Scientific Output

Over 10.000 scientific papers have been published by members of the Materials Chain since the foundation of the University Alliance Ruhr in 2010. This tremendous output is proof of the excellent environment the Ruhr Area provides for research in the field of materials science and technology.

Below, you can either scroll through the complete list of our annually published material, or search for a specific author or term via the free text search to get to know our research strengths. You can also review the publication record of every Materials Chain member via his or her personal member’s page.

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  • 2024 • 29 Testing equivalence of multinomial distributions — A constrained bootstrap approach
    Bastian, P. and Dette, H. and Koletzko, L.
    Statistics and Probability Letters 206 (2024)
    In this paper we develop a novel bootstrap test for the comparison of two multinomial distributions. The two distributions are called equivalent or similar if a norm of the difference between the class probabilities is smaller than a given threshold. In contrast to most of the literature our approach does not require differentiability of the norm and is in particular applicable for the maximum- and L1-norm. © 2023 Elsevier B.V.
    view abstractdoi: 10.1016/j.spl.2023.109999
  • 2024 • 28 Comparing regression curves: an L 1-point of view
    Bastian, Patrick and Dette, Holger and Koletzko, Lukas and Möllenhoff, Kathrin
    Annals of the Institute of Statistical Mathematics 76 159 – 183 (2024)
    In this paper, we compare two regression curves by measuring their difference by the area between the two curves, represented by their L1 -distance. We develop asymptotic confidence intervals for this measure and statistical tests to investigate the similarity/equivalence of the two curves. Bootstrap methodology specifically designed for equivalence testing is developed to obtain procedures with good finite sample properties and its consistency is rigorously proved. The finite sample properties are investigated by means of a small simulation study. © 2023, The Institute of Statistical Mathematics, Tokyo.
    view abstractdoi: 10.1007/s10463-023-00880-8
  • 2024 • 27 Investigating the inflow into a granular bed using a locally resolved method
    Brömmer, M. and Scharnowski, M. and Illana Mahiques, E. and Wirtz, S. and Scherer, V.
    Particuology 85 89-101 (2024)
    doi: 10.1016/j.partic.2023.03.022
  • 2024 • 26 Sampling the Materials Space for Conventional Superconducting Compounds
    Cerqueira, Tiago F. T. and Sanna, Antonio and Marques, Miguel A. L.
    Advanced Materials 36 (2024)
    A large scale study of conventional superconducting materials using a machine-learning accelerated high-throughput workflow is performed, starting by creating a comprehensive dataset of around 7000 electron–phonon calculations performed with reasonable convergence parameters. This dataset is then used to train a robust machine learning model capable of predicting the electron–phonon and superconducting properties based on structural, compositional, and electronic ground-state properties. Using this machine, the transition temperatures (Tc) of approximately 200 000 metallic compounds are evaluated, all of which are on the convex hull of thermodynamic stability (or close to it) to maximize the probability of synthesizability. Compounds predicted to have Tc values exceeding 5 K are further validated using density-functional perturbation theory. As a result, 541 compounds with Tc values surpassing 10 K, encompassing a variety of crystal structures and chemical compositions, are identified. This work is complemented with a detailed examination of several interesting materials, including nitrides, hydrides, and intermetallic compounds. Particularly noteworthy is LiMoN2, which is predicted to be superconducting in the stoichiometric trigonal phase, with a Tc exceeding 38 K. LiMoN2 has previously been synthesized in this phase, further heightening its potential for practical applications. © 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/adma.202307085
  • 2024 • 25 Ni-Alloyed Copper Iodide Thin Films: Microstructural Features and Functional Performance
    Dethloff, Christiane and Thieme, Katrin and Selle, Susanne and Seifert, Michael and Vogt, Sofie and Splith, Daniel and Botti, Silvana and Grundmann, Marius and Lorenz, Michael
    Physica Status Solidi (B) Basic Research (2024)
    To tailor electrical properties of often degenerate pristine CuI, Ni is introduced as alloy constituent. Cosputtering in a reactive, but also in an inert atmosphere as well as pulsed laser deposition (PLD), is used to grow (Formula presented.) thin films. The Ni content within the alloy thin films is systematically varied for different growth techniques and growth conditions. A solubility limit is evidenced by an additional (Formula presented.) phase for Ni contents (Formula presented.), observed in X-Ray diffraction and atomic force microscopy by a change in surface morphology. Furthermore, metallic, nanoscaled nickel clusters, revealed by X-Ray photoelectron spectroscopy and high-resolution transmission electron microscopy (HRTEM), underpin a solubility limit of Ni in CuI. Although no reduction of charge carrier density is observed with increasing Ni content, a dilute magnetic behavior of the thin films is observed in vibrating sample magnetometry. Further, independent of the deposition technique, unique multilayer features are observed in HRTEM measurements for thin films of a cation composition of (Formula presented.). Opposite to previous claims, no transition to n-type behavior was observed, which was also confirmed by density functional theory calculations of the alloy system. © 2024 The Authors. physica status solidi (b) basic solid state physics published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/pssb.202300492
