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As a refractory transition-metal diboride, monolithic TiB2 oxidizes at temperatures below 400 °C. Here, we performed detailed microstructural investigations to study the low-temperature oxidation mechanism of monolithic TiB2. An anomalous rapid oxidation behavior is observed at ∼ 500 °C, where the oxidation rate is much higher than that at a higher temperature of 650 °C. The anomalous rapid oxidation behavior originates from an unreported bi-layer oxide scale consisting of outer homogeneous B2O3/TiO2 mixed layer with a supra-nanometre-sized dual-phase amorphous-crystal microstructure and inner unstable Ti-B-O amorphous layer. By contrast, the oxide scale changes from homogeneous mixed microstructure to a laminated configuration at 650 °C, restoring the superior oxidation resistance. Our experimental results indicate that it is the configuration of the oxide scale that determines primarily the oxidation behavior of TiB2, which has been seldom envisaged in previous studies.

Rechargeable lithium-carbon dioxide (Li-CO2) batteries have attracted much attention due to their high theoretical energy densities and capture of CO2. However, the electrochemical reaction mechanisms of rechargeable Li-CO2 batteries, particularly the decomposition mechanisms of the discharge product Li2CO3 are still unclear, impeding their practical applications. Exploring electrochemistry of Li2CO3 is critical for improving the performance of Li-CO2 batteries. Herein, in-situ environmental transmission electron microscopy (ETEM) technique was used to study electrochemistry of Li2CO3 in Li-CO2 batteries during discharge and charge processes. During discharge, Li2CO3 was nucleated and accumulated on the surface of the cathode media such as carbon nanotubes (CNTs) and Ag nanowires (Ag NWs), but it was hard to decompose during charging at room temperature. To promote the decomposition of Li2CO3, the charge reactions were conducted at high temperatures, during which Li2CO3 was decomposed to lithium with release of gases. Density functional theory (DFT) calculations revealed that the synergistic effect of temperature and biasing facilitates the decomposition of Li2CO3. This study not only provides a fundamental understanding to the high temperature Li-CO2 nanobatteries, but also offers a valid technique, i.e., discharging/charging at high temperatures, to improve the cyclability of Li-CO2 batteries for energy storage applications.

Akin to Li, Na deposits in a dendritic form to cause short circuit in Na metal batteries. However, the growth mechanisms and related mechanical properties of Na dendrites remain largely unknown. He...

Lithium metal is considered the ultimate anode material for future rechargeable batteries1,2, but the development of Li metal-based rechargeable batteries has achieved only limited success due to uncontrollable Li dendrite growth3–7. In a broad class of all-solid-state Li batteries, one approach to suppress Li dendrite growth has been the use of mechanically stiff solid electrolytes8,9. However, Li dendrites still grow through them10,11. Resolving this issue requires a fundamental understanding of the growth and associated electro-chemo-mechanical behaviour of Li dendrites. Here, we report in situ growth observation and stress measurement of individual Li whiskers, the primary Li dendrite morphologies12. We combine an atomic force microscope with an environmental transmission electron microscope in a novel experimental set-up. At room temperature, a submicrometre whisker grows under an applied voltage (overpotential) against the atomic force microscope tip, generating a growth stress up to 130 MPa; this value is substantially higher than the stresses previously reported for bulk13 and micrometre-sized Li14. The measured yield strength of Li whiskers under pure mechanical loading reaches as high as 244 MPa. Our results provide quantitative benchmarks for the design of Li dendrite growth suppression strategies in all-solid-state batteries. Lithium whisker growth and mechanical properties can be studied in situ using a combination of two microscopies.

It is a highly relevant topic concerning how to improve the electrochemical performance of anode materials for the next generation lithium-ion batteries (LIBs). Herein, for the first time, we report a facile and controllable approach to modify MoS2 nanosheets, a typical 2D material, as an anode material for advanced LIBs via oxygen plasma engineering. An oxygen plasma treatment not only generates vacancies/defects but also incorporates heteroatom doping to form Mo–O–C bonds. This unique hybrid specialty enables the oxygen-plasma-treated MoS2 to achieve superior electrochemical performance with high reversible capacities, a long-term cycle life, and good rate capabilities. The plasma-assisted modification is believed to be applicable for other 2D materials as an efficient anode for energy storages.

Metal-air batteries have much higher theoretical energy density than metal ion batteries, however, their application is hampered by the sluggish oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). As such, electrocatalysis is employed to facilitate the ORR and OER. Despite enormous efforts, real time imaging of the electrocatalysis during the ORR and OER processes remain elusive. Furthermore, it is controversial whether or not electrocatalysis is necessary in the Na-O2 battery. Here we show the first in-situ imaging of the operation of the electrocatalysis in a Na-O2 battery in an advanced aberration corrected environmental transmission electron microscopy (ETEM). In the Au-coated MnO2 nanowire air cathode, the ORR is characterized by the formation of NaO2 nano bubbles nucleated from the Au catalysts, causing an 18 times volume increase on the surface of the MnO2 nanowires; the NaO2 quickly disproportionated to Na2O2 and O2, causing collapse of the NaO2 nano bubbles. In contrast, no ORR took place in the bare MnO2 nanowire cathode; instead, the MnO2 nanowires only swelled 217% as a result of the Na+ intercalation. The results provide not only new insight into the Au-catalyzed oxygen chemistry in the Na-O2 battery, but also an atom-level characterization technique to evaluate the electrocatalysis in the metal air batteries.

The mechanisms responsible for the deformation of nanocrystalline materials are not well understood although many mechanisms have been proposed. This article studies the room-temperature stress-strain relations of bulk nanocrystalline silver deformed in a tension mode at a constant strain rate. Synchrotron X-ray diffraction patterns were gathered from the deformed specimen and used to deduce such structural parameters as the grain size and the density of dislocations, twins, and stacking faults. Our quantitative results indicate that grain growth and twinning occur in the stage of elastic deformation. Detwinning and accumulation of stacking faults occur in the early stage of plastic deformation, where the strength of nanocrystalline silver correlates well with the square root of stacking faults probability. Grain shrinking and generation of statistically stored dislocations occur in the final stage of plastic deformation, where the strength of nanocrystalline silver correlates well with the square root of the density of dislocations (statistically stored and geometrically necessary). Our results suggest that multiple deformation mechanisms such as grain growth, grain shrinking, twinning, detwinning, stacking faults, and dislocations, rather than a single deformation mechanism, occur in the elastic and plastic deformation stages of nanocrystalline silver.

