Micro- structures - Academia.edu (original) (raw)

Papers by Micro- structures

Microstructures, 2023

Chromium (Cr) plays a critical role in the corrosion resistance of conventional alloys via the fo... more Chromium (Cr) plays a critical role in the corrosion resistance of conventional alloys via the formation of a dense Cr oxide-based passive film. However, the exact role of Cr in the corrosion of high-entropy alloys (HEAs) remains unclear. The effect of Cr content on the corrosion behavior of the ultrafine-grained Cr x MnFeCoNi (x = 0, 0.6, 1, and 1.5) HEAs in the sulfuric acid solution (0.5 M H 2 SO 4) was investigated. These HEAs were fabricated using a combination of mechanical alloying and spark plasma sintering. The electrochemical tests show that the passive film was more compact and thicker at higher Cr concentration, but the corrosion rate first increased and then decreased, due to the presence of the nanocrystalline-amorphous phase boundaries in the passive film. Long-time immersion tests show that the corrosion rate increased exponentially with the Cr content, due to the gradual accumulation of the galvanic corrosion.

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Microstructures, 2023

The need for specialty powder composition limits the processing of a wide range of alloy products... more The need for specialty powder composition limits the processing of a wide range of alloy products via the laser powder bed fusion (LPBF) technique. This work extends the adaptability of the LPBF technique by fabricating the first-ever Fe-30Mn-6Si (wt.%) product for potential use as a biodegradable shape memory alloy (SMA). Different LPBF processing parameters were assessed by varying the laser power, scan speed, and the laser re-scan strategy to achieve a fully dense part. The microstructure was found to respond to the processing conditions. For example, the microstructure of the parts produced by the high linear energy density (LED) had a columnar and strong crystallographic texture, while in the low LED, the parts were almost equiaxed and had a weak texture. To explain the evolved microstructure, the thermal history of the LPBF products was computed using the finite element analysis (FEA) of the melt pool gathered from a single-track laser scan experiment. The FEA results showed a varying temperature gradient, cooling and solidification rates, and temperature profile as a function of LED. Then, the relationship of hardness between grain size, phases present, and crystallographic misorientation of the LPBFbuilt alloy was analysed with reference to a control alloy of similar composition but prepared by arc melting. This study validates the LPBF processability of Fe-Mn-Si SMA and provides a new insight into the influence of processing parameters on the formed microstructure and hardness.

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Microstructures, 2023

Supercapacitors (SCs) have drawn growing attention due to their advantages in fast charge/dischar... more Supercapacitors (SCs) have drawn growing attention due to their advantages in fast charge/discharge over batteries. Benefiting from their prominent electrical conductivity and metal-like characteristics, transition metal nitrides have emerged as promising electrode materials for SCs. Traditional ways to prepare metal nitrides through ammonolysis are inconvenient and induce severe environmental pollution. Herein, we report a facile synthetic method toward heterogenous Ni 3 N-Co 2 N 0.67 /nitrogen-doped carbon (Ni 3 N-Co 2 N 0.67 /NC) hollow nanoflower via pyrolyzing NiCo-TEOA (triethanolamine) complex precursor applying urea as nitrogen source. Electrochemical tests demonstrate that the Ni 3 N-Co 2 N 0.67 /NC nanoflower delivers good specific capacitance (1582 F g-1 at 1 A g-1) and steady cycle performance (83.79% after 5000 cycles). Moreover, the as-assembled Ni 3 N-Co 2 N 0.67 /NC//AC cell can reach a peak energy density of 32.4 W h kg-1 at a power density of 851.3 W kg-1. The excellent electrochemical performance confirms extensive application prospects of the Ni 3 N-Co 2 N 0.67 /NC nanoflower.

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Microstructures, 2023

NaNbO 3-based lead-free energy storage ceramics are essential candidates for next-generation puls... more NaNbO 3-based lead-free energy storage ceramics are essential candidates for next-generation pulsed power capacitors, especially under the background of energy saving and environmental protection. However, the roomtemperature antiferroelectric P phase of pure NaNbO 3 ceramics limits its further development in energy storage owing to the irreversible antiferroelectric to ferroelectric phase transition under electric fields. In this work, CaZrO 3 was introduced to NaNbO 3 ceramics to destroy the long-range polarization ordering but keep large antiferrodistortion, causing the formation of superparaelectric state with macrodomains, which can be identified by the refinement results of high-energy synchrotron X-ray diffraction, neutron diffraction and TEM results. Combined with the fine grains, dense and homogeneous microstructure, ergodic relaxation behaviors, and delayed polarization saturation, a high recoverable energy storage density of ~5.4 J/cm 3 and efficiency of ~82% can be realized in 0.85NaNbO 3-0.15CaZrO 3 ceramics at an ultrahigh breakdown electric field of ~68 kV/mm. The results found in this work suggest that the supersparaelectric with non-cubic phase would be a good candidate for generating excellent dielectric energy storage properties.

