Microstructural Engineering Research Articles

Unraveling the Design Principles of Battery‐Supercapacitor Hybrid Devices: From Fundamental Mechanisms to Microstructure Engineering and Challenging Perspectives (Adv. Energy Mater. 26/2022)

Battery-Supercapacitor Hybrid Devices In article number 2200594, Zhong-Shuai Wu and co-workers overview the basic concept, working principles, and key scientific issues of battery-supercapacitor hybrid devices, summarize innovative approaches to the design and synthesis of advanced electrode materials, interface engineering, cell voltage expansion and some new-type battery-supercapacitor hybrid devices, and offer a perspective on the future of the field and the challenges that face it.

Precipitate number density determination in microalloyed steels by complementary atom probe tomography and matrix dissolution

Particle number densities are a crucial parameter in the microstructure engineering of microalloyed steels. We introduce a new method to determine nanoscale precipitate number densities of macroscopic samples that is based on the matrix dissolution technique (MDT) and combine it with atom probe tomography (APT). APT counts precipitates in microscopic samples of niobium and niobium-titanium microalloyed steels. The new method uses MDT combined with analytical ultracentrifugation (AUC) of extracted precipitates, inductively coupled plasma–optical emission spectrometry, and APT. We compare the precipitate number density ranges from APT of 137.81 to 193.56 × 1021 m−3 for the niobium steel and 104.90 to 129.62 × 1021 m−3 for the niobium-titanium steel to the values from MDT of 2.08 × 1021 m−3 and 2.48 × 1021 m−3. We find that systematic errors due to undesired particle loss during extraction and statistical uncertainties due to the small APT volumes explain the differences. The size ranges of precipitates that can be detected via APT and AUC are investigated by comparison of the obtained precipitate size distributions with transmission electron microscopy analyses of carbon extraction replicas. The methods provide overlapping resulting ranges. MDT probes very large numbers of small particles but is limited by errors due to particle etching, while APT can detect particles with diameters below 10 nm but is limited by small-number statistics. The combination of APT and MDT provides comprehensive data which allows for an improved understanding of the interrelation between thermo-mechanical controlled processing parameters, precipitate number densities, and resulting mechanical-technological material properties.Graphical abstract

Physically driven enhancement of the stability of Bi2O3-based ionic conductors via grain boundary engineering

Fast oxygen-ion conductors for use as electrolyte materials have been sought for energy conversion and storage. Bi2O3-based ionic conductors that exhibit the highest known oxygen-ion conductivities have received attention for use in next-generation solid electrolytes. However, at intermediate temperatures below ~600 °C, their conductivities degrade rapidly owing to a cubic-to-rhombohedral phase transformation. Here, we demonstrate that physical manipulation of the grain structure can be used to preserve the superior ionic conductivity of Bi2O3. To investigate the effects of microstructural control on stability, epitaxial and nanopolycrystalline model films of Er0.25Bi0.75O1.5 were fabricated by pulsed laser deposition. Interestingly, in situ impedance and ex situ XRD analyses showed that the grain boundary-free epitaxial film significantly improved the stability of the cubic phase, while severe degradation was observed in the conductivity of its polycrystalline counterpart. Consistently, the cation interdiffusion coefficient measured by the Boltzmann–Matano method was much lower for the epitaxial thin film compared to the polycrystalline thin film. Furthermore, first-principles calculations revealed that the presence of grain boundaries triggered the structural resemblance between cubic and rhombohedral phases, as evidenced by radial distribution functions. Additionally, phase transition energetics predicted that the thermodynamic stability of the cubic phase with respect to the rhombohedral counterpart is reduced near grain boundaries. Thus, these findings provide novel insights into the development of highly durable superionic conductors via microstructural engineering.