Austenitic stainless steel has high potential as nuclear and engineering materials, but it is often coarse grained and has relatively low yield strength, typically 200–400 MPa. We prepared a bulk nanocrystalline lanthanum-doped 304L austenitic stainless steel alloy by a novel technique that combines mechanical alloying and high-pressure sintering. The achieved alloy has an average grain size of 30 ± 12 nm and contains a high density (~1024 m−3) of lanthanum-enriched nanoprecipitates with an average particle size of approx. 4 nm, leading to strong grain boundary strengthening and dispersion strengthening effects, respectively. The yield strength of nano-grained and nano-precipitated stainless steel reaches 2.9 GPa, which well exceeds that of ultrafine-grained (100–1000 nm) and nano-grained (

Low-cost metal sulfides are promising anode materials for sodium-ion batteries (SIBs); however, they suffer from sluggish kinetics and large volume expansion upon cycling. Here, a strategy to grow FeS2 on turbostratic carbon (t-carbon) assisted by chemical interactions between Fe and C electrons was realized via a simple and scalable mechanical alloying (MA) approach with a trace amount of CNTs. The structural change in CNTs synchronized with the in situ growth of FeS2 on the transformed t-carbon during the MA process, forming localised FeS2 nanocrystals wrapped in the frameworks of t-carbon. This intertwined structure within a grain consisted of chemical bonding by electronic hybridization between FeS2 and its adjacent carbon layer, resulting in enhanced structural stability upon cycling. Moreover, the localised FeS2 nanocrystals with an ultrasmall diameter of 10 nm encapsulated in the nanoframeworks of t-carbon could effectively shorten the diffusion paths of electrons/ions and withstand the volume expansion. The as-synthesized FeS2–C hybrid composite electrode exhibited a pseudocapacitive diffusion behavior with high specific capacity, good cycling stability, and remarkable rate capability. This strategy is a facile, scalable, and low-cost route toward high-performance metal sulfide anode materials for the commercial utilization of SIBs.

It is a challenge to obtain high specific capacitance and high energy density for carbon materials applied in energy storage. In this work, a metal-organic framework (MOF) with high surface area (1149 m2 g−1) is used for the design of Co/C nanocomposites. Ni(OH)2@Co/C nanocomposites with core/shell structure are synthesized by carbonizing MOF nanoparticles to form the cores of Co/C and growing 2-dimensional Ni(OH)2 nanosheets on the surfaces, as the shells. The Ni(OH)2@Co/C nanocomposites exhibit excellent electrochemical properties, including high specific capacitance (952 F g−1, 0.5 A g−1), high-rate dischargeability (692 F g−1, 20 A g−1), and good cycle stability (84%, 10000th cycles), being ascribed to the combined effect of the components and the structure characteristics, i.e., Ni(OH)2 ultrathin nanosheets for high capacitance, Co nanoparticles for high rate dischargeability and nanoporous carbon for excellent cycle life. The asymmetric supercapacitor assembled with the Ni(OH)2@Co/C materials and active carbon presents a higher energy density of 33.6 Wh kg−1 at 516.3 W kg−1. The simple but powerful design routine will be beneficial to the application of MOF in such energy storage filed as battery and supercapacitor.

Nitride materials are of considerable interest due to their fundamental importance and practical applications. However, synthesis of transition metal nitrides often requires extreme conditions, e.g., high temperature and/or high pressure, slowing down the experimental discovery. Using global structure search methods in combination with first-principles calculations, we systematically explore the stoichiometric phase space of iron–nitrogen compounds on the nitrogen-rich side at ambient and high pressures up to 100 GPa. Diverse stoichiometries in the Fe–N system are found to emerge in the phase diagram at high pressures. Significantly, FeN4 is found to be stable already at ambient pressure. It undergoes a polymerization near 20 GPa which results in a high energy density. Accompanying the polymerization, FeN4 transforms from a direct band gap semiconductor to ferromagnetic metal. We also predict several phase transitions in FeN and FeN2 at high pressure, and the results explain the previous experimental obse...

Coarse-grained high-entropy alloys (HEAs) have such excellent mechanical properties as high hardness and strength. The well-known Hall-Petch relation suggests that this high hardness should be further increased if the crystallite size of HEAs is decreased to nanometer scale. We prepared single-phased nanocrystalline (NC) refractory VNbMoTaW HEAs powders by mechanical alloying (MA). The achieved NC HEAs have a body-centered cubic (BCC) structure and an average grain size of approx. 6 nm. We further used a high-pressure/high-temperature (HPHT) technique to consolidate the NC powders to achieve bulk NC HEAs. The evolution of phases, microstructure and mechanical properties of the consolidated bulk NC HEAs were studied as a function of consolidating temperature. The bulk NC VNbMoTaW HEAs consolidated at an optimized temperature of 1150 °C have an average grain size of ∼30 nm and a hardness of 11.4 GPa, ∼ twice that of coarse-grained refractory HEAs. This ultrahigh hardness has three origins: solid solution, grain boundary and dislocation hardening.

Carbon dioxide (CO2) as a greenhouse gas causes globe warming. Recent studies have shown that CO2 can be harnessed to make an energy storage device through the operation of metal-CO2 batteries. While the Li-CO2 and Na-CO2 batteries showing high capacity and good cycle life have been demonstrated, the possibility of creating a K-CO2 battery has not been realized. Here we report the creation of a K-CO2 battery by using CO2 as the cathode in an advanced aberration corrected environmental transmission electron microscope, and in-situ observation of the discharge and charge processes of the nanobattery. During discharge, K2CO3 was generated in the cathode, which converted back to metal K during charge, and the K-CO2 nanobattery demonstrates a good cyclability. Moreover, it is evident that CO gas was released during discharge and the carbon cathode was consumed continuously during charge. Our study provides a fundamental understanding of the K-CO2 battery, which may aid the designing of K-CO2 based energy storage devices.