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Microstructures, 2023

The development of dielectric capacitors with high energy density and energy efficiency is of gre... more The development of dielectric capacitors with high energy density and energy efficiency is of great significance in the modern electronic components market. To reduce the high energy loss of Bi0.5Na0.5TiO3, 0.55Bi0.5Na0.5TiO3-0.45(Sr0.7Bi0.2)TiO3 (BNT-BST) nanofibers with a high aspect ratio are synthesized via electrospinning. To achieve a high energy density, the design of a symmetric trilayer nanocomposite consisting of a BNT-BST/polyvinylidene difluoride (PVDF) layer with a high dielectric constant sandwiched between two layers of pure PVDF is herein described. The trilayer structure can effectively alleviate the electric field concentration effect, resulting in a considerably enhanced breakdown strength and improved discharge energy density. The maximum discharge energy density of 17.37 J/cm3 at 580 kV/mm could be achieved in the symmetric trilayer nanocomposite with a BNT-BST/PVDF middle layer, which is 90.5% greater than that achieved using pure PVDF (9.21 J/cm3 at 450 kV/mm). This study presents a new case for developing dielectric capacitors with high energy density.

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Microstructures, 2023

Antiferroelectrics are a kind of unique dielectric materials, mainly due to their polarization be... more Antiferroelectrics are a kind of unique dielectric materials, mainly due to their polarization behavior, and composition-induced antiferroelectricity stability also draws considerable attention. In this work, single orthorhombic phase (Pb0.95Bi0.05)ZrO3 (PBZ), Pb(Zr0.95Bi0.05)O3 (PZB), and PbZrO3 (PZO) films with good density and flatten surface was prepared on Pt/Ti/SiO2/Si substrate via sol-gel method. Compared with pure PZO films, the PBZ and PZB films possess increased switching electric field difference Δ E due to enhanced forward switching field and the late response of backward switching field. In terms of stabilizing AFE phase, changing the tolerance factor t has the similar effect as Bi-doping the A/B sites in PZO, with the modification of the A-site being more effective than that of the B-site. PBZ films achieve a high recoverable energy density (Wrec) of 26.4 J/cm3 with energy efficiency (η) of 56.2% under an electric field of 1278 kV/cm, which exceeds other pure AFE materials. This work provides a fundamental understanding of the crystal structure-related antiferroelectricity of PZO materials and broadens the chemical doping route to enhance the electric properties of AFE materials.

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Microstructures, 2023

High entropy alloys (HEAs), as a new class of structural materials, have attracted extensive inte... more High entropy alloys (HEAs), as a new class of structural materials, have attracted extensive interest from numerous metallurgical scientists and engineers. Benefiting from their unique microstructural features and outstanding mechanical performance, HEAs have shown significant potential for applications in many engineering fields, even under extreme conditions. In particular, when exposed to hydrogen and/or intermediate-temperature environments, these HEAs inevitably suffer from severe environmental embrittlement (EE) issues, e.g., hydrogen embrittlement (HE) and intermediate-temperature embrittlement (ITE), resulting in serious premature intergranular failure. In this work, we critically review the state-of-the-art advances of EE in previously reported HEA systems. Particular focus is given to novel strategies to enhance the resistance to EE in different HEAs. Two critical embrittlement phenomena, namely, HE and ITE, are highlighted separately. Finally, we provide perspectives on future research directions and opportunities for EE-resistant HEAs.

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Microstructures, 2023

Broadband photodetectors covering the ultraviolet (UV) to visible range are significant for appli... more Broadband photodetectors covering the ultraviolet (UV) to visible range are significant for applications in communication and imaging. Broadband photodetectors with the capacity to distinguish wavelength bands are highly desirable because they can provide additional spectral information. Herein, we report a UV-visible distinguishable broadband photodetector based on a graphene/ZnO quantum dot heterostructure. The photodetector exhibits negative photoconductance under visible illumination because the adsorbents on graphene act as scattering centers to reduce the carrier mobility. In contrast, under UV illumination, the photodetector shows positive photoconductance as the photogenerated electrons in the ZnO quantum dots transfer to the graphene, thereby increasing the conductivity. Thus, the detection and distinction of UV and visible illumination can be realized by utilizing the opposing photoconductivity changes. These results offer inspiration for the design of multifunctional broadband photodetectors.

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Microstructures, 2022

Ultrafine-grained (UFG) metallic materials processed by severe plastic deformation (SPD) techniqu... more Ultrafine-grained (UFG) metallic materials processed by severe plastic deformation (SPD) techniques often exhibit significantly higher strengths than those calculated by the well-known Hall-Petch equation. These higher strengths result from the fact that SPD processing not only forms the UFG structure but also leads to the formation of other nanostructural features, including dislocation substructures, nanotwins and nanosized second-phase precipitations, which further contribute to the hardening. Moreover, the analysis of strengthening mechanisms in recent studies demonstrates an important contribution to the hardening due to phenomena related to the structure of grain boundaries as a non-equilibrium state and the presence of grain boundary segregations. Herein, the principles of the nanostructural design of metallic materials for superior strength using SPD processing are discussed.

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Microstructures, 2022

Commentary to publications by Prof. Jun Chen, University of Science and Technology Beijing, E-mai... more Commentary to publications by Prof. Jun Chen, University of Science and Technology Beijing, E-mail: junchen@ustb.edu.cn (10.1038/s41467-022-30821-7; 10.1016/j.actamat.2022.118115).

