The combination of different phase constituents to realize a mechanical composite effect for superior strength-ductility synergy has become an important strategy in microstructure design in advanced ...high-strength steels. Introducing multiple phases in the microstructure essentially produces a large number of phase boundaries. Such hetero-interfaces affect the materials in various aspects such as dislocation activity and damage formation. However, it remains a question whether the characteristics of phase boundaries, such as their chemical decoration states, would also have an impact on the mechanical behavior in multiphase steels. Here we reveal a phase boundary segregation-induced strengthening effect in ultrafine-grained duplex medium-Mn steels. We found that the carbon segregation at ferrite-austenite phase boundaries can be manipulated by adjusting the cooling conditions after intercritical annealing. Such phase boundary segregation in the investigated steels resulted in a yield strength enhancement by 100–120 MPa and simultaneously promoted discontinuous yielding. The sharp carbon segregation at the phase boundaries impeded interfacial dislocation emission, thus increasing the stress required to activate such dislocation nucleation process and initiate plastic deformation. This observation suggests that the enrichment of carbon at the phase boundaries can enhance the energy barrier for dislocation emission, which provides a favorable condition for plastic flow avalanches and thus discontinuous yielding. These findings extend the current understanding of the yielding behavior in medium-Mn steels, and more importantly, shed light on utilizing and manipulating phase boundary segregation to improve the mechanical performance of multiphase metallic materials.
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O3-type layered NaNi0.5Ti0.5O2, which has been reported previously as a promising cathode material for Na-ion batteries, has been characterized using comprehensive operando techniques combined with ...electrochemical and magnetization measurements. Operando Synchrotron diffraction revealed a reversible O3–P3 transformation during charge and discharge without any intermediate phases, which stands in contrast to NaNiO2 and NaNi0.5Mn0.5O2. Operando X-ray absorption studies showed that the electrochemical process in the potential window of 1.5–4.2 V vs Na+/Na is sustained exclusively by Ni oxidation and reduction while Ti remains inactive. These findings are further supported by ex situ magnetization measurements, yielding a lower paramagnetic moment in the charged state in agreement with Ni oxidation. On the basis of these insights, we elaborate on the beneficial stabilizing effect of Ti. However, a strong C-rate dependence for NaNi0.5Ti0.5O2 and NaNi0.5Mn0.5O2 during cycling known from the literature points at a rather high influence of the original structure stacking and the associated Na migration paths.
Abstract
Porphyrin-based metal–organic frameworks (MOFs), exemplified by MOF-525, PCN-221, and PCN-224, are promising systems for catalysis, optoelectronics, and solar energy conversion. However, ...subtle differences between synthetic protocols for these three MOFs give rise to vast discrepancies in purported product outcomes and description of framework topologies. Here, based on a comprehensive synthetic and structural analysis spanning local and long-range length scales, we show that PCN-221 consists of Zr
6
O
4
(OH)
4
clusters in four distinct orientations within the unit cell, rather than Zr
8
O
6
clusters as originally published, and linker vacancies at levels of around 50%, which may form in a locally correlated manner. We propose disordered PCN-224 (
d
PCN-224) as a unified model to understand PCN-221, MOF-525, and PCN-224 by varying the degree of orientational cluster disorder, linker conformation and vacancies, and cluster–linker binding. Our work thus introduces a new perspective on network topology and disorder in Zr-MOFs and pinpoints the structural variables that direct their functional properties.
Mixed solid solutions have played an important role in improving the kinetics and performance of hydrogen storage materials, as reported for the Li–Mg–N–H, K–Mg–N–H, and Rb–Mg–N–H systems. Besides, ...the formation of a homogeneous solid solution, mostly due to partial ionic substitution, is known to be an effective approach to improve the ionic conductivity of a material, which is an important property in electrochemical applications. We have reported a series of solid solutions based on mixed amide-hydride materials of the Group 1 elements, e.g., K(NH2) x H1–x , Rb(NH2) x H1–x , and Cs(NH2) x H1–x , via the exchange of NH2 –/H– anions with the change of the lattice cell of the solid solution. Extending the research in this direction, we study the M–N–H solid solution in the MNH2–MH systems (M = K, Rb, Cs, and their combinations), i.e., KNH2–RbH, RbNH2–KH, RbNH2–CsH, and CsNH2–RbH via ex situ/in situ XRD, IR, and 1H 2D solid-state NMR. The results obtained confirm the formation of mixed metal amide-hydride solid solutions associated with an exchange between both anionic (NH2 – and H–) and cationic species (K+, Rb+, and Cs+). With this study, we aim to create an accessible library of M–N–H solid solutions for further studies as additives for hydrogen storage materials or ionic conductors.