Annealing often causes softening in conventional large-grained materials. However, annealing has been found to cause hardening in many nanocrystalline metals and alloys. This abnormal hardening by annealing has been explained by such factors as solute segregation at grain boundaries, grain boundary relaxation, grain boundary pinning by second phase particles, etc. In the present work, a homogenous single-phase nanocrystalline Ni(Fe) alloy prepared by electrodeposition was investigated. This alloy is with approx. 1 at% Fe and composed of a solid solution of Fe in Ni without any precipitated phase. The goal is to shed light on which mechanism dominates annealing hardening. Microhardness of the alloy was found to increase slightly just before the grains started to grow during annealing. In addition, long time annealing at the hardening temperature resulted in the decrease of hardness due to grain growth. Both lattice parameter and atom probe tomography studies suggest that the annealing hardening is caused by the segregation of solute and impurity atoms on grain boundaries in the nanocrystalline Ni(Fe) alloy.

We report real time imaging of the oxygen reduction reactions (ORRs) in all solid state sodium oxygen batteries (SOBs) with CuO nanowires (NWs) as the air cathode in an aberration-corrected environmental transmission electron microscope under an oxygen environment. The ORR occurred in a distinct two-step reaction, namely, a first conversion reaction followed by a second multiple ORR. In the former, CuO was first converted to Cu2O and then to Cu; in the latter, NaO2 formed first, followed by its disproportionation to Na2O2 and O2. Concurrent with the two distinct electrochemical reactions, the CuO NWs experienced multiple consecutive large volume expansions. It is evident that the freshly formed ultrafine-grained Cu in the conversion reaction catalyzed the latter one-electron-transfer ORR, leading to the formation of NaO2. Remarkably, no carbonate formation was detected in the oxygen cathode after cycling due to the absence of carbon source in the whole battery setup. These results provide fundamental unde...

At room temperature, a large negative out-of-plane magnetoresistance (MR), [R(H)-R(0)]/R(0), with a value of −35.76% at magnetic field of 9 T has been obtained in the cobalt ferrite (CoFe2O4)/polyaniline (PANI) nanocomposites with CoFe2O4 loading of 40.0 wt% prepared by surface initiated polymerization (SIP) method, which is strongly related to the weak localization (WL) model in the weak disordered system. The negative MR at room temperature in the CoFe2O4/PANI nanocomposites exhibits the obvious nanoparticle loading and magnetic field dependent properties. Both thermal activated transport model and Mott variable range hopping (VRH) model are applied to express the electrical transport mechanism for the temperature regimes of 180–290 K and 50–180 K, accordingly. The electrical transport in the CoFe2O4/PANI nanocomposites obeys the 3D VRH transport mechanism at low temperature range of 50–180 K. The estimated activation energy Eg for the CoFe2O4/PANI nanocomposites with different CoFe2O4 nanoparticle loadings of 10.0, 20.0, 40.0, and 60.0 wt% is 61, 63, 65, and 87 meV, respectively. The coating of PANI on the surface of CoFe2O4 nanoparticle reveals the significant effect on both the remanence and coercivity of CoFe2O4 nanoparticle.

Using surface photovoltaic and electric-field-induced surface photovoltaic techniques, as well as a CASTEP simulation method, we have studied the photo-excited and field-induced charge transfer (CT) behaviors of anatase nano-TiO2 particles adsorbed by O2, N2, and water vapor. Our results suggest that the photo-generated carriers transport process is strongly influenced by the adsorbates on the TiO2 nanoparticles. Oxygen molecules enhance the main-band-gap CT transition at 345 nm and inhibit the sub-band-gap CT transition at 419 nm. This can be explained by the 1 π g electrons in adsorbed O2 and the widened bandgap after adsorbing O2. Nitrogen molecules inhibit the main-band-gap and the sub-band-gap CT transitions differently. This can be explained by the 3 σ g and 1 π g electrons of adsorbed N2, which may cause more new surface states in between the bandgap and decrease the valence band edge of nano-TiO2, as suggested by the CASTEP simulation. The influence of adsorbed water molecule on the main-band-gap CT transition is much stronger than that on the sub-band-gap CT transition.

Designing low-cost oxygen reduction reaction (ORR) electrocatalysts to replace platinum group metal holds great promise for boosting the wide use of metal-air batteries. Herein, atomically dispersed iron supported on nitrogen-doped carbon (A-Fe-NC) was fabricated via an effective ligand-stabilized pyrolysis strategy. Owing to the high density of the active sites and the two-dimensional (2-D) nanosheet structure, the as-prepared A-Fe-NC electrocatalyst delivers excellent ORR performance with a positive half-wave potential of 0.865 V in alkaline solution, which is superior to that of Pt/C (0.82 V vs RHE). Moreover, the primary Zn-air battery assembled with the A-Fe-NC delivered an ultrahigh specific power of 132.2 mW cm−2 and stable long-term operation. It also displayed robust charging-discharging cycling performance with voltage gap of 0.83 V after 240 h, lower than that of the Pt/C + RuO2 electrode (0.95 V). To reveal the catalytic mechanism of A-Fe-NC, density functional theory calculation was conducted and the results revealed that the interaction between Fe and nitrogen regulated the electronic structure of active sites, thus improving charge transfer and further promoting the electrocatalytic reactivity for ORR. This work provided a facile and effective strategy for constructing Fe/N codoped 2-D carbon nanocomposite as high performance electrocatalysts for energy conversion.