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Microstructures, 2022

Dielectric capacitors with ultrafast charge-discharge rates are extensively used in electrical an... more Dielectric capacitors with ultrafast charge-discharge rates are extensively used in electrical and electronic systems. To meet the growing demand for energy storage applications, researchers have devoted significant attention to dielectric ceramics with excellent energy storage properties. As a result, the awareness of the importance of the pulsed discharge behavior of dielectric ceramics and conducting characterization studies has been raised. However, the temperature stability of pulsed discharge behavior, which is significant for pulsed power applications, is still not given the necessary consideration. Here, we systematically investigate the microstructures, energy storage properties and discharge behaviors of nanograined (1-x)BaTiO3-xNaNbO3 ceramics prepared by a two-step sintering method. The 0.60BaTiO3-0.40NaNbO3 ceramics with relaxor ferroelectric characteristics possess an optimal discharge energy density of 3.07 J cm-3, a high energy efficiency of 92.6%, an ultrafast discharge rate of 39 ns and a high power density of 100 MW cm-3. In addition to stable energy storage properties in terms of frequency, fatigue and temperature, the 0.60BaTiO3-0.40NaNbO3 ceramics exhibit temperature-stable power density, thereby illustrating their significant potential for power electronics and pulsed power applications.

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Microstructures, 2022

Utilizing clean energy derived from photoelectrocatalytic reactions is expected to be an excellen... more Utilizing clean energy derived from photoelectrocatalytic reactions is expected to be an excellent choice to fundamentally solve the problem of the human energy crisis. Photoelectrochemical (PEC) cell can effectively promote charge separation and improve solar energy conversion efficiency since it combines the advantages of photocatalysis and electrocatalysis. However, the hole transfer and subsequent oxidation reaction in the PEC process are slow, resulting in the rapid recombination of photogenerated electron-hole pairs and low PEC performance. The half-oxidation reaction involving photogenerated holes is the bottleneck of PEC water splitting. Therefore, hole modulation has been an important research area in the field of catalysis. However, compared with electron modulation, research on hole modulation is limited and still faces great challenges. It is therefore of great significance to develop effective modulation strategies for photogenerated holes. This review summarizes the hole modulation strategies developed in the last five years, including hole sacrificial agents, nanostructural modification, heterostructure construction and cocatalyst modification. Hole modulation dynamics studies, such as transient absorption spectroscopy, time-resolved photoluminescence spectroscopy, transient photovoltage and scanning electrochemical microscopy, are also summarized. Moreover, relevant conclusions and an outlook are proposed.

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Microstructures, 2022

Understanding the dynamic behavior of domain structures is critical to the design and application... more Understanding the dynamic behavior of domain structures is critical to the design and application of super-elastic freestanding ferroelectric thin films. Phase-field simulations represent a powerful tool for observing, exploring and revealing the domain-switching behavior and phase transitions in ferroelectric materials at the mesoscopic scale. This review summarizes the recent theoretical progress regarding phase-field methods in freestanding ferroelectric thin films and novel buckling-induced wrinkled and helical structures. Furthermore, the strong coupling relationship between strain and ferroelectric polarization in super-elastic ferroelectric nanostructures is confirmed and discussed, resulting in new design strategies for the strain engineering of freestanding ferroelectric thin film systems. Finally, to further promote the innovative development and application of freestanding ferroelectric thin film systems, this review provides a summary and outlook on the theoretical modeling of freestanding ferroelectric thin films.

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Microstructures, 2022

Although near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are desired for non... more Although near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are desired for non-visible light source applications, the design of broadband NIR phosphors remains a challenge. Inspired by the chemical unit co-substitution strategy for the modification of composition and local structure, we realize a tunable redshift emission from 706 to 765 nm in garnet-type Lu3Sc2Ga3O12:Cr3+ with a broadened full width at half maximum and enhanced photoluminescence intensity by introducing a [Mg2+-Si4+] unit into the [Sc3+-Ga3+] couple. Structural and spectral analyzes demonstrate that the co-substitution reduces the local symmetry and crystal field strength of the [CrO6] octahedra, thus leading to inhomogeneous widening of the 4T2→4A2 emission and enhanced blue absorption. Furthermore, the 4T2→4A2 emission exhibits a phonon-assisted character at low temperatures due to the thermal coupling effect with the 2E level. The fabricated NIR pc-LED based on the optimized NIR phosphor exhibits excellent potential in night vision and imaging applications.

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Microstructures, 2022

β-solidifying TiAl alloys are considered as promising candidate materials for high-temperature st... more β-solidifying TiAl alloys are considered as promising candidate materials for high-temperature structural applications. Laser-based additive manufacturing (LAM) enables the fabrication of components with geometrical complexity in near-net shape, leading to time and feedstock savings. In this study, a gas-atomized Ti-44Al-4Nb-1Mo-1Cr powder is used as a feedstock material for LAM. However, the LAM of TiAl alloys remains a challenge due to serious cracking during the printing process. To minimize the cracking, the optimization of the LAM processing parameters is essential. Hence, the effects of the LAM processing parameters on the cracking susceptibility and microstructure are studied here. Our experimental results show that the cracking susceptibility can be mitigated by increasing the laser power. Accordingly, the microstructure transforms from the dominating α2 grains to a near-lamellar microstructure with an increment in laser power, leading to a reduction in microhardness, even though it is still higher than that of its as-cast counterparts. It is concluded that changes in the laser power can directly tailor the microstructure, phase composition and microhardness of LAM-fabricated TiAl alloys.