Abstract
Here, we introduce phase change mechanisms in lead-free piezoceramics as a strategy to utilize attendant volume change for harvesting large electrostrain. In the newly developed (K,Na)NbO
3
...solid-solution at the polymorphic phase boundary we combine atomic mapping of the local polar vector with in situ synchrotron X-ray diffraction and density functional theory to uncover the phase change and interpret its underlying nature. We demonstrate that an electric field-induced phase transition between orthorhombic and tetragonal phases triggers a dramatic volume change and contributes to a huge effective piezoelectric coefficient of 1250 pm V
−1
along specific crystallographic directions. The existence of the phase transition is validated by a significant volume change evidenced by the simultaneous recording of macroscopic longitudinal and transverse strain. The principle of using phase transition to promote electrostrain provides broader design flexibility in the development of high-performance piezoelectric materials and opens the door for the discovery of high-performance future functional oxides.
In this study, Synchrotron X-ray diffraction (XRD) radiography was utilized to investigate the ageing heterogeneity in 48 Ah prismatic lithium-ion cells with Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) as ...the positive electrode active material and graphite as the negative electrode active material after ∼2800 cycles. The study revealed that the area closest to the positive electrode tab is most vulnerable to degradation, particularly impacting the NMC material. Application of principal component analysis allowed to differentiate and visualize part of positive electrode material that has a different degradation due to the lithium plating. A comparison of non-destructive X-ray diffraction-based methods and electrochemical characterization method which was performed on the opened cell has shown an importance of a complementary approach. Our results highlight the feasibility of employing non-destructive techniques to study large prismatic cells, thereby presenting extensive opportunities for advancements in battery research and industry.
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•Use of X-Ray diffraction radiography to study an automotive grade prismatic cell.•Non-destructive resolution of heterogeneous ageing inside a prismatic cell.•Application of Principal Component Analysis to X-Ray diffraction radiography data.•Demonstration of different degradation pathway for lithium plated regions.
The fabrication of three-dimensional assemblies consisting of large quantities of nanowires is of great technological importance for various applications including (electro-)catalysis, sensitive ...sensing, and improvement of electronic devices. Because the spatial distribution of the nanostructured material can strongly influence the properties, architectural design is required in order to use assembled nanowires to their full potential. In addition, special effort has to be dedicated to the development of efficient methods that allow precise control over structural parameters of the nanoscale building blocks as a means of tuning their characteristics. This paper reports the direct synthesis of highly ordered large-area nanowire networks by a method based on hard templates using electrodeposition within nanochannels of ion track-etched polymer membranes. Control over the complexity of the networks and the dimensions of the integrated nanostructures are achieved by a modified template fabrication. The networks possess high surface area and excellent transport properties, turning them into a promising electrocatalyst material as demonstrated by cyclic voltammetry studies on platinum nanowire networks catalyzing methanol oxidation. Our method opens up a new general route for interconnecting nanowires to stable macroscopic network structures of very high integration level that allow easy handling of nanowires while maintaining their connectivity.
Increased formability of aluminium alloys has been demonstrated via cryogenic deformation. In previous studies, the microstructures of samples deformed at low temperatures were analysed after ...reheating to room temperature (RT) and storage. However, after heating the dislocation structure and density of the deformed material do not reflect the cryogenic situation. In this work, we investigate the evolution of flow stress during recovery in Al-Mg and Al-Mg-Si alloys. We examine the RT recovery behaviour of samples pre-strained at 77 K to different strain levels, and evaluate the structural stability upon subsequent deformation. We also study microstructural evolution via in-situ synchrotron X-ray diffraction, starting from initial conditions at cryogenic temperatures to long-term RT-recovery. Recovery of cryogenically deformed samples at RT results in reduction of the flow stress, in dependence on RT storage. The recovery process can be divided into three distinct sections, each based on a different mechanism characterized by either the arranging or the annihilation of dislocations. Subsequent further straining at room temperature after cryogenic forming also generates plastic instabilities and premature fracture due to unfavourable hardening and recovery assisted softening interplay.
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•Room temperature recovery after cryogenic deformation can be divided into three different mechanistic phases•These can be distinguished by dislocation rearrangement, dislocation annihilation and a change in strength (stress drop)•Room temperature deformation directly after cryogenic deformation can result in immediate fracture
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