Nanocrystalline metals, e.g., Mg, are often strong but with a low thermal stability. In this study, six solute elements, Ti, Zr, Ta, Co, Cr, La, which are immiscible in Mg under equilibrium conditions, are mechanically alloyed with Mg to study the extension of solid solubility, the thermal stability and the mechanical properties of nanocrystalline Mg. Extended solid solubility of Ti and Zr solutes in Mg matrix is achieved after mechanical alloying. The nanocrystalline Mg is largely stabilized by Ti, moderately stabilized by Zr, and not stabilized by Ta, Co, Cr and La. The onset temperature for a rapid grain growth increases from 100 °C (0.4 Tm) for nanocrystalline Mg to ~ 350 °C (0.68 Tm) for nanocrystalline Mg0.95Ti0.05 (defined as Mg-5Ti). A relatively small grain size of ~ 145 nm is achieved in Mg-5Ti at 350 °C. The enhanced thermal stability of nanocrystalline Mg-Ti alloy can be attributed to the segregation of Ti atoms at grain boundaries. In addition, an abnormal grain growth is also observed because of the inhomogeneous distribution of solute/impurity atoms. The high thermal stability of nanocrystalline Mg-5Ti alloy enables us to degass the mechanically alloyed powders at a high temperature of 300 °C and achieve a porosity-free nanocrystalline bulk with a compressive yield strength of 183 MPa and a fracture strain of above 0.6.

Nanoparticles have great potentials to improve the strength of metal matrix composites, but unfortunately, they tend to grow at high temperatures and are difficult to disperse uniformly with a high content, limiting the improvement in thermal stability and mechanical properties. Here we show the synthesis and performance of Mg–MgO in situ nanocomposites with a fraction of up to 40 vol% MgO nanoparticles. Our synthetic strategies include reactively cryomilling Mg with oxygen and subsequently consolidating the cryomilled powders under a high pressure of 6 GPa. Dispersed MgO nanoparticles with a fine particle size of 7.8 ± 1.7 nm are mainly situated at grain boundaries and exhibit a strong interfacial bonding with Mg matrix. Because of the strong Zener pinning effect of in situ formed MgO nanoparticles, the thermal stability is largely enhanced from ~ 100 °C for nanocrystalline Mg to 400 °C for Mg–10vol%MgO. The high thermal stability of Mg–MgO enables us to consolidate the cryomilled powders at a high temperature of 500 °C under a pressure of 6 GPa and achieve bulk Mg–MgO nanocomposites with a high compressive yield strength: 562 and 688 MPa for Mg–10vol%MgO and Mg–20vol%MgO, respectively. Meanwhile, the room-temperature hardness of the Mg–MgO nanocomposites increases linearly with the content of MgO nanoparticles and reaches 3.65 GPa for Mg–40vol%MgO. Furthermore, the MgO nanoparticles significantly improve the high-temperature hardness of nanocrystalline Mg.

Ceramics possess high temperature resistance, extreme hardness, high chemical inertness and a lower density compared to metals, but there is currently no technology that can produce satisfactory joints in ceramic parts and preserve the excellent properties of the material. The lack of suitable joining techniques for ceramics is thus a major road block for their wider applications. Herein we report a technology to weld ceramic nanowires, with the mechanical strength of the weld stronger than that of the pristine nanowires. Using an advanced aberration-corrected environmental transmission electron microscope (ETEM) under a CO2 environment, we achieved ceramic nanowelding through the chemical reaction MgO + CO2 → MgCO3 by using porous MgO as the solder. We conducted not only nanowelding on MgO, CuO, and V2O5 nanowires and successfully tested them in tension, but also macroscopic welding on a ceramic material such as SiO2, indicating the application potential of this technology in bottom-up ceramic tools and devices., Fabricating complex nanodevices requires joining techniques such as welding, common for metals but still out of reach for ceramics. Here the authors use MgO as a solder in a transmission electron microscope with a CO2 atmosphere to weld ceramic nanowires, and show their novel technique can also weld bulk ceramics.

In this work, nano-structured Mn3O4 particles with spongy-morphology were synthesized through vesicle templating, where hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as cationic-anionic surfactants. The Mn3O4 electrode materials exhibited a high specific capacitance (451 F g−1) at a current density of 0.5 A g−1 in 1 mol L−1 Na2SO4 electrolyte, and retained 333 F g−1 when the current density was increased to 5 A g−1. Its capacitance retention is also high (up to 92%) after 10,000 cycles at a current density of 5 A g−1.

A local structure determines the properties in disordered solid solutions with simple crystal structure. Introducing a weak enthalpy-interaction-element will change the local structure evolution of refractory high-entropy alloy films, thereby bringing effects for the properties. Herein series of (NbMoTaW)100-xVx (x = 0 ~ 30.5, at%) thin films were prepared by radio frequency magnetron sputtering, and systematic investigations of the films are carried out through combining the underlying microstructure, mechanical properties, and resistivity-temperature behavior. Furtherly, in accordance with the cluster-plus-glue-atom model, the present paper interpreted the local structure evolution with the film components changing. The results reveal that the excellent thermal stability of the films is originate from the enthalpy interaction, and the high stability of the refractory element itself. The V addition is free of crystal structure variation in the films, but bringing two-fold effects. The main one is the enhancement of the microstructural homogeneity by increasing the disorder degree. The other is weakening interatomic interactions as well as enabling the films more unstable due to the increasing system energy. The refractory high-entropy films can be promising candidates for high temperature, high hardness, and wear-resistance applications, e.g., high-temperature-bearing structures, heat-protection systems, diffusion barriers, and film resistors.

The photogenerated carriers’ transport and microstructure of self-assembled core–shell ZnSe/ZnS/L-Cys quantum dots (QDs), which was synthesized at room temperature, are studied via the surface photovoltaic and transient photovoltaic techniques, X-ray diffraction, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet–visible absorption spectra. The results suggest that the ZnSe nanocrystals prepared at room temperature prefer to nucleate at (111) and (220) faces, and grow a shell–ZnS at (220) face rather than at (311) face. The quantum well depth in some interface space charge region (SCR) of the QDs prepared at room temperature is smaller than that prepared at 90 °C. The evolution of the band bending from a depletion layer to an accumulation layer may occur in the graded-band-gap and at the side of the interface SCR, as compared the QDs with p-type photovoltaic characteristic synthesized at room temperature to that at 90 °C. This electron structural shift may be ascribed to the reduced quantum well depth and then an obvious resonance quantum tunneling of the QDs synthesized at room temperature.

