Impact of defects on magnetic properties of spinel zinc ferrite thin films. - In: Physica status solidi, ISSN 1521-3951, Bd. 257 (2020), 7, 1900630, insges. 11 S.
The recent developments in the study of magnetic properties in the spinel zinc ferrite system are explored. Engineering of ionic valence and site distribution allows tailoring of magnetic interactions. Recent literature is reviewed, and own investigations are presented for a conclusive understanding of the mechanisms responsible for the magnetic behavior in this material system. By varying the Zn-to-Fe ratio, the deposition, as well as thermal annealing conditions, ZnFe2O4 thin films with a wide range of crystalline quality are produced. In particular, the focus is on the magnetic structure in relation to spectroscopic properties of disordered ZnFe2O4 thin films. Comparing the cation distribution in film bulk (optical transitions in the dielectric function) and near-surface region (X-ray absorption), it is found that an inhomogeneous cation distribution leads to a weaker magnetic response in films of inverse configuration, whereas defects in the normal spinel are likely to be found at the film surface. The results show that it is possible to engineer the defect distribution in the magnetic spinel ferrite film structure and tailor their magnetic properties on demand. It is demonstrated that these properties can be read out optically, which allows controlled growth of the material and applications in future magneto-optical devices.
https://doi.org/10.1002/pssb.201900630
Experimental characterization and numerical analysis of additively manufactured mild steel under monotonic loading conditions. - In: Progress in additive manufacturing, ISSN 2363-9520, Bd. 5 (2020), 3, S. 295-304
Additive Manufacturing (AM), for the case of metals, is a technology developed to create 3D products by following a layer-by-layer welding procedure. In this work, the tensile behavior of wire arc additively manufactured mild steel is studied experimentally and numerically. The microstructure of the metal is strongly influenced by the AM process that involves several heating and cooling cycles; therefore, it is first analyzed with optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction to identify the different phases and to extract the grain properties. With this information, two approaches are used to build the Representative Volume Element, which will be part of a multi-scale material model. The first approach constitutes a synthetic generation of grains according to a Voronoi Tessellation and the second one an image-based representation. Afterwards, a virtual tensile test for the determination of the stress-strain relation of the material is performed, which is later compared with the measurements of a real tensile test carried out on several specimens that were obtained using the wire arc additive manufacturing technique.
https://doi.org/10.1007/s40964-020-00111-z
Multiferroic bismuth ferrite: perturbed angular correlation studies on its ferroic α-β phase transition. - In: Physical review, ISSN 2469-9969, Bd. 102 (2020), 22, S. 224110-1-224110-11
https://doi.org/10.1103/PhysRevB.102.224110
Herstellung von 3D-gedruckten Stahlknoten : vom Entwurf bis zur Herstellung von Strukturen. - In: Stahlbau, ISSN 1437-1049, Bd. 89 (2020), 12, S. 956-969
Es wird ein Einblick in die Vorgehensweise zur Fertigung von Knotenstrukturen im Stahlbau mittels Wire and Arc Additive Manufacturing (WAAM) und der numerischen und experimentellen Untersuchung der Knotenstrukturen gegeben. Ausgehend von der geometrischen Komplexität sich schneidender Profilstäbe aus Stahl werden wesentliche Punkte bei der simulationsgestützten Ermittlung von Knotenstrukturen beschrieben. In Abhängigkeit von den Lastfällen können unterschiedliche Strukturen in der Topologieoptimierung gefunden werden. Für die Herstellung der Knotenstruktur durch das Wire and Arc Additive Manufacturing müssen die numerisch gefundene Geometrie angepasst sowie Varianten der Bahnplanung entwickelt und bewertet werden. Dabei wird auch der Einfluss von Prozessparametern auf Verzug, Endkonturnähe und mechanische Eigenschaften der Bauteile untersucht. Für die Prognose von Spannungs- und Verformungszuständen des Knotens wird eine vereinfachte thermische und mechanische Analyse des Herstellungsprozesses durchgeführt. Weiter wird ein Verfahren für eine In-situ-Bauteilprüfung vorgestellt, welche Prozessunregelmäßigkeiten anhand von Sensordaten erkennt und deren Einflüsse auf die mechanischen Eigenschaften des Bauteils bewertet, wodurch frühzeitig im Prozess Maßnahmen zur Fehlerkorrektur getroffen oder Kosten durch Ausschuss reduziert werden können.