Thermoelectric performance of hydrothermally synthesized micro/nano Cu2-xS

Among the state-of-the-art thermoelectric materials, copper sulfides (Cu2S) have been predicted as promising thermoelectric materials due to their low intrinsic thermal conductivity. However, they still confront the problems with lower electrical properties, which distinctly restrict their thermoelectric application. Significant enhancement of thermoelectric properties is a great challenge owing to the common interdependence of electrical and thermal conductivity. Herein, a micro/nano Cu2-xS composite, with significantly enhanced thermoelectric properties, is prepared via a simple hydrothermal method. Due to the synergistic effect of the introduced nanostructure and the increased Cu1.96S contents, the micro/nano Cu2-xS bulk samples present a power factor of 10.1 μW cm−1 K−2 at 773 K. Meanwhile, a decrease of the thermal conductivity to 0.69 W m−1 K−1 is obtained, originating from the strong phonon scattering of micro/nano structure. Remarkably, a ZTmax value of 1.1 at 773 K is obtained, which is higher than the reported Cu2-xS thermoelectric material using chemical methods. This study proposes a facile microstructure engineering strategy for the development of high-performance thermoelectric materials.

Microstructural engineering of high-power redox flow battery electrodes via non-solvent induced phase separation

Redox flow batteries (RFBs) are emerging as viable options for grid-scale energy storage, but their elevated costs hamper commercialization. Enhancing the porous carbon electrode performance to improve power density and reduce system costs is an effective strategy toward widespread deployment; however, the porous carbon electrode must satisfy multiple contradictory roles, including providing high surface area, low pressure drop, and facile mass transport, thus motivating electrode engineering efforts. In this work, we systematically explore the non-solvent induced phase separation (NIPS) technique as a platform to synthesize a family of distinct microstructures for use in RFBs. Flow cell studies in commercially relevant redox pairs (i.e., Fe 2+/3+ , V 2+/3+ , and V 4+/5+ ) are performed, revealing diverse performance profiles, synthesis-structure-performance relationships, and opportunities for high-power electrode materials. We anticipate that, with further refinement and customization, NIPS electrodes can broadly benefit electrode engineering efforts for electrochemical energy storage and conversion applications. • Non-solvent induced phase separation as a versatile and facile synthetic platform • Porous electrodes with tunable microstructure • Synthesis-property-performance relationships for flow battery electrodes • High power density redox flow batteries Jacquemond et al. develop a versatile synthetic approach, based on non-solvent induced phase separation, to manufacture porous electrodes for redox flow batteries. Through a systematic study of synthetic conditions, the authors elucidate manufacturing-microstructure-performance relationships and demonstrate high power density operation in redox flow batteries using the novel electrodes.

Recent progress in the CoCrNi alloy system

The exceptional mechanical properties, particularly at cryogenic temperatures, of the equiatomic CoCrNi alloy are documented in numerous published studies. Similar to the equiatomic CoCrFeMnNi (so called Cantor alloy), from which the ternary alloy was derived, the CoCrNi ternary possesses low stacking fault energy that promotes complex deformation modes, as well as the activation of deformation twinning at ambient temperatures and increased strain. In addition to outstanding deformation mechanisms, chemical short-range order and face-centered cubic (FCC)-hexagonal close packed (HCP) transitions have been verified in this alloy and prove to be key factors contributing to the alloy's notable properties. The relationship between stacking fault energy and FCC→HCP phase transitions has been developed over the years through other low stacking fault materials, but the question that arises is: do well established physical metallurgical mechanisms require modification when applied to systems such as CoCrNi given their compositional complexity? Local chemical order plays an important role in that it brings the deviation from the random solid solution behavior generally expected from complex concentrated alloys. In this review, the fundamental atomistic deformation mechanisms of the CoCrNi alloy will be reviewed with a focus on deformation substructures and chemical short-range ordering. Recent studies on microstructural engineering through thermo-mechanical processing and efforts to enhance the tensile properties of the CoCrNi derived systems with minor alloying additions are discussed. Finally, future directions of research, which involve applying current understanding of the underlying mechanisms towards alloy design strategies, are discussed.