  • 2024 • 24 Statistical inference for function-on-function linear regression
    Dette, Holger and Tang, Jiajun
    Bernoulli 30 304 – 331 (2024)
    We propose a reproducing kernel Hilbert space approach for statistical inference regarding the slope in a function-on-function linear regression via penalised least squares, regularized by the thin-plate spline smoothness penalty. We derive a Bahadur expansion for the slope surface estimator and prove its weak convergence as a process in the space of all continuous functions. As a consequence of these results, we construct minimax optimal estimates, simultaneous confidence regions for the slope surface and simultaneous prediction bands. Moreover, we derive new tests for the hypothesis that the maximum deviation between the “true” slope surface and a given surface is less than or equal to a given threshold. In other words, we are not trying to test for exact equality (because in many applications this hypothesis is hard to justify), but rather for pre-specified deviations under the null hypothesis. To ensure practicability, non-standard bootstrap procedures are developed addressing particular features that arise in these testing problems. We also demonstrate that the new methods have good finite sample properties by means of a simulation study and illustrate their practicability by analyzing a data example. © 2024 ISI/BS.
    view abstractdoi: 10.3150/23-BEJ1598
  • 2024 • 23 Phase formation and electrical properties of reactively sputtered Fe1−x O thin films
    Evertz, S. and Nicolin, N. and Cheng, N. and Primetzhofer, D. and Best, J.P. and Dehm, G.
    Journal of Physics D: Applied Physics 57 (2024)
    Wüstite, Fe1−x O, is a crucial phase for the transition to CO2-free steel manufacturing as well as promising for electrochemical applications such as water splitting and ammonia synthesis. To study the effect of interfaces in these applications, thin-film model systems with defined interfaces are ideal. Previous studies lack a description of the growth mechanism to obtain Fe1−x O thin films. Here, we investigate the phase formation of metastable Fe1−x O during reactive magnetron sputtering while systematically varying the O2/Ar flow ratio from 1.8% to 7.2% and the pressure-distance product between 3.5 and 7.2 Pa cm. If bulk diffusion is minimized, thin films containing 96 vol.% wüstite and 4 vol.% Fe as impurity phase were achieved. Therefore, the wüstite phase formation appears to be surface diffusion dominated. To reveal the influence of impurity phases in wüstite on the electrical resistivity, systematic electrical resistivity measurements while cooling in situ were performed for the first time. The electrical resistivity was lower than that of single crystals of the respective iron oxides. This is attributed to the formation of Fe-rich layers at the substrate-film interface, which serve as additional conduction paths. © 2023 The Author(s). Published by IOP Publishing Ltd
    view abstractdoi: 10.1088/1361-6463/ad0a3e
  • 2024 • 22 Prediction of high- Tc superconductivity in ternary actinium beryllium hydrides at low pressure
    Gao, Kun and Cui, Wenwen and Shi, Jingming and Durajski, Artur P. and Hao, Jian and Botti, Silvana and Marques, Miguel A. L. and Li, Yinwei
    Physical Review B 109 (2024)
    Hydrogen-rich superconductors are promising candidates to achieve room-temperature superconductivity. However, the extreme pressures needed to stabilize these structures significantly limit their practical applications. An effective strategy to reduce the external pressure is to add a light element M that binds with H to form MHx units, acting as a chemical precompressor. We exemplify this idea by performing ab initio calculations of the Ac-Be-H phase diagram, proving that the metallization pressure of Ac-H binaries, for which critical temperatures as high as 200 K were predicted at 200 GPa, can be significantly reduced via beryllium incorporation. We identify three thermodynamically stable (AcBe2H10, AcBeH8, and AcBe2H14) and four metastable compounds (fcc AcBeH8, AcBeH10, AcBeH12 and AcBe2H16). All of them are superconductors. In particular, fcc AcBeH8 remains dynamically stable down to 10 GPa, where it exhibits a superconducting-transition temperature Tc of 181 K. The Be-H bonds are responsible for the exceptional properties of these ternary compounds and allow them to remain dynamically stable close to ambient pressure. Our results suggest that high-Tc superconductivity in hydrides is achievable at low pressure and may stimulate experimental synthesis of ternary hydrides. © 2024 American Physical Society.