https://doi.org/10.1002/stab.202000080
Atomic surface structure of MOVPE-prepared GaP(111)B. - In: Applied surface science, Bd. 534 (2020), 147346
Controlling the surface formation of the group-V face of (111)-oriented III-V semiconductors is crucial for subsequent successful growth of III-V nanowires for electronic and optoelectronic applications. With a view to preparing GaP/Si(111) virtual substrates, we investigate the atomic structure of the MOVPE (metalorganic vapor phase epitaxy)-prepared GaP(111)B surface (phosphorus face). We find that upon high-temperature annealing in the H2-based MOVPE process ambience, the surface is phosphorus-depleted, as evidenced by X-ray photoemission spectroscopy (XPS). However, a combination of density functional theory calculations and scanning tunneling microscopy (STM) suggests the formation of a partially H-terminated phosphorus surface, where the STM contrast is due to electrons tunneling from non-terminated dangling bonds of the phosphorus face. Atomic force microscopy (AFM) reveals that a high proportion of the surface is covered by islands, which are confirmed as Ga-rich by Auger electron spectroscopy (AES). We conclude that the STM images of the samples after high-temperature annealing only reflect the flat regions of the partially H-terminated phosphorus face, whereas an increasing coverage with Ga-rich islands, as detected by AFM and AES, forms upon annealing and underlies the higher proportion of Ga in the XPS measurements.
https://doi.org/10.1016/j.apsusc.2020.147346
Suppression of complex hysteretic resonances in varying compliance vibration of a ball bearing. - In: Shock and vibration, ISSN 1875-9203, (2020), 8825902, insges. 11 S.
It is traditionally considered that, due to the Hertzian contact force-deformation relationship, the stiffness of rolling bearings has stiffening characteristics, and gradually researchers find that the supporting characteristics of the system may stiffen, soften, and even coexist from them. The resonant hysteresis affects the stability and safety of the system, and its jumping effect can make an impact on the system. However, the ball bearing contains many nonlinearities such as the Hertzian contact between the rolling elements and raceways, bearing clearance, and time-varying compliances (VC), leading great difficulties to clarify the dynamical mechanism of resonant hysteresis of the system. With the aid of the harmonic balance and alternating frequency/time domain (HB-AFT) method and Floquet theory, this paper will investigate the hysteretic characteristics of the Hertzian contact resonances of a ball bearing system under VC excitations. Moreover, the linearized dynamic bearing stiffness of the system will be presented for assessing the locations of VC resonances, and the nonlinear characteristics of bearing stiffness will also be discussed in depth. Our analysis indicates that the system possesses many types of VC resonances such as the primary, internal, superharmonic, and even combination resonances, and the evolutions of these resonances are presented. Finally, the suppression of resonances and hysteresis of the system will be proposed by adjusting the bearing clearance.
https://doi.org/10.1155/2020/8825902
Control of magnetic properties in spinel ZnFe2O4 thin films through intrinsic defect manipulation. - In: Journal of applied physics, ISSN 1089-7550, Bd. 128 (2020), 16, 165702, insges. 7 S.
