Corrosion Behaviors of Long‐Period Stacking Ordered Structure in Mg Alloys Used in Biomaterials: A Review

The long‐period stacking ordered (LPSO) phases have distinctive microstructures and significant effect on the promotion of mechanical properties of Mg alloys, which have received considerable attention not only as industrial materials but also as biodegradable implant materials recently. By now, numerous researchers devote to study the effects of the microstructures of LPSO phases on the mechanical properties of Mg alloys. But a few of them reveal the relationship between LPSO phases and corrosion behaviors of Mg alloys. Therefore, the knowledge of characteristics of LPSO phases and their effects on biocorrosion behaviors is essential. In this review, the current understanding about the structure, growth, transformation, and deformation of LPSO phases in Mg alloys are summarized. The recent developments of biocorrosion behaviors of Mg alloys are reviewed. The information on the immersion and corrosion mechanisms of Mg alloys are provided. The role of LPSO structures on corrosion behaviors of Mg alloys is intensively analyzed. Based on the current understandings, some problems are pointed out and suggestions for further research of Mg alloys with LPSO structures using as biomedical materials are provided.

     

关于镁合金中长周期有序结构的研究综述

系统地介绍了6H、10H、14H、18R、24R型LPSO结构的原子堆垛和RE、Zn的占位特点,探讨了LPSO结构的形成条件和形成机制,分析了含LPSO结构相合金的组织演变过程并概述了组织演变方面最新的研究成果,总结了含LPSO结构相镁合金的室温和高温性能的研究现状,最后对该类合金未来的研究方向进行了展望。     

Al20Si20Mn20Fe20Ga20中近等原子比高熵十次准晶

准晶是结构复杂相,通常以一种合金元素为主要成分.高熵合金含有多种主要合金元素,其晶体结构却往往是比较简单的立方相.作为结构和成分均复杂的高熵准晶却难以在实验上制备和理论上预测,研究人员对其结构特点也知之甚少.因而高熵准晶的制备和结构特性引起了人们的广泛关注.我们报道了一种在Al20Si20Mn20Fe20Ga20甩带样...     

Atomic Structure and Electrical Activity of Grain Boundaries and Ruddlesden–Popper Faults in Cesium Lead Bromide Perovskite

To evaluate the role of planar defects in lead‐halide perovskites—cheap, versatile semiconducting materials—it is critical to examine their structure, including defects, at the atomic scale and develop a detailed understanding of their impact on electronic properties. In this study, postsynthesis nanocrystal fusion, aberration‐corrected scanning transmission electron microscopy, and first‐principles calculations are combined to study the nature of different planar defects formed in CsPbBr₃ nanocrystals. Two types of prevalent planar defects from atomic resolution imaging are observed: previously unreported Br‐rich [001](210)∑5 grain boundaries (GBs) and Ruddlesden–Popper (RP) planar faults. The first‐principles calculations reveal that neither of these planar faults induce deep defect levels, but their Br‐deficient counterparts do. It is found that the ∑5 GB repels electrons and attracts holes, similar to an n–p–n junction, and the RP planar defects repel both electrons and holes, similar to a semiconductor–insulator–semiconductor junction. Finally, the potential applications of these findings and their implications to understand the planar defects in organic–inorganic lead‐halide perovskites that have led to solar cells with extremely high photoconversion efficiencies are discussed.     

Atomic‐Scale Structure Evolution in a Quasi‐Equilibrated Electrochemical Process of Electrode Materials for Rechargeable Batteries

Lithium‐ion batteries have proven to be extremely attractive candidates for applications in portable electronics, electric vehicles, and smart grid in terms of energy density, power density, and service life. Further performance optimization to satisfy ever‐increasing demands on energy storage of such applications is highly desired. In most of cases, the kinetics and stability of electrode materials are strongly correlated to the transport and storage behaviors of lithium ions in the lattice of the host. Therefore, information about structural evolution of electrode materials at an atomic scale is always helpful to explain the electrochemical performances of batteries at a macroscale. The annular‐bright‐field (ABF) imaging in aberration‐corrected scanning transmission electron microscopy (STEM) allows simultaneous imaging of light and heavy elements, providing an unprecedented opportunity to probe the nearly equilibrated local structure of electrode materials after electrochemical cycling at atomic resolution. Recent progress toward unraveling the atomic‐scale structure of selected electrode materials with different charge and/or discharge state to extend the current understanding of electrochemical reaction mechanism with the ABF and high angle annular dark field STEM imaging is presented here. Future research on the relationship between atomic‐level structure evolution and microscopic reaction mechanisms of electrode materials for rechargeable batteries is envisaged.     

Crystal structure of the orthorhombic U2-Al4Mg4Si4 precipitate in the Al–Mg–Si alloy system and its relation to the β′ and β″ phases

The atomic structure of a common precipitate in the Al–Mg–Si system has been determined. It is isotypic with TiNiSi (space group Pnma) and contains four units of MgAlSi in a unit cell of size a = 0.675 nm, b = 0.405 nm, c = 0.794 nm. EDS analyses support the composition. A model was based on the atomic structure of the β′ precipitate, electron diffraction and high-resolution transmission electron microscopy (HRTEM) images. A quantum mechanical refinement of the model removed discrepancies between simulated and experimental diffraction intensities. Finally, a multi-slice least square refinement confirmed the structure. The structural relation with β″ is investigated. A similar Mg–Si plane also existing in β″ and β′, can explain most coherency relations between the precipitate phases and with matrix.     