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Microstructures, 2022

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Microstructures, 2022

Materials with tunable negative thermal expansion (NTE) are highly demanded in various functional... more Materials with tunable negative thermal expansion (NTE) are highly demanded in various functional devices. La(Fe, Si)13-based compounds are promising NTE materials due to their outstanding NTE properties. However, their poor mechanical properties and related short service life restrict their practical applications. In this work, epoxy resin with positive thermal expansion is used to synthesize La-Fe-Si/resin composites. The NTE of La-Fe-Si/resin composites can be manipulated by optimizing the La-Fe-Si particle size and resin content, and tailoring resin content could tune the NTE more effectively. The average linear coefficient of thermal expansion of the composites decreases from -275.0 × 10-6 K-1 to -4.9 × 10-6 K-1 over the magnetic transition temperature range as the resin content increases from 3 wt.% to 80 wt.%. In addition, zero thermal expansion is achieved in the La-Fe-Si/resin composite with 20 wt.% resin. The resin would reinforce the binding force by filling the pores between the particles. The La-Fe-Si/resin composite with 80 wt.% resin exhibits highly improved mechanical properties; for example, its compressive strength of 205 MPa is 75% higher than that of the La-Fe-Si/resin composite with 3 wt.% resin. The prepared La-Fe-Si/resin composites can be machined into different shapes for practical applications, such as thin plates, strips, and rods. Furthermore, the La-Fe-Si/resin composites can undergo 1000 thermal cycles without NTE performance degradation and mechanical integrity loss, indicating durable cycle stability. Hence, significantly tunable NTE with high mechanical properties and long-term cycle stability makes La-Fe-Si/resin composites present great application potential as NTE materials.

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Microstructures, 2022

Extensive experiments have shown that the transformation from the face-centered cubic to hexagona... more Extensive experiments have shown that the transformation from the face-centered cubic to hexagonal close-packed ε phase usually occurs around coherent Σ3 boundaries. However, in this letter, we reveal a different transformation mechanism in a metastable dual-phase compositionally complex alloy via a systematic high-resolution scanning transmission electron microscopy analysis. The face-centered cubic γ matrix can be transformed to the hexagonal close-packed ɛ phase (as small as one unit) around an incoherent Σ3 boundary (~30 nm), i.e., the facet of the coherent Σ3 boundary. This transformation is assisted by the detwinning/twin growth of a coherent Σ3 boundary during annealing treatment (900 °C for 60 min).

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Microstructures, 2022

Lithium-ion batteries have made significant commercial and academic progress in recent decades. Z... more Lithium-ion batteries have made significant commercial and academic progress in recent decades. Zinc oxide (ZnO) has been widely studied as a lithium-ion battery anode due to its high theoretical capacity of 987 mAh g-1, natural abundance, low cost, and environmental friendliness. However, ZnO suffers from poor electronic conductivity and large volume variation during the battery discharge/charge process, leading to capacity deterioration during long-term cycling. Herein, porous ZnO@C nanoplates are developed to offer short ion diffusion pathways and good conduction networks for both Li ions and electrons. The porous nanoplates provide abundant active sites for electrochemical reactions with minimized charge transfer impedance. As a result, the porous ZnO@C nanoplates deliver higher performance for lithium-ion storage compared with a bare ZnO anode. Furthermore, with the introduction of reduced graphene oxide (rGO), the ZnO@C@rGO composite anode achieves a capacity of 229.3 mAh g-1 at a high current density of 2 A g-1.

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Microstructures, 2022

The effects of cold rolling and subsequent annealing on the microstructures and mechanical proper... more The effects of cold rolling and subsequent annealing on the microstructures and mechanical properties of Fe40Mn20Cr20Ni20 high-entropy alloys (HEAs) are investigated. The Cr-rich secondary phases with a tetragonal structure (σ phases) in the Fe40Mn20Cr20Ni20 HEAs are precipitated upon annealing at 600 °C-900 °C for 2 h. The prepared Fe40Mn20Cr20Ni20 HEA annealed at 800 °C for 2 h after cold rolling has a good combination of strength and elongation, with a high yield strength of 438 MPa, a high ultimate tensile strength of 676 MPa, and an excellent elongation to fracture of 32%. The mechanical properties at cryogenic temperature are better than those at room temperature. Typically, for the incompletely recrystallized alloy annealed at 700 °C, the yield strength, tensile strength, and elongation after fracture are increased by 26%, 22%, and 100%, respectively. This trend mainly depends on dislocation and twinning strengthening. The σ phases also improve the cryogenic tensile properties. Furthermore, the recrystallization kinetics of the Fe40Mn20Cr20Ni20 HEAs are explored to correlate with the deformation behavior.