One of the fundamental magnetic properties – the low-temperature magnetization as well as the exchange interactions derived by using a spin-wave excitation theory – has been well studied in glassy ribbons rather than bulk metallic glasses. The paper studies the temperature-dependent magnetization of a bulk Fe 40 Ni 40 P 14 B 6 alloy, derives the range and fluctuation of exchange interactions, and compares these magnetic behaviors with those of well-studied glassy ribbons. The low-temperature magnetization of our bulk glass can be well expressed by a spin-wave excitation theory, which has been widely utilized to study the temperature-dependent magnetization of ferromagnetic glassy ribbons. Moreover, both the derived spin-wave stiffness coefficient and the derived range and fluctuation of exchange interactions in our bulk metallic glass are very similar to those in glassy ribbons, indicative of the similarity in magnetic exchange interaction between bulk metallic glasses and glassy ribbons.

We developed a method to make CNTs fully coated by polyvinylpyrrolidone (PVP), which acts as an agent to effectively combine CNTs and LiFePO 4 to form a nanocomposite. In this nanocomposite, unbreaking and non-entangling CNTs forms a highly conductive 3D CNTs network that can significantly improve both the electrical conductivity of LiFePO 4 and the diffusion coefficient of Li ions and electrons. As a result, our CNTs/LiFePO 4 nanocomposite exhibited an excellent high-rate capacity and an ultralong cycling stability, i.e., a high discharge capacity of 123 mAh g −1 and an extremely low loss in capacity of 1.6% could be achieved after 1000 cycles at 10C. A capacity of ∼100 mAh g −1 (corresponding to a capacity retention of 80%) could still be achieved after 3400 cycles at 10C. The loss in capacity of our LiFePO 4 /CNTs is ∼four to eight times smaller than that of previously studied LiFePO 4 /CNTs and LiFePO 4 /graphene nanocomposites. Our simple but powerful synthetic techniques should be beneficial to the application of lithium-ion batteries based on LiFePO 4 electrode materials in such electric vehicles as PHEVs, AEVs, and HEVs.

Bulk metallic glasses (BMGs) have an extremely low coercivity, suggesting that the BMGs must have unique magnetic microstructures. These magnetic microstructures, however, are largely unknown. We prepared Fe65.5Cr4Mo4Ga4P12B5.5C5 BMGs by a flux-melting and water-quenching technique. We then studied the topographical and magnetic microstructures of as-quenched and annealed BMGs by atomic force microscopy (AFM) and magnetic force microscopy (MFM), respectively. The microstructural results were compared with those achieved in rapidly quenched glassy ribbons. Magnetic domains are pinned inside the BMGs due to residual stress, most of which can be removed by annealing. This is also applicable to the glassy ribbons. However, when compared to the glassy ribbons, our BMGs are with a significantly smaller surface roughness, a much smaller free volume, and free from non-magnetic inclusions. It is these unique microstructural factors and the stress release by annealing that greatly improve the soft ferromagnetic properties of our iron-based BMGs.

Achieving high strength with heat resistance is a critical issue for Mg alloys. In the present study, we have successfully designed a novel hierarchical long-period stacking ordered (LPSO) architecture in the Mg-Y-Zn based alloy. The hierarchical LPSO is featured by a heterogeneous microstructure of ultra-fine grained (UFG) LPSO matrix and discrete LPSO lath domains at the microscale, and high-density in-situ Y-O-Si nano-dispersoids decorating the UFG-LPSO matrix at the nanoscale. The in-situ precipitation of nano-dispersoids in LPSO phase has been achieved for the first time to date. The hard UFG-LPSO matrix decorated with high-density stiff nano-dispersoids delivers the high thermal stability and ultrahigh strength of the alloys at both room and elevated temperatures, where the alloy with a UFG-LPSO fraction of ~71% acquires ultrahigh yield strength of 795 MPa and 428 MPa at room temperature and 250 °C, respectively. In addition, the elevated-temperature strength can be further improved after extrusion via texture strengthening. Meanwhile, the soft LPSO lath domains in the heterogeneous microstructure undertake the plastic deformation via kinking, contributing to the compressive plasticity at room temperature. The ultrahigh strength, thermal stability combined with low density and excellent specific properties of the present hierarchical LPSO alloys demonstrate a potential microstructural strategy to design lightweight high-strength Mg alloys for advanced structural applications.

As structural materials candidates of advanced fission and future fusion reactors, oxide-dispersion-strengthened (ODS) alloys, which are often ultrafine-grained (with a grain size between 100 and 1000 nm), have attracted widespread interest in past decades. However, fabrication of fully dense bulk nanocrystalline ODS alloys has rarely been reported. In this work, a novel Zr-doped nanocrystalline 14YWTZ ferritic ODS alloy (Fe–14Cr–3W-0.4Ti-0.8Zr-0.3Y2O3) was prepared by mechanical alloying and high-pressure consolidation techniques. The high consolidation pressure (4 GPa) endows the bulk nanocrystalline 14YWTZ alloy with a nearly full relative density (~99.5%) and a reasonable tensile elongation. The consolidated nanocrystalline 14YWTZ alloy with an average grain size of ~50 nm shows an ultra-high compressive yield strength of ~2641 MPa. Besides, the alloy exhibits an exceptional thermal stability, i.e., limited grain growth occurs after annealing at a high temperature of 1000 °C. After hot rolling, the alloy retains nanocrystalline microstructures and exhibits an unprecedented tensile yield strength of 2730 MPa, far exceeding those of previous reported ferritic ODS alloys. The high thermal stability of the annealed nanocrystalline 14YWTZ alloys can be ascribed to the combined effects of the thermodynamic multicomponent co-segregation to grain boundaries and strong kinetic Zener pinning by high-density Zr–Ti–Y–O-enriched nanoparticles with an average particle size of ~3.18 nm and a high number density of ~3 × 1024 m−3. The outstanding strength of the present nanocrystalline 14YWTZ alloys primarily originates from the Hall-Petch strengthening of the nanocrystalline matrix, distinguishing them from conventional ODS alloys strengthened by dislocation forest and/or dispersed oxide nanoparticles.