Im Titel sind "2" und "4" tiefgestellt
We present a systematic study of the magnetic properties of ZnFe2O4 thin films fabricated by pulsed laser deposition at low and high oxygen partial pressure and annealed in oxygen and argon atmosphere, respectively. The as-grown films show strong magnetization, closely related to a non-equilibrium distribution of defects, namely, Fe cations among tetrahedral and octahedral lattice sites. While the concentration of tetrahedral Fe cations declines after argon treatment at 250 ˚C, the magnetic response is enhanced by the formation of oxygen vacancies, evident by the increase in near-infrared absorption due to the Fe2+-Fe3+ exchange. After annealing at temperatures above 300 ˚C, the weakened magnetic response is related to a decline in disorder with a partial recrystallization toward a less defective spinel configuration.
https://doi.org/10.1063/5.0019712
Production of topology-optimized structural nodes by means of arc-based, additive manufacturing with MSG welding process :
Topologieoptimierte Tragwerksknoten : Herstellung mittels lichtbogenbasierter, additiver Fertigung mit MSG-Schweißprozess. - In: Industrie 4.0 Management, ISSN 2364-9208, Bd. 36 (2020), 4, S. 15-19
In diesem Beitrag wird die Erzeugung von festigkeits- und steifigkeitsangepassten Tragstrukturen mittels der numerischen Simulationsmethode der Topologieoptimierung vogestellt. Der dabei resultierende Tragwerksknoten wird mittels CAD/CAM-Software in eine Robotorbahnplanung überführt und mit der drahtbasierten, additiven Fertigung unter Verwendung des MSG-Schweißprozesses aus dem Schweißzusatzwerkstoffs G4Si1 hergestellt.
Formation of near-surface melt films on glass ceramics due to ultrashort laser pulses. - In: Applied physics, ISSN 1432-0630, Volume 126 (2020), issue 11, article number 878, Seite 1-12
Glass ceramics are highly specialized composite materials, which have a partly polycrystalline and a partly glassy state. Due to their special properties such as good mechanical strength, low thermal expansion, and excellent thermal shock resistance, they are especially well known for their use in consumer goods industry. But also in the high-tech sector, like optics or microsystems technology, the applications for glass ceramics are constantly growing. Simultaneously, the continuing miniaturization of microelectronic components requires precise, high-resolution processing methods. While mechanical processing is limited due to the brittle-hard properties of the material, ultrashort pulse lasers can serve as an ideal tool for this purpose. The pulse durations in the pico- and femtosecond range are known to enable a highly precise and gentle processing with very small thermal load for the workpiece. Therefore, the process is often referred to as cold ablation. It has been known for some time, however, that if pulse energies and repetition rates are sufficiently high, heat accumulation effects can occur. In this article, we report on surface modifications on glass ceramics arising during femtosecond ablation. Using Low Temperature Co-fired Ceramics (LTCC) as an example, we show that even at low repetition rates of 100 kHz and moderate average laser power below 3 W several micrometer thick molten patterns can emerge. Another peculiarity of the observed phenomenon lies in the increase of the vitreous layer with decreasing pulse duration. The dependence of the effect on the material structure is investigated by means of X-ray diffraction (XRD) measurements.
https://doi.org/10.1007/s00339-020-04001-7
Sensor micro and nanoparticles for microfluidic application. - In: Applied Sciences, ISSN 2076-3417, Bd. 10 (2020), 23, 8353, S. 1-37
Micro and nanoparticles are not only understood as components of materials but as small functional units too. Particles can be designed for the primary transduction of physical and chemical signals and, therefore, become a valuable component in sensing systems. Due to their small size, they are particularly interesting for sensing in microfluidic systems, in microarray arrangements and in miniaturized biotechnological systems and microreactors, in general. Here, an overview of the recent development in the preparation of micro and nanoparticles for sensing purposes in microfluidics and application of particles in various microfluidic devices is presented. The concept of sensor particles is particularly useful for combining a direct contact between cells, biomolecules and media with a contactless optical readout. In addition to the construction and synthesis of micro and nanoparticles with transducer functions, examples of chemical and biological applications are reported.
https://doi.org/10.3390/app10238353