Junliang Liu

A wide range of technologies rely on permanent magnets, including levitation devices, motors, generators and magnetic separators. Replacing permanent magnets with bulk superconductors will enable a step change in performance by providing an order of magnitude increase in the achievable magnetic field. However, the reliable fabrication of large single grained superconducting materials with a high, homogeneously distributed magnetic trapped field remains a barrier to the widespread application of these materials. Limits to the size and geometry of RE–Ba–Cu–O single grain bulk superconductors could be overcome by developing a reliable process to assemble larger components by fabricating superconducting joints between smaller samples. In this work we propose a mechanism of joint formation in GdBCO–Ag bulk superconductors using a YBCO–Ag intermediate that is based on detailed analysis of the joint interfaces. This improved understanding of the joint formation process provides the knowledge required to fully optimise the fabrication parameters, and to produce joints with improved superconducting and mechanical properties.

Refractory high-entropy alloys (RHEAs) are emerging materials with potential for use under extreme conditions. As a newly developed material system, a comprehensive understanding of their long-term stability under potential service temperatures remains to be established. This study examined a titanium-vanadium-niobium-tantalum alloy, a promising RHEA known for its superior high-temperature strength and room-temperature ductility. Using a combination of advanced analytical microscopies, Calculation of Phase Diagrams (CALPHAD) software, and nanoindentation, we investigated the evolution of its microstructure and mechanical properties upon aging at 700°C. Trace interstitials such as oxygen and nitrogen, initially contributing to solid solution strengthening, promote phase segregation during thermal aging. As a result of the depletion of solute interstitials within the metal matrix, a progressive softening is observed in the alloy as a function of aging time. This study, therefore, underscores the need for a better control of impurities in future development and application of RHEAs.

Non-oxide ceramics exhibit significant advantages in high-tech industry, but their applications have been limited by the brittle nature especially at low to moderate temperatures. It is a great challenge to improve the ceramic plasticity while maintaining the high-temperature strength through the classical strategy, which generally includes decreasing grain size to several nanometers or adding ductile binder phase. Herein, the plasticity of fully dense boron carbide (B₄C) has been greatly enhanced due to the boundary non-stoichiometry induced by high-pressure sintering technology. The effect decreased the plastic deformation temperature of B₄C by 200°C compared to that of conventionally-sintered specimens. Promoted grain boundary diffusion is found to enhance grain boundary sliding, which dominate the lower-temperature plasticity. In addition, the as-produced specimen maintained extraordinary strength before the occurrence of plasticity. The study provides a new and efficient strategy by boundary chemical change to facilitate the plasticity of ceramic materials.

β-Ga2O3 was suggested to have excellent irradiation hardness which makes β-Ga2O3-based devices extremely attractive for nuclear and space applications. To discern the fundamental nano-scale structural changes with irradiation, an in situ irradiation experiment in a transmission electron microscope was carried out using 400 keV Ar ions of fluences up to 8 × 1015 cm−2 (equivalent to four displacements per atom). Contrary to previous works, which indicate a phase transition of β-Ga2O3 into the κ polymorph, the β-Ga2O3 structure was found to remain intact throughout except for (i) anisotropic lattice distortions, which are most significant at low levels of irradiation, and (ii) the appearance of additional weak reflections above 2 dpa irradiation. The origin of the extra reflections is discussed.

To match the high capacity of metallic anodes, all-solid-state batteries (ASSBs) re- quire high energy density, long-lasting composite cathodes such as Ni-Mn-Co (NMC)- based lithium oxides mixed with a solid-state electrolyte (SSE). However in practice, cathode capacity typically fades due to NMC cracking and increasing NMC/SSE in- terface debonding because of NMC pulverization, which is only partially mitigated by the application of a high cell pressure during cycling. Using smart processing proto- cols we report a single crystal particulate LiNi0.83Mn0.06Co0.11O2 and Li6PS5Cl SSE composite cathode with outstanding discharge capacity of 210 mAh g−1 at 30 °C. A first cycle coulombic efficiency of >85%, and >99% thereafter, was achieved despite a 5.5% volume change during cycling. A near-practical discharge capacity at a high areal capacity of 8.7 mAh cm−2 was obtained using a novel asymmetric anode/cathode cycling pressure of only 2.5 MPa/0.2 MPa.

The solid electrolyte interphase (SEI), a complex layer that forms over the surface of electrodes exposed to battery electrolyte, has a central influence on the structural evolution of the electrode during battery operation. For lithium metallic anodes, tailoring this SEI is regarded as one of the most effective avenues for ensuring consistent cycling behavior, and thus practical efficiencies. While fluoride‐rich interphases in particular seem beneficial, how they alter the structural dynamics of lithium plating and stripping to promote efficiency remains only partly understood. Here, operando liquid‐cell transmission electron microscopy is used to investigate the nanoscale structural evolution of lithium electrodeposition and dissolution at the electrode surface across fluoride‐poor and fluoride‐rich interphases. The in situ imaging of lithium cycling reveals that a fluoride‐rich SEI yields a denser Li structure that is particularly amenable to uniform stripping, thus suppressing lithium detachment and isolation. By combination with quantitative composition analysis via mass spectrometry, it is identified that the fluoride‐rich SEI suppresses overall lithium loss through drastically reducing the quantity of dead Li formation and preventing electrolyte decomposition. These findings highlight the importance of appropriately tailoring the SEI for facilitating consistent and uniform lithium dissolution, and its potent role in governing the plated lithium's structure.