Direct Observations of the Formation and Redox‐Mediator‐Assisted Decomposition of Li2O2 in a Liquid‐Cell Li–O2 Microbattery by Scanning Transmission Electron Microscopy

Operando scanning transmission electron microscopy observations of cathodic reactions in a liquid‐cell Li–O₂ microbattery in the presence of the redox mediator tetrathiafulvalene (TTF) in 1.0 m LiClO₄ dissolved dimethyl sulfoxide electrolyte are reported. It is found that the TTF addition does not obviously affect the discharge reaction for the formation of a solid Li₂O₂ phase. The coarsening of Li₂O₂ nanoparticles occurs via both conventional Ostwald ripening and nonclassical crystallization by particle attachment. During charging, the oxidation reaction at significantly reduced charge potentials mainly takes place at Li₂O₂/electrolyte interfaces and has obvious correspondence with the oxidized TTF⁺ distributions in the electric fields of the charged electrode. This study provides direct evidence that TTF truly plays a role in promoting the decomposition of Li₂O₂ as a soluble charge‐transfer agent between the electrode and the Li₂O₂.     

Uptake and Intracellular Fate of Engineered Nanoparticles in Mammalian Cells: Capabilities and Limitations of Transmission Electron Microscopy—Polymer‐Based Nanoparticles

In order to elucidate mechanisms of nanoparticle (NP)–cell interactions, a detailed knowledge about membrane–particle interactions, intracellular distributions, and nucleus penetration capabilities, etc. becomes indispensable. The utilization of NPs as additives in many consumer products, as well as the increasing interest of tailor‐made nanoobjects as novel therapeutic and diagnostic platforms, makes it essential to gain deeper insights about their biological effects. Transmission electron microscopy (TEM) represents an outstanding method to study the uptake and intracellular fate of NPs, since this technique provides a resolution far better than the particle size. Additionally, its capability to highlight ultrastructural details of the cellular interior as well as membrane features is unmatched by other approaches. Here, a summary is provided on studies utilizing TEM to investigate the uptake and mode‐of‐action of tailor‐made polymer nanoparticles in mammalian cells. For this purpose, the capabilities as well as limitations of TEM investigations are discussed to provide a detailed overview on uptake studies of common nanoparticle systems supported by TEM investigations. Furthermore, methodologies that can, in particular, address low‐contrast materials in electron microscopy, i.e., polymeric and polymer‐modified nanoparticles, are highlighted.     

Microstructures and mechanical properties of as‐cast titanium–zirconium–molybdenum ternary alloys

In this study titanium–zirconium–molybdenum alloys (Ti₅₀Zr₅₀)_100‐xMo_x (xMo; x = 0 at.%, 1 at.%, 3 at.%, 5 at.% or 7 at.%) were investigated, focusing on the effect of molybdenum addition on their microstructures and mechanical properties. Transmission electron microscopy observations revealed that the binary Ti₅₀Zr₅₀ alloy was composed entirely of an acicular hexagonal structure of the α’ phase. When the molybdenum content was 1 at.%, the alloy was composed of β and ω phases. However, when 3 at.% or more molybdenum was added, only the equiaxed, retained β phase was observed. Tensile tests at room temperature indicated that the mechanical properties of the 1Mo alloy were inferior owing to the embrittlement effects of the ω phase and the difficulty of dislocation motion through the ω phase. Our research suggested that the 5Mo alloy had excellent ductility (16.5 %) as well as adequate strength (780 MPa). The improved mechanical properties were attributed to the enhanced stability of the β phase and the disappearance of the ω phase.     

Recent breakthroughs and perspectives of high-energy layered oxide cathode materials for lithium ion batteries

Ni-rich layered oxides (NRLOs) and Li-rich layered oxides (LRLOs) have been considered as promising next-generation cathode materials for lithium ion batteries (LIBs) due to their high energy density, low cost, and environmental friendliness. However, these two layered oxides suffer from similar problems like capacity fading and different obstacles such as thermal runaway for NRLOs and voltage decay for LRLOs. Understanding the similarities and differences of their challenges and strategies at multiple scales plays a paramount role in the cathode development of advanced LIBs. Herein, we provide a comprehensive review of state-of-the-art progress made in NRLOs and LRLOs based on multi-scale insights into electrons/ions, crystals, particles, electrodes and cells. For NRLOs, issues like structure disorder, cracks, interfacial degradation and thermal runaway are elaborately discussed. Superexchange interaction and magnetic frustration are blamed for structure disorder while strains induced by universal structural collapse result in issues like cracks. For LRLOs, we present an overview of the origin of high capacity followed by local crystal structure, and the root of voltage hysteresis/decay, which are ascribed to reduced valence of transition metal ions, phase transformation, strains, and microstructure degradation. We then discuss failure mechanism in full cells with NRLO cathode and commercial challenges of LRLOs. Moreover, strategies to improve the performance of NRLOs and LRLOs from different scales such as ion-doping, microstructure designs, particle modifications, and electrode/electrolyte interface engineering are summarized. Dopants like Na, Mg and Zr, delicate gradient concentration design, coatings like spinel LiNi_0.5Mn_1.5O₄ or Li₃PO₄ and novel electrolyte formulas are highly desired. Developing single crystals for NRLOs and new crystallographic structure or heterostructure for LRLOs are also emphasized. Finally, remaining challenges and perspectives are outlined for the development of NRLOs and LRLOs. This review offers fundamental understanding and future perspectives towards high-performance cathodes for next-generation LIBs.