Helium accumulation in advanced nuclear systems would accelerate the failure of structural materials. Nanostructured materials have the potential to mitigate helium effects by providing more nucleation sites for He bubbles. La-doped nanocrystalline 304 austenitic stainless steel (NC304-La) possesses ultra-fine and stable nano-grains ~45 nm in diameter and high-density fine nano-precipitates. In this work, we implanted NC304-La with helium ions, then annealed at different temperatures after implantation. We found that combining the key features of nanocrystalline steels and oxide dispersion-strengthened steels, NC304-La showed excellent bubble swelling resistance. We characterized the interaction between He bubbles and the two features in NC304-La: grain boundaries and nano-precipitates. Through detailed study for the heat-treatment related behaviors of He bubbles in this multi-sink system, the mechanisms of He bubble coarsening resistance in NC304-La were proposed.

Ti-Mg composites have been successfully fabricated by a novel high-pressure solid-state sintering technique, by which simultaneous solid-state sintering of the low-melting-point Mg with the high-melting-point Ti is achieved at a high temperature of upto 1000 °C under a high pressure of 4 GPa. The well-sintered composites with a fully dense microstructure exhibit a continuous Ti matrix and a strong interfacial bonding, which are difficult to achieve by other sintering methods. Meanwhile, both Ti-Mg composites and the derived porous Ti exhibit superior mechanical properties, demonstrating promising prospect for load-bearing implant applications.

Mesoporous Ni(OH)2/Co(OH)2 electrode materials were synthesized via a simple one-pot procedure by combining homogeneous precipitation and stepwise precipitation method. The configuration of the porous Ni(OH)2/Co(OH)2 electrode materials synthesized provides 3D electron transmission channels through a high conductive Co(OH)2 distributed in the peripheral nanolayer of the composites, which is beneficial to rate capability and cycle stability. The Ni(OH)2/Co(OH)2 electrode materials have a specific surface area of 229 m2 g−1, which is approximately 40% higher than that of Ni(OH)2 (163 m2 g−1). Their specific capacitance is up to 1202 and 1022 F g−1 at the current densities of 10 and 20 A g−1, respectively. Furthermore, the capacitance retention of the electrode materials at the current density of 10 A g−1 is 98% after 5000 cycles. The synthesis method provides a novel simple route to fabricate heterostructure materials for capacitors with high electrochemical performance.

A novel biomorphic heteroatom-doped porous carbon with 2.86% of nitrogen and 12.36% of oxygen is synthesized by using a mold (Rhizoctonia Solani Kuhn) as the precursor. The biomorphic porous carbon electrode material exhibits an ultra-high volumetric capacitance of up to 655 F cm−3 at current density of 0.5 A g−1 and superior cycle stability of 100% after 10,000 cycles at a current density of 10 A g−1. This work provides a new approach to obtain biomass with low cost, no pollution, short production cycle and high yield. Furthermore, the genetic stability is more beneficial for the formation of the uniform architecture and composition.

Nanocrystalline metals are often strong but with a low thermal stability. In this study, a bulk nanocrystalline Mg-1.5at%Ti alloy with a high thermal stability is successfully fabricated by mechanical alloying and subsequent high-temperature/high-pressure consolidation. The rapid grain growth of nanocrystalline Mg and Mg-1.5at%Ti alloy starts at ∼100 °C (0.40 T m ) and 450 °C (0.78 T m ), respectively. The high thermal stability of nanocrystalline Mg-1.5at%Ti alloy can be attributed to the segregation of Ti atoms at grain boundaries. The high thermal stability of nanocrystalline Mg-Ti alloy enables us to consolidate the alloy powders at a high temperature of 400 °C (0.73 T m ) under a pressure of 4 GPa, yielding a bulk nanocrystalline Mg-Ti alloy with a high strength of 202 MPa and a large fracture strain of above 0.8.

Bulk nanocrystalline (NC) boron-doped refractory (VNbMoTaW)99B1 high entropy alloys (HEAs) were fabricated by mechanical alloying (MA) and high-pressure/high-temperature consolidation techniques. The consolidation was carried out between 800 and 1500 °C to examine the evolution of crystal phases, microstructure and mechanical performance. The bulk NC (VNbMoTaW)99B1 HEAs consolidated at 1350 °C are composed of a matrix with an average grain size of 43 nm and boride and carbide nanoprecipitates with an average particle size of 17 nm. The bulk NC (VNbMoTaW)99B1 HEAs exhibit ultrahigh hardness of 16.3 GPa (approx. triple that of their coarse-grained (CG) counterparts), an ultrahigh yield strength of 5.7 GPa (approx. five times that of their CG counterparts) under compression, and a total engineering strain of approx. 10%. The ultrahigh hardness and strength have four origins: solid solution, precipitation, grain boundary, and dislocation strengthening. The room-temperature resistivity of bulk NC (VNbMoTaW)99B1 is as high as ∼ 387 μΩ·cm, approx. five times that of their CG counterparts. This high resistivity can be related to the high volume fractions of grain boundaries and phase interfaces, the point defects and dislocations near grain boundaries, and the severe lattice distortions.

Nanocrystalline Mg is often strong but with a low thermal stability. Herein, a Mg-MgF2 nanocomposite is successfully fabricated by reactive milling. The thermal stability is largely enhanced from ∼100 °C for nanocrystalline Mg to ∼450 °C for Mg-MgF2. The bulk Mg-MgF2 nanocomposite consolidated at a high temperature of 500 °C under 6 GPa exhibits a high compressive yield strength of 582 MPa. Meanwhile, the MgF2 nanoparticles significantly improve the high-temperature hardness of nanocrystalline Mg. The fine, dispersed and thermally stable MgF2 nanoparticles with a strong interfacial bonding with the matrix are the microstructural features that dominate the superior properties – high thermal stability and high strength at room and elevated temperatures.