Microstructure Engineering of Hexagonal Boron Nitride for Single‐Photon Emitter Applications

AbstractSingle‐photon emitters (SPEs) can play an important role in future quantum optics. Hexagonal boron nitride (h‐BN), a layered insulator (bandgap ≈6 eV), is a promising candidate for next‐generation SPEs because of its chemical and thermal stability and high brightness at room temperature. In this review, the microstructures (atomic defects, deformations, and cavities) of h‐BN are established and their SPE characteristics are analyzed. Recent progress in the synthesis of high‐quality bulk h‐BN, monoisotopic h‐BN, and epitaxial h‐BN films is also demonstrated. Some approaches for achieving SPE arrays are further discussed and the applications of h‐BN SPEs in the quantum field are investigated. The success in the preparation of large‐scale h‐BN and its microstructural engineering provides a promising future in low‐dimensional quantum optics.

Heterogeneous Diamond-cBN Composites with Superb Toughness and Hardness.

The traditional hardness-toughness tradeoff poses a substantial challenge for the development of superhard materials. Due to strong covalent bonds and intrinsic brittleness, the full advantage of microstructure engineering for enhanced mechanical properties requires further exploration in superhard materials. Here heterogeneous diamond-cBN composites were synthesized from a carefully prepared precursor (hBN microflakes uniformly wrapped by onion carbon nanoparticles) through phase transitions under high pressure and high temperature. The synthesized composites inherit the architecture of the precursors: cBN regions with an anisotropic profile that spans several micrometers laterally and several hundred nanometers in thickness are embedded in a nanograined diamond matrix with high-density nanotwins. A significantly high fracture toughness of 16.9 ± 0.8 MPa m1/2 is achieved, far beyond those of single-crystal diamond and cBN, without sacrificing hardness. A detailed TEM analysis revealed multiple toughening mechanisms closely related to the microstructure. This work sheds light on microstructure engineering in superhard materials for excellent mechanical properties.

Unraveling the Design Principles of Battery‐Supercapacitor Hybrid Devices: From Fundamental Mechanisms to Microstructure Engineering and Challenging Perspectives

AbstractBattery‐supercapacitor hybrid devices (BSHDs) are aimed to be competitive complements to conventional batteries and supercapacitors by simultaneously achieving high energy density, high power density, and excellent cycling stability. However, the cooperative coupling of different energy storage mechanisms between batteries and supercapacitors is still challenging. Therefore, it is important to have a holistic understanding of BSHDs from material synthesis to final application. In this review, the basic concept and working principles of BSHDs are first discussed, which helps identify the related key scientific problems arising from hybridization. Then the ways in which some of these issues have been mitigated are discussed, for example by developing advanced microstructures and engineering the interface between electrode|current collector, electrode|electrolyte, and battery‐type(b‐type)|capacitor‐type(c‐type) materials. Furthermore, along with shedding light on innovative approaches for expanding the BSHDs’ cell voltage unconventional charge‐storage mechanisms and device configurations like dual ion and hydrogen ion hybrid supercapacitors are also summarized to push their performance even higher. Finally, a perspective on the technological challenges and future prospects of BSHDs from both an academic and industrial point of view is provided. This review is expected to serve as a window to look at the past and guide the future development of high‐performance BSHDs.

Surface microstructural engineering of continuous fibers as one-dimensional multifunctional fiber materials for wearable electronic applications