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Microstructures, 2023

Chromium (Cr) plays a critical role in the corrosion resistance of conventional alloys via the fo... more Chromium (Cr) plays a critical role in the corrosion resistance of conventional alloys via the formation of a dense Cr oxide-based passive film. However, the exact role of Cr in the corrosion of high-entropy alloys (HEAs) remains unclear. The effect of Cr content on the corrosion behavior of the ultrafine-grained Cr x MnFeCoNi (x = 0, 0.6, 1, and 1.5) HEAs in the sulfuric acid solution (0.5 M H 2 SO 4) was investigated. These HEAs were fabricated using a combination of mechanical alloying and spark plasma sintering. The electrochemical tests show that the passive film was more compact and thicker at higher Cr concentration, but the corrosion rate first increased and then decreased, due to the presence of the nanocrystalline-amorphous phase boundaries in the passive film. Long-time immersion tests show that the corrosion rate increased exponentially with the Cr content, due to the gradual accumulation of the galvanic corrosion.

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Microstructures, 2023

The need for specialty powder composition limits the processing of a wide range of alloy products... more The need for specialty powder composition limits the processing of a wide range of alloy products via the laser powder bed fusion (LPBF) technique. This work extends the adaptability of the LPBF technique by fabricating the first-ever Fe-30Mn-6Si (wt.%) product for potential use as a biodegradable shape memory alloy (SMA). Different LPBF processing parameters were assessed by varying the laser power, scan speed, and the laser re-scan strategy to achieve a fully dense part. The microstructure was found to respond to the processing conditions. For example, the microstructure of the parts produced by the high linear energy density (LED) had a columnar and strong crystallographic texture, while in the low LED, the parts were almost equiaxed and had a weak texture. To explain the evolved microstructure, the thermal history of the LPBF products was computed using the finite element analysis (FEA) of the melt pool gathered from a single-track laser scan experiment. The FEA results showed a varying temperature gradient, cooling and solidification rates, and temperature profile as a function of LED. Then, the relationship of hardness between grain size, phases present, and crystallographic misorientation of the LPBFbuilt alloy was analysed with reference to a control alloy of similar composition but prepared by arc melting. This study validates the LPBF processability of Fe-Mn-Si SMA and provides a new insight into the influence of processing parameters on the formed microstructure and hardness.

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Microstructures, 2023

Supercapacitors (SCs) have drawn growing attention due to their advantages in fast charge/dischar... more Supercapacitors (SCs) have drawn growing attention due to their advantages in fast charge/discharge over batteries. Benefiting from their prominent electrical conductivity and metal-like characteristics, transition metal nitrides have emerged as promising electrode materials for SCs. Traditional ways to prepare metal nitrides through ammonolysis are inconvenient and induce severe environmental pollution. Herein, we report a facile synthetic method toward heterogenous Ni 3 N-Co 2 N 0.67 /nitrogen-doped carbon (Ni 3 N-Co 2 N 0.67 /NC) hollow nanoflower via pyrolyzing NiCo-TEOA (triethanolamine) complex precursor applying urea as nitrogen source. Electrochemical tests demonstrate that the Ni 3 N-Co 2 N 0.67 /NC nanoflower delivers good specific capacitance (1582 F g-1 at 1 A g-1) and steady cycle performance (83.79% after 5000 cycles). Moreover, the as-assembled Ni 3 N-Co 2 N 0.67 /NC//AC cell can reach a peak energy density of 32.4 W h kg-1 at a power density of 851.3 W kg-1. The excellent electrochemical performance confirms extensive application prospects of the Ni 3 N-Co 2 N 0.67 /NC nanoflower.

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Microstructures, 2023

NaNbO 3-based lead-free energy storage ceramics are essential candidates for next-generation puls... more NaNbO 3-based lead-free energy storage ceramics are essential candidates for next-generation pulsed power capacitors, especially under the background of energy saving and environmental protection. However, the roomtemperature antiferroelectric P phase of pure NaNbO 3 ceramics limits its further development in energy storage owing to the irreversible antiferroelectric to ferroelectric phase transition under electric fields. In this work, CaZrO 3 was introduced to NaNbO 3 ceramics to destroy the long-range polarization ordering but keep large antiferrodistortion, causing the formation of superparaelectric state with macrodomains, which can be identified by the refinement results of high-energy synchrotron X-ray diffraction, neutron diffraction and TEM results. Combined with the fine grains, dense and homogeneous microstructure, ergodic relaxation behaviors, and delayed polarization saturation, a high recoverable energy storage density of ~5.4 J/cm 3 and efficiency of ~82% can be realized in 0.85NaNbO 3-0.15CaZrO 3 ceramics at an ultrahigh breakdown electric field of ~68 kV/mm. The results found in this work suggest that the supersparaelectric with non-cubic phase would be a good candidate for generating excellent dielectric energy storage properties.