Co3O4 nano materials have attracted tremendous attention as effective catalysts for sodium oxygen batteries (SOBs). However, their electrochemical processes and fundamental catalytic mechanism remain unclear till now. Herein, in-situ environmental transmission electron microscopy technique was used to study the catalysis mechanism of the Co3O4 nanocubes in SOBs during discharge and charge processes. It is found that during the 1st discharge and charge processes, Na2O2 formed and decomposed, respectively, around the Co3O4 nanocubes, but the following discharge and charge processes were very difficult. In order to promote the charge kinetics, we increased the charging temperature up to 500 °C, when the decomposition of Na2O2 became facile. Aberration corrected high-angle annular dark field imaging indicated that a thin layer of CoO grew epitaxially on the surface of Co3O4 nanocubes after the first discharge. Density functional theory calculations indicate that the CoO surface is energetically more favorable than Co3O4 for the nucleation of Na2O2. This study provides not only new fundamental understandings to the electrochemical reaction mechanisms of SOBs, but also strategies to improve the cycling performance of solid state SOBs.

Magnetic high-entropy alloys (HEAs) can be processed to have a relatively high saturation magnetization (or induction), but usually exhibit a relatively high coercivity of above 200 A/m. In addition, although a high electrical resistivity of magnetic HEAs makes them attractive for manufacturing energy-saving high-frequency magnetic devices, the critical application-oriented magnetism, i.e., the frequency- and induction-dependent power loss, of magnetic HEAs is largely unknown. Here, we report the (Co30Fe45Ni25)1-x(Al40Si60)x HEAs with exceptional mechanical, electrical, and magnetic performance. The magnetic (Co30Fe45Ni25)0.8(Al40Si60)0.2 HEA has a single-phased body-centered-cubic (BCC) structure, a high yielding strength of 1,636 MPa, and a high electrical resistivity ( R ) of 68.0 μΩ cm. This magnetic HEA also has the best combination of induction and coercivity reported so far: a high saturation induction ( B s ) of 1.24 Tesla and a low coercivity ( H c ) of only 59.7 A/m. Furthermore, the dependence of total power loss on both frequency and induction is investigated. The contribution of hysteresis loss, eddy-current loss, and abnormal loss to the total power loss is also studied. The abnormal loss is comparable to the eddy-current loss in both Fe-Si and magnetic HEAs. For a frequency above approx. 200 Hz, the total power loss of the (Co30Fe45Ni25)0.8(Al40Si60)0.2 HEA is lower than that of conventional Fe-Si alloys. This trend is mainly because the eddy-current loss of HEA is lower than that of conventional Fe-Si alloys.

Nanocrystalline (NC) metals are stronger and more radiation-tolerant than their coarse-grained (CG) counterparts, but they often suffer from poor thermal stability as nanograins coarsen significantly when heated to 0.3 to 0.5 of their melting temperature (Tm). Here, we report an NC austenitic stainless steel (NC-SS) containing 1 at% lanthanum with an average grain size of 45 nm and an ultrahigh yield strength of ~2.5 GPa that exhibits exceptional thermal stability up to 1000 °C (0.75 Tm). In-situ irradiation to 40 dpa at 450 °C and ex-situ irradiation to 108 dpa at 600 °C produce neither significant grain growth nor void swelling, in contrast to significant void swelling of CG-SS at similar doses. This thermal stability is due to segregation of elemental lanthanum and (La, O, Si)-rich nanoprecipitates at grain boundaries. Microstructure dependent cluster dynamics show grain boundary sinks effectively reduce steady-state vacancy concentrations to suppress void swelling upon irradiation., Weaker ferritic/matensitic steels rather than stronger austenitic steels are usually candidates for nuclear reactors since they do not easily swell under irradiation. Here, the authors make an ultrastrong lanthanum-doped nanocrystalline austenitic steel that is thermally stable and radiation-tolerant.

Lithium metal is an ideal anode for next-generation lithium batteries owing to its very high theoretical specific capacity of 3860 mAh g-1 but very reactive upon exposure to ambient air, rendering it difficult to handle and transport. Air-stable lithium spheres (ASLSs) were produced by electrochemical plating under CO2 atmosphere inside an advanced aberration-corrected environmental transmission electron microscope. The ASLSs exhibit a core-shell structure with a Li core and a Li2 CO3 shell. In ambient air, the ASLSs do not react with moisture and maintain their core-shell structures. Furthermore, the ASLSs can be used as anodes in lithium-ion batteries, and they exhibit similar electrochemical behavior to metallic Li, indicating that the surface Li2 CO3 layer is a good Li+ ion conductor. The air stability of the ASLSs is attributed to the surface Li2 CO3 layer, which is barely soluble in water and does not react with oxygen and nitrogen in air at room temperature, thus passivating the Li core.

Metallic materials subjected to heavy ion irradiation experience significant radiation damage. Free surface is a type of effective defect sinks to improve the radiation resistance in metallic materials. However, the radiation resistance of metallic nanowires (NWs) is largely unknown. Here we show, via in situ Kr ion irradiations in a transmission electron microscope, Ag NWs exhibited much better radiation resistance than coarse-grained Ag. Irradiation-induced prominent surface roughening in Ag NWs provides direct evidence for interaction between defect clusters and free surface. Diameter dependent variation of the surface roughness in irradiated Ag NWs has also been observed. This study provides insight on mechanisms of enhanced radiation resistance via free surfaces in metallic NWs.