    view abstractdoi: 10.1103/PhysRevB.109.014501
  • 2024 • 21 Comparing two IBM implementations for the simulation of uniform packed beds
    Gorges, C. and Brömmer, M. and Velten, C. and Wirtz, S. and Mahiques, E.I. and Scherer, V. and Zähringer, K. and van Wachem, B.
    Particuology 86 1-12 (2024)
    doi: 10.1016/j.partic.2023.04.006
  • 2024 • 20 pH-Dependent photocatalytic performance of faceted BiOBr semiconductor particles in degradation of dyes
    Guo, Yuxi and Siretanu, Igor and Mugele, Frieder and Mul, Guido and Mei, Bastian
    Molecular Catalysis 553 (2024)
    Bismuth oxyhalides, such as bismuth-oxy-bromide (BiOBr), show high performance in photocatalytic oxidation of water pollutants. Process conditions, and in particular the pH of the solution, largely affect the photocatalytic efficacy, which is fundamentally poorly understood. We prepared {001} faceted bismuth-oxy-bromide (BiOBr), and determined by advanced AFM analysis that the surface charge of the {001} facet of BiOBr is slightly positive at acidic pH (pH 3) and significantly negative and increasing in negative surface charge in the order pH 6 < pH 9. Decomposition of MB or RhB by illumination of BiOBr is strongly favored by basic conditions (pH 9-10), as evident from discoloration experiments, and determination of the TOC as a function of time of illumination. Reference experiments show the pH dependent degradation profiles cannot be explained by differences in quantities of adsorption of the dye, but rather by the lifetime and/or quantity of BiOBr related photoexcited (surface) charge carriers (holes and electrons) – correlating with surface charge. Using MeOH and other scavengers, we show oxidation of MB or RhB is mainly induced by superoxide anions (•O2− radicals) at low pH and by holes or hydroxyl radicals at high pH – in agreement with surface charge induced band bending. This study provides novel understanding of the pH dependence of the rates of photocatalytic degradation of dyes using BiOBr photocatalysts. © 2023
    view abstractdoi: 10.1016/j.mcat.2023.113753
  • 2024 • 19 Influence of pre-existing configurations of dislocations on the initial pop-in load during nanoindentation in a CrCoNi medium-entropy alloy
    Habiyaremye, Frederic and Guitton, Antoine and Chen, Xiaolei and Richeton, Thiebaud and Berbenni, Stéphane and Schäfer, Florian and Laplanche, Guillaume and Maloufi, Nabila
    Philosophical Magazine 104 137 – 160 (2024)
    The origin and mechanisms responsible for incipient plasticity in metals are still poorly understood. Moreover, the reasons for the recently reported large scattering of the initial pop-in load remain unclear. Hence, this study addresses these issues through a combination of nanoindentation tests and electron channelling contrast imaging characterisation considering a CrCoNi medium-entropy alloy. Experimental findings were also supported by elastic calculations that consider both the indentation and dislocation stress fields. A wide scatter in the maximum shear stress underneath the indenter, as expected, was observed for the analysis based on dislocation density. As a consequence, the spatial arrangement of dislocations within the indented region or local dislocation configuration is introduced as a new parameter to overcome overly simple analysis based on the dislocation density. The maximum shear stress underneath the indenter increased from 6 GPa for dislocation closer to the indentation axis to 11 GPa at 600 nm for dislocation far away from it. Additionally, elastic calculations revealed that the response to the incoming nanoindenter was different for dislocations with different configurations. Thus, the complex interactions of stress fields due to configurations of dislocations and indentation account for the large scatter of the maximum shear stress beneath the indenter. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
    view abstractdoi: 10.1080/14786435.2023.2290541
  • 2024 • 18 Spatially resolved investigation of flame particle interaction in a two dimensional model packed bed
    Khodsiani, M. and Namdar, R. and Varnik, F. and Beyrau, F. and Fond, B.
