High-entropy ceramics (HECs) are solid solutions of inorganic compounds with one or more Wyckoff sites shared by equal or near-equal atomic ratios of multi-principal elements. Although in the infant stage, the emerging of this new family of materials has brought new opportunities for material design and property tailoring. Distinct from metals, the diversity in crystal structure and electronic structure of ceramics provides huge space for properties tuning through band structure engineering and phonon engineering. Aside from strengthening, hardening, and low thermal conductivity that have already been found in high-entropy alloys, new properties like colossal dielectric constant, super ionic conductivity, severe anisotropic thermal expansion coefficient, strong electromagnetic wave absorption, etc., have been discovered in HECs. As a response to the rapid development in this nascent field, this article gives a comprehensive review on the structure features, theoretical methods for stability and property prediction, processing routes, novel properties, and prospective applications of HECs. The challenges on processing, characterization, and property predictions are also emphasized. Finally, future directions for new material exploration, novel processing, fundamental understanding, in-depth characterization, and database assessments are given.

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The microstructure of the Sn-Ag-Cu solder is examined by optical microscopy and scanning electron microscopy (SEM) for various compositions near the ternary eutectic for different cooling rates from the solder melt. Focus is on the size and orientation of Sn grains as indicated by cross-polarized, light optical microscopy, and pole figures from x-ray diffraction. We find that both composition and cooling rate have strong influences on Sn grain size, with Sn grain size increasing an order of magnitude as Cu concentration increases from 0% to 1.1%. Cyclic growth twinning, with twinning angles near 60°, is observed in Sn-Ag-Cu alloys near the composition Sn-3.9Ag-0.6Cu.

Piezoelectric polymers with good flexibility have attracted tremendous attention in wearable sensors and energy harvesters. As the piezoelectricity of polymers such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride− trifluoroethylene [P(VDF−TrFE)] is lower than that of their ceramic counterparts, various approaches have been employed to improve the piezoelectric output of PVDF-based sensors, such as electrospinning, heat annealing, nanoconfinement, polymer blending, and nanoparticle addition. Here, we report two strategies to improve the piezoelectric sensing performance of polymer-based piezoelectric nanofibers, which include the formation of barium titanate (BTO)/P(VDF−TrFE) composite nanofibers and fabrication of penetrated electrodes to enlarge the interfacial area. BTO/P(VDF−TrFE) nanofibers with a BTO weight fraction of 5 wt % exhibit the maximum β-phase crystallinity and piezoelectricity. The piezoelectric output of the BTO/ P(VDF−TrFE) nanofiber mat is significantly improved compared with that of pristine P(VDF−TrFE), which is confirmed by piezoresponse force microscopy (PFM) and compression loading tests. In order to form the penetrated electrodes, oxygen (O 2 ) plasma treatment is employed, followed by an electroless plating process. The BTO/P(VDF−TrFE) nanofibers with penetrated electrodes demonstrate increased dielectric constants and enhanced piezoelectric outputs. A BTO/P(VDF−TrFE) nanofiberbased sensor with penetrated electrodes is capable of discerning the energy of a free-falling ball as low as 0.6 μJ and sensing the movement of a walking ant.

Grain-boundary deformation is the primary failure mode observed in solder joints. Understanding the effects of alloy composition variations and cooling rates on microstructural stability and deformation processes will allow development of improved joints. The effects of these variables on grain-boundary character were investigated in a pure-tin ingot and a reflowed sample; ingots of Sn-3.5wt.%Ag and Sn-3.8wt.%Ag-0.7wt.%Cu; and solder balls with 1.63-wt.% or 3-wt.% Ag. The microstructure was characterized using orientation imaging microscopy (OIM). After aging (150°C for 200 h), the fine-grained polycrystalline microstructure in both pure-tin specimens grew considerably, revealing preferred misorientations and ledge formation at grain boundaries. Aging of the alloy ingots showed only slight grain growth caused by precipitate pinning. The solder balls showed similar phenomena. The role of alloying elements, cooling rate, and the anisotropy of the coefficient of thermal expansion (CTE) in tin on microstructural evolution, grain-boundary character, and properties of solder joints are discussed.

Hydrodynamic models have been widely used in urban flood modelling. Due to the prohibitive computational cost, most of urban flood simulations have been currently carried out at low spatial resolution or in small localised domains, leading to unreliable predictions. With the recent advance in high-performance computing technologies, GPU-accelerated hydrodynamic models are now capable of performing high-resolution simulations at a city scale. This paper presents a multi-GPU hydrodynamic model applied to reproduce a flood event in a 267.4 km 2 urbanised domain in Fuzhou, Fujian Province, China. At 2 m resolution, the simulation is completed in nearly real time, demonstrating the efficiency and robustness of the model for high-resolution flood modelling. The model is used to further investigate the effects of varying spatial resolution and using localised domains on the simulation results. It is recommended that urban flood simulations should be performed at resolutions higher than 5 m and localised simulations may introduce unacceptable numerical errors.

A platinum network-based transparent electrode has been fabricated by electrospinning. The unique nanobelt structured electrode demonstrates low sheet resistance (about 16 Ω sq ) and high transparency of 80% and excellent flexibility. One of the most interesting demonstrations of this Pt nanobelt electrode is its excellent reversibly resilient characteristic. The electric conductivity of the flexible Pt electrode can recover to its initial value after 160% extending and this performance is repeatable and stable. The good linear relationship between the resistance and strain of the unique structured Pt electrode makes it possible to assemble a wearable high sensitive strain sensor. Present reported Pt nanobelt electrode also reveals potential applications in electrode for flexible fuel cells and highly transparent ultraviolet (UV) sensors.

The Yellow River and the Yangtze River contribute ~10% of the global fluvial sediment flux to the oceans. Proper characterization of the sediments of the two rivers is critical to the knowledge of their fate in the marginal seas of the west Pacific Ocean. Magnetic measurements have been made on bulk sediments as well as on separated particle size fractions of representative samples from the Yellow and Yangtze River estuaries, with the purpose of providing an efficient means of differentiating both groups of river sediments from each other. We found that on average the Yangtze River estuary sediments have relatively higher ferrimagnetic mineral contents and ferrimagnetic to antiferromagentic ratios compared with the Yellow River estuary sediments. A diagram of Saturated Isothermal Remanent Magnetization (SIRM) versus the demagnetization parameter S−100 can clearly distinguish sediments from the two rivers. Detailed magnetic measurements carried out on particle size fractions provide additional confirmation of magnetic contrasts between the two sets of river sediment samples. These contrasts reflect differences in lithology and weathering regimes in the catchments. To minimize possible biogenic and postdepositional diagenetic overprint in the marine environment, it is recommended that magnetic comparison on the coarser materials (eg, >4 µm) be carried out in addition to bulk measurements. This study shows that the magnetic approach can therefore provide a potentially efficient means of discriminating sediment sources in the Yellow Sea and East China Sea. In view of the rapid variations in sediment load carried by these two rivers in recent years, the present data set also provides a baseline against which possible future variations in sediment composition resulting from catchment changes can be assessed.