Power loss – one of the important application-oriented magnetic properties of ferromagnetic metallic glasses – has been well studied in glassy ribbons rather than bulk metallic glasses. This paper studies the influence of frequency, induction, annealing, and specimen thickness on the total power loss – which is divided into hysteresis loss, classical eddy current loss, and excess eddy current loss – of bulk ferromagnetic Fe 65.5 Cr 4 Mo 4 Ga 4 P 12 B 5.5 C 5 glasses. The total power loss of bulk glasses increases with frequency and peak induction and follows a power relation, similar to what has been observed in glassy ribbons. Annealing decreases both the hysteresis loss and the classical eddy current loss, resulting in a lower total power loss. The ratio of excess eddy current loss to classical eddy current loss deceases with increasing specimen thickness. The excess eddy current loss is negligible for our thickest glass and comparable to the classical eddy current loss for our thinner glasses. In contrast, the excess eddy current loss is often at least one to two orders of magnitude greater than the classical eddy current loss in glassy ribbons. The low total power loss achieved in bulk ferromagnetic glasses should be beneficial to their practical applications in energy conversion devices.

Developing cost-effective soft magnetic alloys with excellent mechanical properties is very important to energy-saving industries. This study investigated the magnetic and mechanical properties of a series of (Fe0.3Co0.5Ni0.2)100&minus, x(Al1/3Si2/3)x high-entropy alloys (HEAs) (x = 0, 5, 10, 15, and 25) at room temperature. The Fe0.3Co0.5Ni0.2 base alloy composition was chosen since it has very the smallest saturation magnetostriction coefficient. It was found that the (Fe0.3Co0.5Ni0.2)95(Al1/3Si2/3)5 alloy maintains a simple face-centered cubic (FCC) solid solution structure in the states of as-cast, cold-rolled, and after annealing at 1000 &deg, C. The alloy after annealing exhibits a tensile yield strength of 235 MPa, ultimate tensile strength of 572 MPa, an elongation of 38%, a saturation magnetization (Ms) of 1.49 T, and a coercivity of 96 A/m. The alloy not only demonstrates an optimal combination of soft magnetic and mechanical properties, it also shows advantages of easy fabrication and processing and high thermal stability over silicon steel and amorphous soft magnetic materials. Therefore, the alloy of (Fe0.3Co0.5Ni0.2)95(Al1/3Si2/3)5 holds good potential as next-generation soft magnets for wide-range industrial applications.

The Drude model modified by Debye relaxation time was introduced to determine the plasma frequency (ωp) in the surface initiated polymerization (SIP) synthesized β-silicon carbide (β-SiC)/polyaniline (PANI) metacomposites. The calculated plasma frequency for these metacomposites with different loadings of β-SiC nanoparticles was ranging from 6.11 × 10(4) to 1.53 × 10(5) rad s(-1). The relationship between the negative permittivity and plasma frequency indicates the existence of switching frequency, at which the permittivity was changed from negative to positive. More interestingly, the synthesized non-magnetic metacomposites, observed to follow the 3-dimensional (3-D) Mott variable range hopping (VRH) electrical conduction mechanism, demonstrated high positive magnetoresistance (MR) values of up to 57.48% and high MR sensitivity at low magnetic field regimes.

Nanostructured materials have great potential for use as structural materials in advanced nuclear reactors due to the high density of grain boundaries that can serve as sinks to absorb irradiation-induced defects. In the present study, the irradiation tolerance of a La-doped nanocrystalline 304 austenitic stainless steel (NC-La) with a grain size of about 40 nm was investigated under an irradiation of 6 MeV Au ions to 1.5 × 1016 ions cm−2 at 600 °C and room temperature. Compared to its coarse-grained counterpart, in La-doped nanocrystalline steel no visible voids were observed at high-temperature irradiation, and no significant difference in extended defects, such as irradiation-induced dislocation loops or clusters, were found between irradiated and unirradiated areas at room temperature irradiation. Furthermore, the nano grain remains stable under irradiation, and no significant grain growth occurs at both irradiation temperatures. The excellent irradiation tolerance of the La-doped nanocrystalline alloys is attributed to the abundant grain boundaries and enhanced stability of nano grains induced by the Zener pinning effect and La segregation on grain boundaries. This study therefore demonstrates the superior irradiation tolerance of the La-doped nanocrystalline steel.

Nanostructured Cu/304 stainless steel (SS) multilayers were prepared by magnetron sputtering. 304SS has a face-centered-cubic (fcc) structure in bulk. However, in the Cu/304SS multilayers, the 304SS layers exhibit the fcc structure for layer thickness of ≤5 nm in epitaxy with the neighboring fcc Cu. For 304SS layer thickness larger than 5 nm, body-centered-cubic (bcc) 304SS grains grow on top of the initial 5 nm fcc SS with the Kurdjumov-Sachs orientation relationship between bcc and fcc SS grains. The maximum hardness of Cu/304SS multilayers is about 5.5 GPa (factor of two enhancement compared to rule-of-mixtures hardness) at a layer thickness of 5 nm. Below 5 nm, hardness decreases with decreasing layer thickness. The peak hardness of fcc/fcc Cu/304SS multilayer is greater than that of Cu/Ni, even though the lattice-parameter mismatch between Cu and Ni is five times greater than that between Cu and 304SS. This result may primarily be attributed to the higher interface barrier stress for single-dislocation transmission across the {111} twinned interfaces in Cu/304SS as compared to the {100} interfaces in Cu/Ni.

The photoelectron characteristics and nano-doping mechanism of Cu-doped ZnSe/ZnS/L-cys self-assembled core-shell quantum dots (QDs) are studied by surface photovoltaic (SPV) and photoacoustic (PA) techniques, XRD, HRTEM, FT-IR, UV-VIS adsorption, and Laser Raman spectra. The results suggest that the doped copper element prefers to locate at the Zn atom-vacancy of the (111) face of the QDs in the Cu2+ ion form. The defect-state levels are referred to the shallow accepter levels, leading to an obvious quantum confinement effect and a weakened n-type surface photovoltaic characteristic in the Cu-doped QDs. The quantum confinement effect strongly depends on the depth of the quantum well that is buried in the space charge region located in the graded-band-gap and at the side of the core-ZnSe. These electron structures are responsible for the increased lifetime and diffusion length of photogenerated free charge carriers, which significantly enhance the intensity of SPV response, enlarge the range of SPV respons...