    Particuology 85 167-185 (2024)
    doi: 10.1016/j.partic.2023.03.011
  • 2024 • 17 On the inherent strength of Cr23C6 with the complex face-centered cubic D84 structure
    Kishida, Kyosuke and Ito, Mitsuhiro and Inui, Haruyuki and Heilmaier, Martin and Eggeler, Gunther
    Acta Materialia 263 (2024)
    The deformation behavior of single crystals of Cr23C6 with the complex D84 crystal structure based on the face-centered cubic lattice has been investigated by micropillar compression as a function of crystal orientation and specimen size at room temperature. For the first time, the {111}<1‾01> slip system is identified to be the only operative slip system. The 1/2<1‾01> dislocation dissociates into two partial dislocations with identical collinear Burgers vectors (b) as confirmed by transmission electron microscopy (TEM) and atomic-resolution scanning transmission electron microscopy (STEM). The energy of the stacking fault bounded by two coupled partial dislocations with the b = 1/4<1‾01> is evaluated from their separation distances to be 840 mJ/m2. The critical resolved shear stress (CRSS) for {111}<1‾01> slip increases with the decrease in the specimen size, following the inverse power-law relationship with a relatively low exponent of ∼ -0.19. The room-temperature bulk CRSS value evaluated by extrapolating this inverse relationship to the specimen size of 20∼30 μm is 0.79 ± 0.15 GPa. The exact position of the slip plane among many different parallel {111} atomic planes and possible dislocation dissociations on the relevant slip planes are discussed based on the calculated generalized stacking fault energy (GSFE) curves. The inter-block layer slip is deduced to occur for {111}<1‾01> slip based on the TEM/STEM observations and the result of GSFE calculations. Finally, plausible atomic structures for stacking faults on (111) and coherent twin boundaries are discussed. © 2023 Acta Materialia Inc.
    view abstractdoi: 10.1016/j.actamat.2023.119518
  • 2024 • 16 Numerical study of convective heat transfer in static arrangements of particles with arbitrary shapes: A monolithic hybrid lattice Boltzmann-finite difference-phase field solver
    Namdar, R. and Khodsiani, M. and Safari, H. and Neeraj, T. and Hosseini, S.A. and Beyrau, F. and Fond, B. and Thévenin, D. and Varnik, F.
    Particuology 85 186-197 (2024)
    doi: 10.1016/j.partic.2023.03.020
  • 2024 • 15 Investigating the platinum electrode surface during Kolbe electrolysis of acetic acid
    Olde Nordkamp, Margot and Ashraf, Talal and Altomare, Marco and Borca, Andrea Casanova and Ghigna, Paolo and Priamushko, Tatiana and Cherevko, Serhiy and Saveleva, Viktoriia A. and Atzori, Cesare and Minguzzi, Alessandro and He, X...
    Surfaces and Interfaces 44 (2024)
    Platinum is commonly applied as the anode material for Kolbe electrolysis of carboxylic acids thanks to its superior performance. Literature claims that the formation of a barrier layer on the Pt anode in carboxylic acid electrolyte suppresses the competing oxygen evolution and promotes anodic decarboxylation. In this work, we show by using a combination of complementary in situ and ex situ surface sensitive techniques, that the presence of acetate ions also prevents the formation of a passive oxide layer on the platinum surface at high anodic potentials even in aqueous electrolyte. Furthermore, Pt dissolves actively under these conditions, challenging the technical implementation of Kolbe electrolysis. Future studies exploring the activity-structure-stability relation of Pt are required to increase the economic viability of Kolbe electrolysis. © 2023 The Author(s)
    view abstractdoi: 10.1016/j.surfin.2023.103684
  • 2024 • 14 A simulation study for a cost-effective PET-like detector system intended to track particles in granular assemblies
    Oppotsch, J. and Athanassiadis, A. and Fritsch, M. and Heinsius, F.-H. and Held, T. and Hilse, N. and Scherer, V. and Steinke, M. and Wiedner, U.
    Particuology 84 117-125 (2024)
    doi: 10.1016/j.partic.2023.03.005
  • 2024 • 13 Misfit and the mechanism of high temperature and low stress creep of Ni-base single crystal superalloys
    Parsa, A.B. and Bürger, D. and Pollock, T.M. and Eggeler, G.
