of typical QPRs is mainly affected. In this work, by solving the underlying multiphysics problem with random input parameters, we predict the predominant sources of significant measurement bias in surface resistance. On the one hand, we employ the stochastic collocation method compound with the polynomial chaos expansion (PC-SCM) to quantify uncertainties in the physical model governed by a coupled electro-stress-heat problem. On the other hand, we explore the perturbation analysis to calculate the mean-worst-scenario bound of the merit functions due to the first-order truncation of the Taylor expansion around mean parameter values. The developed method allows us to study the effect of a small nonlinear deformation on the performance of the QPR. Finally, we discuss the simulation results and their implication for the operational conditions of the QPRs
Driving factors for the peculiar bond length dependence and tetragonal distortion of and other chalcopyrites
No full textThe chalcopyrite alloy (Ag,Cu)(In,Ga)Se2 is a highly efficient thin film solar cell absorber, reaching record efficiencies above 23%. Recently, a peculiar behavior in the bond length dependence of (Ag,Cu)GaSe2 was experimentally proven. The common cation bond length, namely Ga–Se, decreases with increasing Ag/(Ag + Cu) ratio even though the crystal lattice expands. This is opposite to the behavior observed for Cu(In,Ga)Se2, where all bond lengths increase with increasing lattice size. To better understand this peculiar bond length behavior, element-specific bond lengths of (Ag,Cu)InSe2 and Ag(In,Ga)Se2 alloys are determined using extended x-ray absorption fine structure spectroscopy. They show that the peculiar bond length dependence occurs only for (Ag,Cu) alloys, independent of the species of common cation (In or Ga). The bond lengths are used to determine the anion displacements and to estimate their contribution to the bandgap bowing. Again, both behaviors differ significantly depending on the type of alloyed cation. A valence force field approach, relaxing bond lengths and bond angles, is used to describe the structural distortion energy for a comprehensive set of I–III–VI2 and II–IV–V2 chalcopyrites. The model reveals bond angle distortions as main driving factor for the tetragonal distortion and reproduces the literature values with less than 10% deviation. In contrast, the peculiar bond length dependence is not reproduced, demonstrating that it originates from electronic effects beyond the scope of this structural model. Thus, a fundamental understanding of bond length behavior and tetragonal distortion is achieved for chalcopyrite materials, benefiting their technological applications such as high efficiency thin film photovoltaics
Effect of cyclic loading on microstructure and plastic deformation in heat-treated Co–28Cr–6Mo alloy fabricated via laser powder bed fusion: An in situ synchrotron X-ray diffraction study
No full textWe present a systematic microstructure-oriented plasticity investigation of an additively manufactured cobaltbasedalloy aiming to relate microstructural changes to the fatigue resistance. A load-controlled cyclic test inthe low-cycle fatigue regime was utilized to study mechanical response and microstructural changes in the alloyafter reverse phase transformation heat treatment. Deformation-induced FCC → HCP phase transformation wasfollowed using in situ synchrotron X-ray diffraction combined with ex situ electron backscatter diffraction andscanning electron microscopy. Scanning transmission electron microscopy provided experimental evidence of thepresence of precipitates in the solution annealed sample. It was found, that a stepwise increase in plasticdeformation is attributed to nucleation and growth of different martensitic crystallographic variants. These insightsinto plasticity and microstructural changes suggest that the reverse phase transformation heat treatment isan effective approach for improving the fatigue resistance of low stacking fault energy alloys, that are susceptibleto deformation-induced martensitic transformation
Charge-Density-Wave Control by Adatom Manipulation and Its Effect on Magnetic Nanostructures
No full textCharge-density waves (CDWs) are correlated states of matter, in which the electronic density is modulated periodically due to electronic and phononic interactions. Often, CDW phases coexist with other correlated states, such as superconductivity, spin-density waves, or Mott insulators. Controlling CDW phases may, therefore, enable the manipulation of the energy landscape of these interacting states. The transition metal dichalcogenide 2H-NbSe hosts both CDW order and superconductivity, with the incommensurate CDW phase resulting in different CDW-to-lattice alignments at the atomic scale. Using scanning tunneling microscopy, we position adatoms on the surface to induce reversible CDW domain switching. We show that the domain structure critically affects other local interactions, particularly the hybridization of Yu–Shiba–Rusinov states, which emerge from exchange interactions of magnetic Fe atoms with the superconductor. Our results suggest that CDW manipulation could also be used to introduce domain walls into coupled spin chains on superconductors, potentially impacting topological superconductivity
Evolution of Magnetic Properties with Structure and Morphology of Co/Alq Bilayer: A Thickness Dependent Study