The rapid progress in advanced functional fibers (AFFs) offers unique superiorities in wearable electronics, artificial intelligence, and healthcare monitoring. However, there remain considerable challenges for AFFs to fulfill specific requirements of advanced applications due to their low electrical outputs, limitation in materials selection, and difficulty in regulating microstructures on narrow and curved surface of the fibers. In this study, fabricating and regulating honeycomb porous microstructures (HPMs) on one-dimensional nonplanar fiber surfaces were proposed and systematically studied for developing AFFs with customized functionalities. As a demonstration of application, multifunctional silver-plated nylon fibers surface-engineered with HPMs (SNF@HPMs) were developed with the assistance of the BF method and were further fabricated into SNF@HPMs-based triboelectric nanogenerator (SNF@HPMs-TENG). The SNF@HPMs-TENG showed considerable electrical performances with a power density of 390.8 mW/m2 and good long-term stability, which can power portable electronics as capacitors, calculator, watch, and light up 150 LEDs. Moreover, a self-powered wearable sensor based on SNF@HPMs was also developed for monitoring the bending, tactile, and frictional stimuli in a real-time manner. The comprehension of HPMs mechanism on nonplanar fiber surface and demonstrated capability of the SNF@HPMs-TENG provide insights and guidance in regulating microstructures of fiber materials for developing AFFs with customizable functionalities.

A novel approach combining grain boundary engineering and grain boundary serration to enhance high-temperature hot corrosion resistance in Alloy 617

In this work, a novel idea of combining two established microstructural engineering approaches viz., grain boundary engineering (GBE) and grain boundary serration (GBS) through optimization of thermomechanical and thermal processing in Alloy 617 is investigated and the superior resistance of GBE+GBS microstructure to the high-temperature hot corrosion is demonstrated. To achieve the GBE+GBS microstructure, the GBS treatment was introduced as a part of the GBE processing schedule (i.e., incomplete GBE+GBS) and following the GBE treatment (i.e., complete GBE+GBS). The extent of GBS is found to be similar in all the processed specimens. However, the extent of GBE is observed to be lower in the specimens undergoing incomplete GBE+GBS. This is due to the occurrence of recrystallization and consequent infrequent multiple twinning. On the other hand, a higher extent of GBE is achieved in the specimens subjected to complete GBE+GBS owing to the retention of the optimized GBE microstructure following the GBS treatment. The synergistic influence of GBE and GBS on the hot corrosion behavior is assessed by exposing the as-received (AR) as well as optimized grain boundary engineered and serrated (GBES) specimens to a salt mixture at 1273 K. The percolation depth after 24h and 48h exposure is significantly lower in the GBES specimen (∼55 µm and ∼115 µm, respectively) than the AR condition (∼305 µm and ∼630 µm, respectively). This is ascribed to the incorporation of Σ3n (n ≤3) and serrated boundaries in the GBES microstructure which obstructed the infiltration of harmful species into the alloy.

Crystal-facet and microstructure engineering in ZnO for photocatalytic NO oxidation

Photocatalysis is believed to be an important way of reducing NO pollutant in air and the facet engineering of semiconducting oxides could enhance the efficiency of the photocatalysis. ZnO nanoparticles with different exposed crystalline facets were successfully synthesized using a hydrothermal method and their photocatalytic degradation towards NO was investigated. The crystals from ZnCl2 precursor were hexagonal mesoporous ones with exposed (0002) facet, while those from zinc acetate were in the form of flakes or wheat ears with enhanced exposure of (101(−)1) facet. Calcination in air imparted an enhanced the textural coefficient of the orientated facets as well as the oxygen defects. The nanocrystals with enhanced (0002) facet and lower flat-band energy did better in photoelectrochemical water-oxidation than those with exposed (101(−)1) facet that showed superior photocatalytic activity (approaching 76.7 ± 0.6% under 365 nm photons) for NO oxidation. According to theoretical calculations, (101(−)1) facet with O termination showed much higher affinity to NO molecules than other configurations, and the oxygen vacancy in ZnO played an minor role in the photocatalytic oxidation of NO. A high quantum efficiency approaching 97.5 ± 1.4% under 275 nm photons was obtained for the ZnO crystals from zinc acetate with mixed (0002) and (101(−)1) facets. This research explores the special characteristics of ZnO with different exposed facets and is important for the future design of highly efficient photocatalyst for hazardous material removal.