    Acta Materialia 264 (2024)
    The present work proposes a new elementary deformation mechanism which governs high temperature and low stress creep of single crystal superalloys (SXs), where the misfit between the γ- and the γ′-phase plays a central role. In the coherent two phase SX microstructure, there is a tendency to minimize the overall elastic strain energy. This is accomplished by the formation of dislocation networks in the γ-phase close to the γ/γ’-interfaces. The stress fields of the network dislocations and misfit stresses accommodate each other to keep the overall strain energy of the system at a minimum. Previous work has shown that dynamic recovery is associated with knitting-out reactions, where dislocations from the network shear the γ’-phase and annihilate with dislocations of opposite sign on the other side of the γ’-phase region. Due to the presence of the misfit this results in an increase of elastic strain energy which is counteracted by coupled knitting-in reactions where newly arriving γ-channel dislocations re-establish the minimum energy configuration. Here we provide microstructural evidence for knitting-out and knitting-in reactions and show that while these reactions clearly occur, dislocation network spacings stay constant. The misfit between the γ- and the γ′-phase accounts for a constant network spacing. Dislocation networks are not static but represent dynamic steady state equilibrium structures in an evolving microstructure. Knitting regular networks requires climb processes which are suggested to be rate controlling. This new view of high temperature and low stress creep mechanism of SXs allows to rationalize previous results published in the literature. © 2023
    view abstractdoi: 10.1016/j.actamat.2023.119576
  • 2024 • 12 Tunnel lining segments with enhanced bearing capacity using hybrid concrete concepts
    Petraroia, Diego N. and Plückelmann, Sven and Mark, Peter and Breitenbücher, Rolf
    Tunnelling and Underground Space Technology 143 (2024)
    In general, the design of tunnel lining segments used in mechanized tunneling is dominated by the joints. In fact, the effects of partial area loading dominate segmental failure and, consequently, the concrete bearing capacity of the central region remains underutilized. This paper presents two types of new hybrid segments with enhanced utilization ratios throughout their bodies. The first type comes with strengthened longitudinal joints using high performance steel fiber reinforced concrete, in addition to conventional reinforcement. The second incorporates one-sided barrel-shaped recesses in the central region, which yield volume savings of up to 23.8%. The performance of the new designs is experimentally evaluated on a full-size testing rig made from two steel frames with a capacity of 5 MN each. It captures the on-site conditions in tunnels during service (final state). The first type of segments shows a 74.3% higher loading capacity than a conventional specimen for reference. The second performs even better and possesses 97% higher capacity. In both cases, the failure occurs in the central region. This increases structural safety and simplifies the design. Especially the design of the central region subjected to bending and axial forces gains more relevance against the controversially discussed design of the longitudinal joints. © 2023 Elsevier Ltd
    view abstractdoi: 10.1016/j.tust.2023.105484
  • 2024 • 11 The catalytic effect of iron oxide phases on the conversion of cellulose-derived chars in diluted O2 and CO2
    Pflieger, Christin and Eckhard, Till and Böttger, Jannik and Schulwitz, Jonas and Herrendorf, Tim and Schmidt, Stefan and Salamon, Soma and Landers, Joachim and Wende, Heiko and Kleist, Wolfgang and Muhler, Martin and Cerciello, Francesca
    Applied Energy 353 (2024)
    The conversion of biomass-derived char is substantially influenced by its metal content. One of the main catalytically active metallic elements in biomass is Fe, which occurs in various mineral forms. For the implementation of catalytic effects into char conversion models, investigations on the role of mineral type and loading are required. In this work, the catalytic effect of an Fe sulfate loading series on the oxidation and gasification of an inherently mineral-free cellulose-derived char was analysed. Characterisation focused on the Fe phases present in the char identifying the transformation from FeSO4 to γ-Fe2O3 during doping, and further to ε-Fe2O3 and α-Fe2O3 upon char oxidation as well as to FeO and γ-Fe upon char gasification. Very high loading-dependent activities of ε-Fe2O3 and FeO were quantified by kinetic modelling. These iron oxides strongly catalyse char conversion, lowering the activation energy by up to 14% and 18%, respectively, relative to the mineral-free char. © 2023 Elsevier Ltd
    view abstractdoi: 10.1016/j.apenergy.2023.122068
  • 2024 • 10 Sputter-Deposited La–Co–Mn–O Nanocolumns as Stable Electrocatalyst for the Oxygen Evolution Reaction
    Piotrowiak, Tobias H. and Krysiak, Olga A. and Suhr, Ellen and Zhang, Jian and Zehl, Rico and Kostka, Aleksander and Schuhmann, Wolfgang and Ludwig, Alfred
    Small Structures (2024)
    A thin-film materials library (ML) of the La–Co–Mn–O system is fabricated by hot reactive combinatorial cosputter deposition and screened for its electrocatalytic activity for the oxygen evolution reaction. Within this ML, an area with superior catalytic activity is identified. In-depth characterization of this region reveals a unique columnar-grown microstructure showing a large catalytic surface and excellent stability during electrocatalytic measurements. A zoom-in into these structures shows that the columns are compositionally and structurally not homogeneous but are composed of a mixture of the perovskite phase LaCoMnO3 and Co–Mn–O oxide. Nanoelectrochemistry using the particle on a nanoelectrode approach confirms the high activity as well as stability of the single columns. © 2024 The Authors. Small Structures published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/sstr.202300415
  • 2024 • 9 Convective drying of wood chips: Accelerating coupled DEM-CFD simulations with parametrized reduced single particle models
    Reineking, L. and Fischer, J. and Mjalled, A. and Illana, E. and Wirtz, S. and Scherer, V. and Mönnigmann, M.