No full textOrganic spintronics (OS), which focuses on utilizing the spin degree of freedom in organic materials, has been a fascinating topic because of its technological aspects and future applications. In-plane uniaxial magnetic anisotropy (UMA) is becoming increasingly important in the rapidly developing field of OS. In this study, Cobalt (Co) films were deposited with varying thicknesses on the Tris (8-hydroxyquinolinato) aluminium (Alq) layer to investigate the evolution of magnetism and UMA. Magnetic measurements and simultaneous domain imaging have been done using the magneto-optic Kerr effect by varying the azimuthal angle between the easy axis of magnetization and the applied magnetic field. It was discovered that the bilayer exhibits a well-defined UMA in the film plane upon forming a continuous Co film with a thickness of around 10 nm. Structural and morphological properties of all the Co/Alq3 bilayers were studied using grazing-incidence small-angle X-ray scattering and wide-angle X-ray scattering measurements at synchrotron radiation source, P03 beamline PETRA-III, Germany. The combined analysis revealed that in contrast to the inorganic magnetic polycrystalline thin films, where the UMA originates mainly due to the stress, the origin of UMA in Co/Alq is attributed to the magnetocrystalline anisotropy caused by c-axis (Co (002)) preferential orientation. The surface free energy of Alq is less than that of Co; therefore, the growth of Co starts with island formation, which coalescences with increasing thickness. The observed structure orientation may be attributed to minimizing the magnetoelastic energies due to coalescence known as the zipping effect. The absence of UMA in films with lower thickness film (~5 nm) is understood in terms of random short-range stress caused by isotropic pinning due to the diffused interface
In-Depth Analysis of the Species and Transformations during Sol Gel-Assisted VPC Synthesis
No full textThe sol–gel reaction mechanism of 211 MAX phases has proven to be very complex when identifying the intermediate species, chemical processes, and conversions that occur from a mixture of metal salts and gelling agent into a crystalline ternary carbide. With mostly qualitative results in the literature (CrGaC, CrGeC, and VGeC), additional analytical techniques, including thermal analysis, powder diffraction, total scattering, and various spectroscopic methods, are necessary to unravel the identity of the chemical compounds and transformations during the reaction. Here, we demonstrate the combination of these techniques to understand the details of the sol–gel synthesis of MAX phase VPC. The metal phosphate complexes, as well as amorphous/nanocrystalline vanadium phosphate species (V in different oxidation states), are identified at all stages of the reaction and a full schematic of the reaction process is suggested. The early amorphous vanadium species undergo multiple changes of oxidation states while organic species decompose releasing a variety of small molecule gases. Amorphous oxides, analogous to [NH][VO][HPO], VPO4O, and VOPO are identified in the dried gel obtained during the early stages of the heating process (300 and 600 °C), respectively. They are carbothermally reduced starting at 900 °C and subsequently react to crystalline VPC with the excess carbon in the reaction mixture. Through CHN analysis, we obtain an estimate of left-over amorphous carbon in the product which will guide future efforts of minimizing the amount of carbon in sol gel-produced MAX phases which is important for subsequent property studies
Formation Mechanism and Hydrothermal Synthesis of Highly Active Ir RuO Nanoparticles for the Oxygen Evolution Reaction
No full textIridium dioxide (IrO2), ruthenium dioxide (RuO2), and their solid solutions (Ir1–xRuxO2) are very active electrocatalysts for the oxygen evolution reaction (OER). Efficient and facile synthesis of nanosized crystallites of these materials is of high significance for electrocatalytic applications for converting green energy to fuels (power-to-X). Here, we use in situ X-ray scattering to examine reaction conditions for different Ir and Ru precursors resulting in the development of a simple hydrothermal synthesis route using IrCl3 and KRuO4 to obtain homogeneous phase-pure Ir1–xRuxO2 nanocrystals. The solid solution nanocrystals can be obtained with a tunable composition of 0.2 < x < 1.0 and with ultra-small coherently scattering crystalline domains estimated from 1.3 to 2.6 nm in diameter based on PDF refinements. The in situ X-ray scattering data reveal a two-step formation mechanism, which involves the initial loss of chloride ligands followed by the formation of metal–oxygen octahedra clusters containing both Ir and Ru. These octahedra assemble with time resulting in long-range order resembling the rutile structure. The mixing of the metals on the atomic scale during the crystal formation presumably allows the formation of the solid solution rather than heterogeneous mixtures. The size of the final nanocrystals can be controlled by tuning the synthesis temperature. The facile hydrothermal synthesis route provides ultra-small nanoparticles with activity toward the OER in acidic electrolytes comparable to the best in the literature, and the optimal material composition very favorably combines low overpotential, high mass activity, and increased stability
A hybrid method integrating Green’s function Monte Carlo and projected entangled pair states
No full textThis paper introduces a hybrid approach combining Green's function Monte Carlo (GFMC) method with projected entangled pair state (PEPS) ansatz. This hybrid method regards PEPS as a trial state and a guiding wave function in GFMC. By leveraging PEPS's proficiency in capturing quantum state entanglement and GFMC's efficient parallel architecture, the hybrid method is well-suited for the accurate and efficient treatment of frustrated quantum spin systems. As a benchmark, we applied this approach to study the frustrated J–J Heisenberg model on a square lattice with periodic boundary conditions (PBCs). Compared with other numerical methods, our approach integrating PEPS and GFMC shows competitive accuracy in the performance of ground-state energy. This paper provides systematic and comprehensive discussion of the approach of our previous work [Phys. Rev. B 109 235133 (2024)]