Directional combustion induced by 3D aligned carbon channel arrays for combustion chamber-free micro-thruster

Micro-solid propellant thrusters are widely used in propulsion and attitude adjustment of micro-spacecraft, and nano-satellites prospect. However, they suffer from low specific impulse owing to the existence of the conventional structural parts (combustion chamber and nozzle) that account for a large weight ratio. Herein, we report a combustion chamber-free micro-thruster consisting of balsa wood-derived carbon aerogel as well as ammonium perchlorate (AP) and Ti3C2 MXene supported on carbon aerogel. The microstructure engineering design of carbon aerogel give it 3D aligned channel arrays structure and defect rich carbon framework. The 3D aligned channel could guide the burning fluid in the channel to form directional flame, thus converting heat energy into kinetic energy with absence of the additional combustion chamber and nozzle. The defect-rich carbon aerogel with high reactivity could participate in the combustion reaction as fuel. To further promote the combustion performance of the chamber-free micro-thruster, Ti3C2 MXene is applied as reactive combustion catalyst to accelerate the thermal decomposition of AP. Coupled with the advantageous of chamber-free, high combustion efficiency, and efficient heat and mass transfer in the channel structure, the Ti/CA/AP composite can be directly applied as a micro-thruster and generates a high specific impulse of 2044.0 N·s/kg.

Microstructural engineering of medium entropy NiCo(CrAl) alloy for enhanced room and high-temperature mechanical properties

This work demonstrates the development of a strong and ductile medium entropy alloy by employing conventional alloying and thermomechanical processing to induce partial recrystallization (PR) and precipitation strengthening in the microstructure. First, the cold working of homogenized alloy resulted in a highly deformed microstructure. On annealing at 700 °C, B2 ordered precipitates heterogeneously nucleate on the highly misoriented sites. These B2 promotes particle stimulated nucleation (PSN) of new recrystallized strain-free grains. The migration of recrystallized grain boundaries leads to discontinuous precipitation of L12 ordered regions in highly dense lamellae structures. We also observe near-spherical L12 precipitates in the non-recrystallized grains. Atomic-scale compositional analysis reveals a significant amount of Ni confined to the Phase Boundary (PB) regions between B2 and L12 precipitates, indicating Ni as a rate-controlling element for coarsening the microstructure. On 20 h of annealing, the alloy comprises a composite microstructure of recrystallized and non-recrystallized grains, B2 particles at the grain boundaries (GBs), and coherent L12 precipitates inside the grains. The microstructure results in a 0.2% yield stress (YS) value of ∼1060 MPa with ∼25% elongation at ambient temperature and retains up to ∼910 MPa at 670 °C. Examination of deformed microstructure reveals excessive twinning, formation of stacking faults, shearing of L12 precipitates, and accumulation of dislocations at around the B2 precipitates and GBs attributed to high strain hardening of the alloy.

Electrode-to-electrode monolithic integration for high-voltage bipolar solid-state batteries based on plastic-crystal polymer electrolyte