    Particuology 84 158-167 (2024)
    doi: 10.1016/j.partic.2023.03.012
  • 2024 • 8 Non-collinear magnetic atomic cluster expansion for iron
    Rinaldi, Matteo and Mrovec, Matous and Bochkarev, Anton and Lysogorskiy, Yury and Drautz, Ralf
    npj Computational Materials 10 (2024)
    The Atomic Cluster Expansion (ACE) provides a formally complete basis for the local atomic environment. ACE is not limited to representing energies as a function of atomic positions and chemical species, but can be generalized to vectorial or tensorial properties and to incorporate further degrees of freedom (DOF). This is crucial for magnetic materials with potential energy surfaces that depend on atomic positions and atomic magnetic moments simultaneously. In this work, we employ the ACE formalism to develop a non-collinear magnetic ACE parametrization for the prototypical magnetic element Fe. The model is trained on a broad range of collinear and non-collinear magnetic structures calculated using spin density functional theory. We demonstrate that the non-collinear magnetic ACE is able to reproduce not only ground state properties of various magnetic phases of Fe but also the magnetic and lattice excitations that are essential for a correct description of finite temperature behavior and properties of crystal defects. © 2024, The Author(s).
    view abstractdoi: 10.1038/s41524-024-01196-8
  • 2024 • 7 Effect of stacking fault energy on the thickness and density of annealing twins in recrystallized FCC medium and high-entropy alloys
    Schneider, Mike and Couzinié, Jean-Philippe and Shalabi, Amin and Ibrahimkhel, Farhad and Ferrari, Alberto and Körmann, Fritz and Laplanche, Guillaume
    Scripta Materialia 240 (2024)
    This work aims to predict the microstructure of recrystallized medium and high-entropy alloys (MEAs and HEAs) with a face-centered cubic structure, in particular the density of annealing twins and their thickness. Eight MEAs and five HEAs from the Cr-Mn-Fe-Co-Ni system are considered, which have been cast, homogenized, cold-worked and recrystallized to obtain different grain sizes. This work thus provides a database that could be used for data mining to take twin boundary engineering for alloy development to the next level. Since the stacking fault energy is known to strongly affect recrystallized microstructures, the latter was determined at 293 K using the weak beam dark-field technique and compared with ab initio simulations, which additionally allowed to calculate its temperature dependence. Finally, we show that all these data can be rationalized based on theories and empirical relationships that were proposed for pure metals and binary Cu-based alloys. © 2023
    view abstractdoi: 10.1016/j.scriptamat.2023.115844
  • 2024 • 6 Mode Transition Induced by Gas Heating Along the Discharge Channel in Capacitively Coupled Atmospheric Pressure Micro Plasma Jets
    Schulenberg, David A. and Vass, Máté and Klich, Maximilian and Donkó, Zoltán and Klotz, Jeldrik and Bibinov, Nikita and Mussenbrock, Thomas and Schulze, Julian
    Plasma Chemistry and Plasma Processing (2024)
    The effects of neutral gas heating along the direction of the gas flow inside the discharge channel of a parallel plate micro atmospheric pressure plasma jet, the COST-jet, on the spatio-temporal dynamics of energetic electrons are investigated by experiments and simulations. The plasma source is driven by a single frequency sinusoidal voltage waveform at 13.56 MHz in helium with an admixture (0.05–0.2%) of nitrogen. Optical emission spectroscopy measurements are applied to determine the spatio-temporally resolved electron impact excitation dynamics from the ground state into the He I (3s) 3 S 1 state and the rotational temperature of nitrogen molecules at different positions along the direction of the gas flow inside the 30 mm long discharge channel. The gas temperature, which is assumed to be equal to the N 2 rotational temperature, is found to increase along the discharge channel. This effect is attenuated as the nitrogen concentration is increased in the gas mixture, leading to an eventually constant temperature profile. The experimental data also reveal a plasma operating mode transition along the discharge channel from the Ω - to the Penning-mode and show good agreement with the results of 1d3v kinetic simulations, which spatially resolve the inter-electrode space and use the gas temperature as an input value. The simulations demonstrate that the increase of the gas temperature leads to the observed mode transition. The results suggest the possibility of using the nitrogen admixture and the feed gas temperature as additional control parameters, (i) to tailor the plasma operating mode along the direction of the gas flow so that the production of specific radicals is optimized; and (ii) to control the final gas temperature of the effluent. The latter could be particularly interesting for biological applications, where the upper gas temperature limit is dictated by the rather low thermal damage threshold of the treated material. © 2024, The Author(s).