Secondary Ion Mass Spectrometry is an important technique for the study of the composition of a wide range of materials because of the exceptionally high sensitivity that allows the study of trace elements and the ability to distinguish isotopes that can be used as markers for reactions and transport processes. However, when studying nuclear materials, it is often necessary to analyse highly radioactive samples, and only rather few SIMS facilities are available in active environments. In this paper, we present a methodology using focussed ion beam milling to prepare samples from radioactive specimens that are sufficiently large to undertake SIMS mapping experiments over microstructurally significant regions, but with overall activities small enough to be readily transported and analysed by a SIMS instrument in a normal laboratory environment. Radioactive samples prepared using this methodology can also be used for correlative SIMS analysis with other analytical microscopies. SIMS results showing the distributions of deuterium in oxides on in‐reactor corroded zirconium alloys are presented to demonstrate the potential of this sample preparation technique.

Secondary Ion Mass Spectrometry is an important technique for the study of the composition of a wide range of materials because of the exceptionally high sensitivity that allows the study of trace elements and the ability to distinguish isotopes that can be used as markers for reactions and transport processes. However, when studying nuclear materials, it is often necessary to analyse highly radioactive samples, and only rather few SIMS facilities are available in active environments. In this paper, we present a methodology using focussed ion beam milling to prepare samples from radioactive specimens that are sufficiently large to undertake SIMS mapping experiments over microstructurally significant regions, but with overall activities small enough to be readily transported and analysed by a SIMS instrument in a normal laboratory environment. Radioactive samples prepared using this methodology can also be used for correlative SIMS analysis with other analytical microscopies. SIMS results showing the distributions of deuterium in oxides on in‐reactor corroded zirconium alloys are presented to demonstrate the potential of this sample preparation technique.

MgB₂ pellets containing a nanoscale dispersion of artificial pinning centres have been successfully manufactured through a powder metallurgy route based on the oxide dispersion strengthened (ODS) concept more usually used for steels and superalloys. Commercial MgB₂ powder and Y₂O₃ nano-powder were mechanically alloyed in a high energy planetary ball mill and consolidated using the field assisted sintering technique. The composite powders were ball milled for different times up to 12 h and characterised by means of particle size analysis, x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The microstructure and superconducting properties were characterised by density, XRD, STEM and magnetic property measurements. The powder microstructure comprised Y₂O₃ particles dissolved into the MgB₂ matrix. After consolidation there was a near-uniform dispersion of precipitated YB₄ and MgO particles. A bulk 0.5 wt% Y₂O₃-MgB₂ composite showed the best superconducting performance with a significant improvement in J _c at high field compared with unmodified MgB₂, and only a small reduction in T _c . The results suggest that the ODS concept is promising to improve the superconducting properties of MgB₂.

MgB₂ pellets containing a nanoscale dispersion of artificial pinning centres have been successfully manufactured through a powder metallurgy route based on the oxide dispersion strengthened (ODS) concept more usually used for steels and superalloys. Commercial MgB₂ powder and Y₂O₃ nano-powder were mechanically alloyed in a high energy planetary ball mill and consolidated using the field assisted sintering technique. The composite powders were ball milled for different times up to 12 h and characterised by means of particle size analysis, x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The microstructure and superconducting properties were characterised by density, XRD, STEM and magnetic property measurements. The powder microstructure comprised Y₂O₃ particles dissolved into the MgB₂ matrix. After consolidation there was a near-uniform dispersion of precipitated YB₄ and MgO particles. A bulk 0.5 wt% Y₂O₃-MgB₂ composite showed the best superconducting performance with a significant improvement in J _c at high field compared with unmodified MgB₂, and only a small reduction in T _c . The results suggest that the ODS concept is promising to improve the superconducting properties of MgB₂.

Ionic liquids have been shown to stabilize organic-inorganic perovskite solar cells with metal oxide carrier-transport layers, but they are incompatible with more readily processible organic analogs. Lin et al. found that an ionic solid, a piperidinium salt, enhanced the efficiency of positive-intrinsic-negative layered perovskite solar cells with organic electron and hole extraction layers. Aggressive aging testing showed that this additive retarded segregation into impurity phases and pinhole formation in the perovskite layer.

Science , this issue p. 96

High-resolution SIMS analysis can be used to explore a wide range of problems in material science and engineering materials, especially when chemical imaging with good spatial resolution (50–100 nm) can be combined with efficient detection of light elements and precise separation of isotopes and isobaric species. Here, applications of the NanoSIMS instrument in the analysis of inorganic materials are reviewed, focusing on areas of current interest in the development of new materials and degradation mechanisms under service conditions. We have chosen examples illustrating NanoSIMS analysis of grain boundary segregation, chemical processes in cracking, and corrosion of nuclear components. An area where NanoSIMS analysis shows potential is in the localization of light elements, in particular, hydrogen and deuterium. Hydrogen embrittlement is a serious problem for industries where safety is critical, including aerospace, nuclear, and oil/gas, so it is imperative to know where in the microstructure hydrogen is located. By charging the metal with deuterium, to avoid uncertainty in the origin of the hydrogen, the microstructural features that can trap hydrogenic species, such as precipitates and grain and phase boundaries, can be determined by NanoSIMS analysis on a microstructurally relevant scale.