• The EtE monolithic integration process is proposed for high-voltage bipolar SSBs. • Plastic-crystal polymer electrolyte (PCPE) was infused into a porous electrode. • The infused PCPE enables the fast Li + conduction and intimate interfacial contact. • The microstructural engineering results in enhanced performance of SSB. • The efficacy of the EtE-integration procedure is demonstrated in a bipolar SSB. Solid-state batteries (SSBs) offer a fundamental solution to mitigate the safety and reliability issues of conventional lithium-ion batteries utilizing flammable liquid electrolytes, and enable the bipolar configuration of high-voltage and high-energy storage systems. However, the conventional layer-by-layer (LbL) stacking process using individual electrolyte and electrode layers suffers from poor electrolyte–electrode contacts and challenging process complications for manufacturing multi-layer bipolar SSBs. Herein, we report an electrode-to-electrode (EtE) monolithic integration without a free-standing solid electrolyte layer for high-voltage bipolar SSBs. Positive and negative electrodes seamlessly combined with a thin solid electrolyte are fabricated by the infusion of a plastic-crystal-based polymer electrolyte (PCPE) into porous electrodes with a subsequent ultraviolet-induced solidification process. The infused PCPE in the electrodes forms continuous Li + conduction channels as well as intimate solid–solid interfaces. The thin PCPE film (∼10 μm) formed in situ on the top of the electrodes during the infusion process provides ultra-high Li + conductance (∼3.1 S cm −2 at 45 °C) between the two electrodes. SSBs are constructed via direct integration of the PCPE-infused electrodes: a unit cell-type SSB with LiNi 0.6 Co 0.2 Mn 0.2 O 2 (positive) and Li 4 Ti 5 O 12 (negative) show superior capacity (∼160 mAh g −1 ), rate capability (98 mAh g −1 at 2C), and stable cyclability (81% after 100 cycles) at 45 °C than the SSB fabricated by the conventional LbL stacking process. Moreover, a 10 V-class, bipolar SSB comprising five unit cells stacked in series is constructed via the EtE monolithic integration of multiple PCPE-infused bipolar electrodes, and its stable cycle performance is corroborated with a capacity retention of 84%. This work demonstrates that the suggested EtE integration process offers a promising strategy to addressing the interfacial contact issues of SSBs, thereby being utilized to realize scalable, low-cost, high-voltage bipolar SSBs.

Improved elastocaloric effect of NiTi shape memory alloys via microstructure engineering: A phase field simulation

By newly introducing a grain boundary energy, a grain size (GS) dependent and thermo-mechanically coupled phase field model was proposed to investigate the elastocaloric effect (eCE) of NiTi shape memory alloys (SMAs), and discuss the effects of GS, texture, gradient-nanograin and bimodal grain structures as well as geometric gradient on the eCE through simulations. The simulated results show that with decreasing the GS, the gradual reduction of the degree of martensite transformation (MT) and the variation of transformation mode in the nano-polycrystalline NiTi SMA system lead to the decreasing absorption of transformation latent heat, and the gradual weakness and even disappearance of local instability during MT decreases the hysteresis, resulting in the increase of the coefficient of performance (COPmat); the deformation dependence of COPmat and the grain orientation dependence of transformation instability lead to a dependence of COPmat on texture, which can be enhanced with decreasing the GS. It is further found that the microstructure engineering (from the perspectives of GS, texture, gradient-nanograin and bimodal grain structures) can significantly improve the COPmat, and the introduction of geometric gradient can effectively reduce the MT start stress. Several microstructure and geometric schemes with considerable adiabatic temperature change (ΔTad) and high COPmat as well as relatively low MT start stress are reported, which can provide an important theoretical guidance for improving the eCE of NiTi SMAs and exploiting excellent SMA-based elastocaloric materials. The proposed phase field model and the characterization method for texture can be used as a reference to simulate the eCE and anisotropic MT of other SMAs.

From Synthesis to Microstructure: Engineering the High-entropy Ceramic Materials of the Future

Sintering and microstructural development in ceramics has long been studied in a two-dimensional grain size-density space, with only texture (i.e. deviation of grain orientation from random) used to gain first insights into additional parametric spaces. Following an increased interest for grain boundary engineering and a deeper understanding of dopant effects on sintering and grain boundaries, the theory of complexion transitions for ceramics has been introduced over the last decade, providing a new base for advanced microstructure engineering in ceramics. With emergence of high entropy ceramics over the last 5 years, the combination of both yields new grounds for exploration and engineering of functional ceramic materials of the future.

Ultrahigh Piezoelectric Performance through Synergistic Compositional and Microstructural Engineering.