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Microstructures, 2023

The development of dielectric capacitors with high energy density and energy efficiency is of gre... more The development of dielectric capacitors with high energy density and energy efficiency is of great significance in the modern electronic components market. To reduce the high energy loss of Bi0.5Na0.5TiO3, 0.55Bi0.5Na0.5TiO3-0.45(Sr0.7Bi0.2)TiO3 (BNT-BST) nanofibers with a high aspect ratio are synthesized via electrospinning. To achieve a high energy density, the design of a symmetric trilayer nanocomposite consisting of a BNT-BST/polyvinylidene difluoride (PVDF) layer with a high dielectric constant sandwiched between two layers of pure PVDF is herein described. The trilayer structure can effectively alleviate the electric field concentration effect, resulting in a considerably enhanced breakdown strength and improved discharge energy density. The maximum discharge energy density of 17.37 J/cm3 at 580 kV/mm could be achieved in the symmetric trilayer nanocomposite with a BNT-BST/PVDF middle layer, which is 90.5% greater than that achieved using pure PVDF (9.21 J/cm3 at 450 kV/mm). This study presents a new case for developing dielectric capacitors with high energy density.

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Microstructures, 2023

Antiferroelectrics are a kind of unique dielectric materials, mainly due to their polarization be... more Antiferroelectrics are a kind of unique dielectric materials, mainly due to their polarization behavior, and composition-induced antiferroelectricity stability also draws considerable attention. In this work, single orthorhombic phase (Pb0.95Bi0.05)ZrO3 (PBZ), Pb(Zr0.95Bi0.05)O3 (PZB), and PbZrO3 (PZO) films with good density and flatten surface was prepared on Pt/Ti/SiO2/Si substrate via sol-gel method. Compared with pure PZO films, the PBZ and PZB films possess increased switching electric field difference Δ E due to enhanced forward switching field and the late response of backward switching field. In terms of stabilizing AFE phase, changing the tolerance factor t has the similar effect as Bi-doping the A/B sites in PZO, with the modification of the A-site being more effective than that of the B-site. PBZ films achieve a high recoverable energy density (Wrec) of 26.4 J/cm3 with energy efficiency (η) of 56.2% under an electric field of 1278 kV/cm, which exceeds other pure AFE materials. This work provides a fundamental understanding of the crystal structure-related antiferroelectricity of PZO materials and broadens the chemical doping route to enhance the electric properties of AFE materials.

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Microstructures, 2023

High entropy alloys (HEAs), as a new class of structural materials, have attracted extensive inte... more High entropy alloys (HEAs), as a new class of structural materials, have attracted extensive interest from numerous metallurgical scientists and engineers. Benefiting from their unique microstructural features and outstanding mechanical performance, HEAs have shown significant potential for applications in many engineering fields, even under extreme conditions. In particular, when exposed to hydrogen and/or intermediate-temperature environments, these HEAs inevitably suffer from severe environmental embrittlement (EE) issues, e.g., hydrogen embrittlement (HE) and intermediate-temperature embrittlement (ITE), resulting in serious premature intergranular failure. In this work, we critically review the state-of-the-art advances of EE in previously reported HEA systems. Particular focus is given to novel strategies to enhance the resistance to EE in different HEAs. Two critical embrittlement phenomena, namely, HE and ITE, are highlighted separately. Finally, we provide perspectives on future research directions and opportunities for EE-resistant HEAs.

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Microstructures, 2023

Broadband photodetectors covering the ultraviolet (UV) to visible range are significant for appli... more Broadband photodetectors covering the ultraviolet (UV) to visible range are significant for applications in communication and imaging. Broadband photodetectors with the capacity to distinguish wavelength bands are highly desirable because they can provide additional spectral information. Herein, we report a UV-visible distinguishable broadband photodetector based on a graphene/ZnO quantum dot heterostructure. The photodetector exhibits negative photoconductance under visible illumination because the adsorbents on graphene act as scattering centers to reduce the carrier mobility. In contrast, under UV illumination, the photodetector shows positive photoconductance as the photogenerated electrons in the ZnO quantum dots transfer to the graphene, thereby increasing the conductivity. Thus, the detection and distinction of UV and visible illumination can be realized by utilizing the opposing photoconductivity changes. These results offer inspiration for the design of multifunctional broadband photodetectors.

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Microstructures, 2022

Ultrafine-grained (UFG) metallic materials processed by severe plastic deformation (SPD) techniqu... more Ultrafine-grained (UFG) metallic materials processed by severe plastic deformation (SPD) techniques often exhibit significantly higher strengths than those calculated by the well-known Hall-Petch equation. These higher strengths result from the fact that SPD processing not only forms the UFG structure but also leads to the formation of other nanostructural features, including dislocation substructures, nanotwins and nanosized second-phase precipitations, which further contribute to the hardening. Moreover, the analysis of strengthening mechanisms in recent studies demonstrates an important contribution to the hardening due to phenomena related to the structure of grain boundaries as a non-equilibrium state and the presence of grain boundary segregations. Herein, the principles of the nanostructural design of metallic materials for superior strength using SPD processing are discussed.

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Microstructures, 2022

Commentary to publications by Prof. Jun Chen, University of Science and Technology Beijing, E-mai... more Commentary to publications by Prof. Jun Chen, University of Science and Technology Beijing, E-mail: junchen@ustb.edu.cn (10.1038/s41467-022-30821-7; 10.1016/j.actamat.2022.118115).