    view abstractdoi: 10.1007/s11090-023-10444-6
  • 2024 • 5 Extending the variational quantum eigensolver to finite temperatures
    Selisko, Johannes and Amsler, Maximilian and Hammerschmidt, Thomas and Drautz, Ralf and Eckl, Thomas
    Quantum Science and Technology 9 (2024)
    We present a variational quantum thermalizer (VQT), called quantum-VQT (qVQT), which extends the variational quantum eigensolver to finite temperatures. The qVQT makes use of an intermediate measurement between two variational circuits to encode a density matrix on a quantum device. A classical optimization provides the thermal state and, simultaneously, all associated excited states of a quantum mechanical system. We demonstrate the capabilities of the qVQT for two different spin systems. First, we analyze the performance of qVQT as a function of the circuit depth and the temperature for a one-dimensional Heisenberg chain. Second, we use the excited states to map the complete, temperature dependent phase diagram of a two-dimensional J1-J2 Heisenberg model. Numerical experiments on both quantum simulators and real quantum hardware demonstrate the efficiency of our approach, which can be readily applied to study various quantum many-body systems at finite temperatures on currently available noisy intermediate-scale quantum devices. © 2023 IOP Publishing Ltd
    view abstractdoi: 10.1088/2058-9565/ad1340
  • 2024 • 4 Parametrization protocol and refinement strategies for accurate and transferable analytic bond-order potentials: Application to Re
    Subramanyam, Aparna P. A. and Jenke, Jan and Ladines, Alvin N. and Drautz, Ralf and Hammerschmidt, Thomas
    Physical Review Materials 8 (2024)
    Interatomic potentials provide a means to simulate extended length and time scales that are outside the reach of ab initio calculations. The development of an interatomic potential for a particular material requires the optimization of the parameters of the functional form of the potential. We present a parametrization protocol for analytic bond-order potentials (BOPs) that provides a physically transparent and computationally efficient description of the interatomic interaction. The parametrization protocol of the BOP follows the derivation of the BOP along the coarse-graining of the electronic structure from density-functional theory (DFT) to the tight-binding (TB) bond model to analytic BOPs. In particular, it starts from TB parameters that are obtained by downfolding DFT eigenstates of two-atomic molecules to an sd-valent minimal basis. This sd-valent Hamiltonian is combined with a pairwise repulsion to obtain an initial binding energy relation. The s electrons are then removed from the Hamiltonian and instead represented by an isotropic embedding term. In the final step, the parameters of the remaining d-d interaction, the pair repulsion, and the embedding term are optimized simultaneously. We demonstrate that the application of this parametrization protocol leads to a basic BOP for Re with good transferability. We discuss different strategies to refine the basic BOP towards global transferability or towards local accuracy. We demonstrate that homogeneous samplings of the structural phase space in a map of local atomic environments can be used to systematically increase the global transferability. We also demonstrate the influence of training data weighting on local accuracy refinements with a Pareto-front analysis, and we suggest further requirements to select a final BOP. The local accuracy and global transferability of the final BOP is also shown and compared to DFT. © 2024 American Physical Society.