Piezoelectric materials enable the conversion of mechanical energy into electrical energy and vice‐versa. Ultrahigh piezoelectricity has been only observed in single crystals. Realization of piezoelectric ceramics with longitudinal piezoelectric constant (d 33) close to 2000 pC N–1, which combines single crystal‐like high properties and ceramic‐like cost effectiveness, large‐scale manufacturing, and machinability will be a milestone in advancement of piezoelectric ceramic materials. Here, guided by phenomenological models and phase‐field simulations that provide conditions for flattening the energy landscape of polarization, a synergistic design strategy is demonstrated that exploits compositionally driven local structural heterogeneity and microstructural grain orientation/texturing to provide record piezoelectricity in ceramics. This strategy is demonstrated on [001]PC‐textured and Eu3+‐doped Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PMN‐PT) ceramics that exhibit the highest piezoelectric coefficient (small‐signal d 33 of up to 1950 pC N–1 and large‐signal d 33* of ≈2100 pm V–1) among all the reported piezoelectric ceramics. Extensive characterization conducted using high‐resolution microscopy and diffraction techniques in conjunction with the computational models reveals the underlying mechanisms governing the piezoelectric performance. Further, the impact of losses on the electromechanical coupling is identified, which plays major role in suppressing the percentage of piezoelectricity enhancement, and the fundamental understanding of loss in this study sheds light on further enhancement of piezoelectricity. These results on cost‐effective and record performance piezoelectric ceramics will launch a new generation of piezoelectric applications.

Upgrading of superior strength–ductility trade-off of CoCrFeNiMn high-entropy alloy by microstructural engineering

One of the challenging phenomena in the materials science community is the issue of the strength-ductility trade-off. Pre-strain followed by annealing at low temperatures was used as a novel strategy to overcome the strength-ductility trade-off of CoCrFeNiMn high entropy alloy. The proposed process aims to retain the deformation-induced twins after partial recovery. However, the lack of precipitate in the processed alloy bears in mind to consider the effect of precipitation. In this paper, for the first time, we proposed a simple thermomechanical process including light cryogenic rolling (reduction of thickness ∼28%) followed by low-temperature annealing (at 500 °C for 180 min) to obtain a unique microstructure. The microstructure with partial recovery contains retained deformation-induced twins along with bcc Cr-rich precipitates under optimum conditions (size and volume fraction) and no brittle sigma precipitates. This microstructure provides the appropriate balance between deformation and precipitation strengthening. The microstructure exhibits much improved mechanical properties (UTS ∼1.25 GPa and uniform elongation ∼15%). Additionally, a model was introduced for predicting mechanical properties using microstructural parameters. The present results indicated that this thermomechanical processing could be used as an innovative processing strategy for achieving superior strength–ductility trade-off by microstructural engineering. We believe that a similar concept may be applied for optimizing the mechanical properties of other fcc high or medium entropy alloys based on the Co-Cr-Fe-Ni-Mn system.

Engineering the Defects and Microstructures in Ferroelectrics for Enhanced/Novel Properties: An Emerging Way to Cope with Energy Crisis and Environmental Pollution.

In the past century, ferroelectrics are well known in electroceramics and microelectronics for their unique ferroelectric, piezoelectric, pyroelectric, and photovoltaic effects. Nowadays, the advances in understanding and tuning of these properties have greatly promoted a broader application potential especially in energy and environmental fields, by harvesting solar, mechanical, and heat energies. For example, high piezoelectricity and high pyroelectricity can be designed by defect or microstructure engineering for piezo‐ and pyro‐catalyst, respectively. Moreover, highly piezoelectric and broadband (UV–Vis–NIR) light‐responsive ferroelectrics can be designed via defect engineering, giving rise to a new concept of photoferroelectrics for efficient photocatalysis, piezocatalysis, pyrocatalysis, and related cocatalysis. This article first summarizes the recent developments in ferroelectrics in terms of piezoelectricity, pyroelectricity, and photovoltaic effects based on defect and microstructure engineering. Then, the potential applications in energy generation (i.e., photovoltaic effect, H2 generation, and self‐powered multisource energy harvesting and signal sensing) and environmental protection (i.e., photo‐piezo‐pyro‐ cocatalytic dye degradation and CO2 reduction) are reviewed. Finally, the outlook and challenges are discussed. This article not only covers an overview of the state‐of‐art advances of ferroelectrics, but also prospects their applications in coping with energy crisis and environmental pollution.