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Microstructures, 2022

Dielectric capacitors with ultrafast charge-discharge rates are extensively used in electrical an... more Dielectric capacitors with ultrafast charge-discharge rates are extensively used in electrical and electronic systems. To meet the growing demand for energy storage applications, researchers have devoted significant attention to dielectric ceramics with excellent energy storage properties. As a result, the awareness of the importance of the pulsed discharge behavior of dielectric ceramics and conducting characterization studies has been raised. However, the temperature stability of pulsed discharge behavior, which is significant for pulsed power applications, is still not given the necessary consideration. Here, we systematically investigate the microstructures, energy storage properties and discharge behaviors of nanograined (1-x)BaTiO3-xNaNbO3 ceramics prepared by a two-step sintering method. The 0.60BaTiO3-0.40NaNbO3 ceramics with relaxor ferroelectric characteristics possess an optimal discharge energy density of 3.07 J cm-3, a high energy efficiency of 92.6%, an ultrafast discharge rate of 39 ns and a high power density of 100 MW cm-3. In addition to stable energy storage properties in terms of frequency, fatigue and temperature, the 0.60BaTiO3-0.40NaNbO3 ceramics exhibit temperature-stable power density, thereby illustrating their significant potential for power electronics and pulsed power applications.

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Microstructures, 2022

Utilizing clean energy derived from photoelectrocatalytic reactions is expected to be an excellen... more Utilizing clean energy derived from photoelectrocatalytic reactions is expected to be an excellent choice to fundamentally solve the problem of the human energy crisis. Photoelectrochemical (PEC) cell can effectively promote charge separation and improve solar energy conversion efficiency since it combines the advantages of photocatalysis and electrocatalysis. However, the hole transfer and subsequent oxidation reaction in the PEC process are slow, resulting in the rapid recombination of photogenerated electron-hole pairs and low PEC performance. The half-oxidation reaction involving photogenerated holes is the bottleneck of PEC water splitting. Therefore, hole modulation has been an important research area in the field of catalysis. However, compared with electron modulation, research on hole modulation is limited and still faces great challenges. It is therefore of great significance to develop effective modulation strategies for photogenerated holes. This review summarizes the hole modulation strategies developed in the last five years, including hole sacrificial agents, nanostructural modification, heterostructure construction and cocatalyst modification. Hole modulation dynamics studies, such as transient absorption spectroscopy, time-resolved photoluminescence spectroscopy, transient photovoltage and scanning electrochemical microscopy, are also summarized. Moreover, relevant conclusions and an outlook are proposed.

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Microstructures, 2022

Understanding the dynamic behavior of domain structures is critical to the design and application... more Understanding the dynamic behavior of domain structures is critical to the design and application of super-elastic freestanding ferroelectric thin films. Phase-field simulations represent a powerful tool for observing, exploring and revealing the domain-switching behavior and phase transitions in ferroelectric materials at the mesoscopic scale. This review summarizes the recent theoretical progress regarding phase-field methods in freestanding ferroelectric thin films and novel buckling-induced wrinkled and helical structures. Furthermore, the strong coupling relationship between strain and ferroelectric polarization in super-elastic ferroelectric nanostructures is confirmed and discussed, resulting in new design strategies for the strain engineering of freestanding ferroelectric thin film systems. Finally, to further promote the innovative development and application of freestanding ferroelectric thin film systems, this review provides a summary and outlook on the theoretical modeling of freestanding ferroelectric thin films.

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Microstructures, 2022

Although near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are desired for non... more Although near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are desired for non-visible light source applications, the design of broadband NIR phosphors remains a challenge. Inspired by the chemical unit co-substitution strategy for the modification of composition and local structure, we realize a tunable redshift emission from 706 to 765 nm in garnet-type Lu3Sc2Ga3O12:Cr3+ with a broadened full width at half maximum and enhanced photoluminescence intensity by introducing a [Mg2+-Si4+] unit into the [Sc3+-Ga3+] couple. Structural and spectral analyzes demonstrate that the co-substitution reduces the local symmetry and crystal field strength of the [CrO6] octahedra, thus leading to inhomogeneous widening of the 4T2→4A2 emission and enhanced blue absorption. Furthermore, the 4T2→4A2 emission exhibits a phonon-assisted character at low temperatures due to the thermal coupling effect with the 2E level. The fabricated NIR pc-LED based on the optimized NIR phosphor exhibits excellent potential in night vision and imaging applications.

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Microstructures, 2022

β-solidifying TiAl alloys are considered as promising candidate materials for high-temperature st... more β-solidifying TiAl alloys are considered as promising candidate materials for high-temperature structural applications. Laser-based additive manufacturing (LAM) enables the fabrication of components with geometrical complexity in near-net shape, leading to time and feedstock savings. In this study, a gas-atomized Ti-44Al-4Nb-1Mo-1Cr powder is used as a feedstock material for LAM. However, the LAM of TiAl alloys remains a challenge due to serious cracking during the printing process. To minimize the cracking, the optimization of the LAM processing parameters is essential. Hence, the effects of the LAM processing parameters on the cracking susceptibility and microstructure are studied here. Our experimental results show that the cracking susceptibility can be mitigated by increasing the laser power. Accordingly, the microstructure transforms from the dominating α2 grains to a near-lamellar microstructure with an increment in laser power, leading to a reduction in microhardness, even though it is still higher than that of its as-cast counterparts. It is concluded that changes in the laser power can directly tailor the microstructure, phase composition and microhardness of LAM-fabricated TiAl alloys.