    view abstractdoi: 10.1103/PhysRevMaterials.8.013803
  • 2024 • 3 Effect of Deformation on the Magnetic Properties of C + N Austenitic Steel
    Torres-Mejía, Laura Gabriela and Paredes-Gil, Katherine and Parra Vargas, Carlos Arturo and Lentz, Jonathan and Weber, Sebastian and Mujica-Roncery, Lais
    Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 55 150 – 160 (2024)
    In this investigation, the effect of deformation on magnetic properties at low temperatures of FeCr18.2Mn18.9–0.96C + N high interstitial steel was studied. Tensile tests were carried out at room temperature and interrupted at 10, 20, and 30 pct deformation. Magnetic measurements were performed through the vibrating sample magnetometry (VSM) technique from 50 K to 370 K. Microstructural, morphological, and crystalline structural analyses by means of XRD and SEM showed that the material consisted of a homogenous and stable austenitic structure with no presence of α-martensite or ε-martensite. Twinning and dislocation cells are suggested as main deformation mechanisms. The material exhibits a paramagnetic–antiferromagnetic (T Néel) transition below 235 K. The Néel temperature of the material tends to increase due to the deformation. A decrease of the magnetization and magnetic susceptibility for the deformed material was measured. Ab initio calculations were performed and showed that the FCC phase is more stable when carbon and nitrogen are added as interstitial elements compared with the free C + N system, additionally, the critical transition temperature was calculated, with a value in agreement with the experimental data. An influence of the magnetic contribution on the SFE was established, being in the order of 5 mJ/m2. © 2023, The Author(s).
    view abstractdoi: 10.1007/s11661-023-07237-z
  • 2024 • 2 Influence of the catalyst precursor for cobalt on activated carbon applied in ammonia decomposition
    Winter, Franziska Luise and Diehl, Patrick and Telaar, Pascal and Watermann, Clara Maria and Kaluza, Stefan and Muhler, Martin and Apfel, Ulf-Peter and Zeidler-Fandrich, Barbara
    Catalysis Today (2024)
    Ammonia is a key compound for storing and transporting green hydrogen. However, the efficient release of stored hydrogen through thermocatalytic ammonia decomposition is achievable only at temperatures around 600 °C, particularly with non-noble metal-based catalysts, which prove to be both ecologically and economically more feasible. In this study, electrically conductive activated carbon was selected as the catalyst support, chosen specifically for its suitability in achieving more energy-efficient direct reactor heating through the ohmic resistance of the catalysts. Cobalt salts were wet impregnated on activated carbon investigating the influence of different precursors (cobalt nitrate and cobalt acetate) and pyrolysis temperatures (400 °C and 600 °C) under N2 flow on the cobalt particle size and the incorporation of cobalt into the carbon matrix. TEM imaging and CO-chemisorption revealed well dispersed cobalt particles with sizes below 10 nm for the catalysts synthesized from the cobalt nitrate precursor. On the other hand, cobalt acetate led to about nine times larger Co agglomerates, which were partially detached from the carbon matrix. Moreover, this substantial difference in the Co particle size results in a significantly higher ammonia conversion for cobalt nitrate-based catalysts, achieving 94 % of ammonia conversion at 600 °C. Furthermore, the long-term stability test of the cobalt nitrate-based catalyst resulted in a slight deactivation of only 2 % ammonia conversion at 500 °C. © 2024 The Authors
    view abstractdoi: 10.1016/j.cattod.2023.114502
  • 2024 • 1 Combinatorial Screening of Electronic and Geometric Effects in Compositionally Complex Solid Solutions Toward a Rational Design of Electrocatalysts
    Zerdoumi, Ridha and Savan, Alan and Amalraj, Marshal and Tetteh, Emmanuel Batsa and Lourens, Florian and Krysiak, Olga A. and Junqueira, João R. C. and Ludwig, Al and Schuhmann, Wolfgang
    Advanced Energy Materials 14 (2024)
    Alloying dissimilar elements presents an effective strategy for enhancing the electrocatalytic properties of multi-metal materials. This enhancement can be attributed to the modification of electronic and geometric effects, which play a crucial role in determining the overall electrocatalytic performance. However, these effects are intricately intertwined and often interrelated due to their coexistence. As a result, the improved catalytic performance of multi-metal systems is frequently attributed to synergistic or “cocktail” effects, without clear explanations of the role of alloying and the individual contribution of each element. A high-throughput experimentation approach is employed to investigate 342 compositions within the quaternary thin film system Pd─Ag─Cu─Fe. The substitution of Cu with Fe (different number of valence electrons) or Ag (different atomic sizes) allows for selective manipulation of electronic or geometric effects, respectively. The substitution of Ag with Fe allows for the simultaneous variation of both effects. The number of valence electrons per unit cell volume is used as a descriptor for electrocatalytic activity, specifically with respect to the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), which can be optimized through independent or simultaneous alteration of electronic and geometric effects. © 2023 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH.
    view abstractdoi: 10.1002/aenm.202302177