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Microstructures, 2022

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Microstructures, 2022

Materials with tunable negative thermal expansion (NTE) are highly demanded in various functional... more Materials with tunable negative thermal expansion (NTE) are highly demanded in various functional devices. La(Fe, Si)13-based compounds are promising NTE materials due to their outstanding NTE properties. However, their poor mechanical properties and related short service life restrict their practical applications. In this work, epoxy resin with positive thermal expansion is used to synthesize La-Fe-Si/resin composites. The NTE of La-Fe-Si/resin composites can be manipulated by optimizing the La-Fe-Si particle size and resin content, and tailoring resin content could tune the NTE more effectively. The average linear coefficient of thermal expansion of the composites decreases from -275.0 × 10-6 K-1 to -4.9 × 10-6 K-1 over the magnetic transition temperature range as the resin content increases from 3 wt.% to 80 wt.%. In addition, zero thermal expansion is achieved in the La-Fe-Si/resin composite with 20 wt.% resin. The resin would reinforce the binding force by filling the pores between the particles. The La-Fe-Si/resin composite with 80 wt.% resin exhibits highly improved mechanical properties; for example, its compressive strength of 205 MPa is 75% higher than that of the La-Fe-Si/resin composite with 3 wt.% resin. The prepared La-Fe-Si/resin composites can be machined into different shapes for practical applications, such as thin plates, strips, and rods. Furthermore, the La-Fe-Si/resin composites can undergo 1000 thermal cycles without NTE performance degradation and mechanical integrity loss, indicating durable cycle stability. Hence, significantly tunable NTE with high mechanical properties and long-term cycle stability makes La-Fe-Si/resin composites present great application potential as NTE materials.

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Microstructures, 2022

Extensive experiments have shown that the transformation from the face-centered cubic to hexagona... more Extensive experiments have shown that the transformation from the face-centered cubic to hexagonal close-packed ε phase usually occurs around coherent Σ3 boundaries. However, in this letter, we reveal a different transformation mechanism in a metastable dual-phase compositionally complex alloy via a systematic high-resolution scanning transmission electron microscopy analysis. The face-centered cubic γ matrix can be transformed to the hexagonal close-packed ɛ phase (as small as one unit) around an incoherent Σ3 boundary (~30 nm), i.e., the facet of the coherent Σ3 boundary. This transformation is assisted by the detwinning/twin growth of a coherent Σ3 boundary during annealing treatment (900 °C for 60 min).

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Microstructures, 2022

Lithium-ion batteries have made significant commercial and academic progress in recent decades. Z... more Lithium-ion batteries have made significant commercial and academic progress in recent decades. Zinc oxide (ZnO) has been widely studied as a lithium-ion battery anode due to its high theoretical capacity of 987 mAh g-1, natural abundance, low cost, and environmental friendliness. However, ZnO suffers from poor electronic conductivity and large volume variation during the battery discharge/charge process, leading to capacity deterioration during long-term cycling. Herein, porous ZnO@C nanoplates are developed to offer short ion diffusion pathways and good conduction networks for both Li ions and electrons. The porous nanoplates provide abundant active sites for electrochemical reactions with minimized charge transfer impedance. As a result, the porous ZnO@C nanoplates deliver higher performance for lithium-ion storage compared with a bare ZnO anode. Furthermore, with the introduction of reduced graphene oxide (rGO), the ZnO@C@rGO composite anode achieves a capacity of 229.3 mAh g-1 at a high current density of 2 A g-1.

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Microstructures, 2022

The effects of cold rolling and subsequent annealing on the microstructures and mechanical proper... more The effects of cold rolling and subsequent annealing on the microstructures and mechanical properties of Fe40Mn20Cr20Ni20 high-entropy alloys (HEAs) are investigated. The Cr-rich secondary phases with a tetragonal structure (σ phases) in the Fe40Mn20Cr20Ni20 HEAs are precipitated upon annealing at 600 °C-900 °C for 2 h. The prepared Fe40Mn20Cr20Ni20 HEA annealed at 800 °C for 2 h after cold rolling has a good combination of strength and elongation, with a high yield strength of 438 MPa, a high ultimate tensile strength of 676 MPa, and an excellent elongation to fracture of 32%. The mechanical properties at cryogenic temperature are better than those at room temperature. Typically, for the incompletely recrystallized alloy annealed at 700 °C, the yield strength, tensile strength, and elongation after fracture are increased by 26%, 22%, and 100%, respectively. This trend mainly depends on dislocation and twinning strengthening. The σ phases also improve the cryogenic tensile properties. Furthermore, the recrystallization kinetics of the Fe40Mn20Cr20Ni20 HEAs are explored to correlate with the deformation behavior.

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