Showing papers in "Journal of Advanced Ceramics in 2022"
TL;DR: In this article , the effects of microwave dielectric ceramics on their microstructures, sintering behaviors, and microwave die-lectric properties were systematically investigated using the Phillips-Van Vechten-Levine (PV-L) theory.
Abstract: Abstract Dense microwave dielectric ceramics of Ce 2 [Zr 1 − x (Al 1/2 Ta 1/2 ) x ] 3 (MoO 4 ) 9 (CZMAT) ( x = 0.02–0.10) were prepared by the conventional solid-state route. The effects of (Al 1/2 Ta 1/2 ) 4+ on their microstructures, sintering behaviors, and microwave dielectric properties were systematically investigated. On the basis of the X-ray diffraction (XRD) results, all the samples were matched well with Pr 2 Zr 3 (MoO 4 ) 9 structures, which belonged to the space group $$R\bar 3c$$ R 3 ¯ c . The lattice parameters were obtained using the Rietveld refinement method. The correlations between the chemical bond parameters and microwave dielectric properties were calculated and analyzed by using the Phillips—Van Vechten—Levine (P—V—L) theory. Excellent dielectric properties of Ce 2 [Zr 0.94 (Al 1/2 Ta 1/2 ) 0.06 ] 3 (MoO 4 ) 9 with a relative permittivity ( ε r ) of 10.46, quality factor ( Q × f ) of 83,796 GHz, and temperature coefficient of resonant frequency ( τ f ) of −11.50 ppm/°C were achieved at 850 °C.
81 citations
TL;DR: In this article , a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth, ceramic sintering, erosion, and calcium-magnesium-aluminium-silicate (CMAS) molten salt corrosion.
Abstract: Abstract Thermal barrier coatings (TBCs) can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat. However, the continuous pursuit of a higher operating temperature leads to degradation, delamination, and premature failure of the top coat. Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems. In this paper, the latest progress of some new ceramic materials is first reviewed. Then, a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth, ceramic sintering, erosion, and calcium-magnesium-aluminium-silicate (CMAS) molten salt corrosion. Finally, new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar, columnar, and nanostructure inclusions. The latest developments of ceramic top coat will be presented in terms of material selection, structural design, and failure mechanism, and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance, better thermal insulation, and longer lifetime.
59 citations
TL;DR: In this article , a high-entropy spinel oxide was used as the cathode for proton-conducting solid oxide fuel cells (H-SOFCs) to achieve an encouraging peak power density (PPD) of 1052 mW·cm −2 at 700 °C.
Abstract: Abstract A high-entropy ceramic oxide is used as the cathode for the first time for proton-conducting solid oxide fuel cells (H-SOFCs). The Fe 0.6 Mn 0.6 Co 0. 6 Ni 0.6 Cr 0.6 O 4 (FMCNC) high-entropy spinel oxide has been successfully prepared, and the in situ chemical stability test demonstrates that the FMCNC material has good stability against CO 2 . The first-principles calculation indicates that the high-entropy structure enhances the properties of the FMCNC material that surpasses their individual components, leading to lower O 2 adsorption energy for FMCNC than that for the individual components. The H-SOFC using the FMCNC cathode reaches an encouraging peak power density (PPD) of 1052 mW·cm −2 at 700 °C, which is higher than those of the H-SOFCs reported recently. Additional comparison was made between the high-entropy FMCNC cathode and the traditional Mn 1. 6 Cu 1.4 O 4 (MCO) spinel cathode without the high-entropy structure, revealing that the formation of the high-entropy material allows the enhanced protonation ability as well as the movement of the O p-band center closer to the Fermi level, thus improving the cathode catalytic activity. As a result, the high-entropy FMCNC has a much-decreased polarization resistance of 0.057 Ω·cm 2 at 700 °C, which is half of that for the traditional MCO spinel cathode without the high-entropy design. The excellent performance of the FMCNC cell indicates that the high-entropy design makes a new life for the spinel oxide as the cathode for H-SOFCs, offering a novel and promising route for the development of high-performance materials for H-SOFCs.
52 citations
TL;DR: In this article , a facile one-step molten salt method for the preparation of self-supporting Ni-doped Mo 2 C on carbon fiber paper (Ni-Mo 2 C CB /CFP) for hydrogen evolution reaction (HER) was investigated.
Abstract: Abstract Developing highly efficient and stable non-precious metal catalysts for water splitting is urgently required. In this work, we report a facile one-step molten salt method for the preparation of self-supporting Ni-doped Mo 2 C on carbon fiber paper (Ni-Mo 2 C CB /CFP) for hydrogen evolution reaction (HER). The effects of nickel nitrate concentration on the phase composition, morphology, and electrocatalytic HER performance of Ni-doped Mo 2 C@CFP electrocatalysts was investigated. With the continuous increase of Ni(NO 3 ) 2 concentration, the morphology of Mo 2 C gradually changes from granular to flower-like, providing larger specific surface area and more active sites. Doping nickel (Ni) into the crystal lattice of Mo 2 C largely reduces the impedance of the electrocatalysts and enhances their electrocatalytic activity. The as-developed Mo 2 C-3 M Ni(NO 3 ) 2 /CFP electrocatalyst exhibits high catalytic activity with a small overpotential of 56 mV at a current density of 10 mA·cm −2 . This catalyst has a fast HER kinetics, as demonstrated by a very small Tafel slope of 27.4 mV·dec −1 , and persistent long-term stability. A further higher Ni concentration had an adverse effect on the electrocatalytic performance. Density functional theory (DFT) calculations further verified the experimental results. Ni doping could reduce the binding energy of Mo-H, facilitating the desorption of the adsorbed hydrogen (H ads ) on the surface, thereby improving the intrinsic catalytic activity of Ni-doped Mo 2 C-based catalysts. Nevertheless, excessive Ni doping would inhibit the catalytic activity of the electrocatalysts. This work not only provides a simple strategy for the facile preparation of non-precious metal electrocatalysts with high catalytic activity, but also unveils the influence mechanism of the Ni doping concentration on the HER performance of the electrocatalysts from the theoretical perspective.
51 citations
TL;DR: In this paper , the authors have shown that a little CuO can form p-n heterojunctions with In 2 O 3 and react with H 2 S, resulting in significant improvement of gas sensing performance.
Abstract: Abstract One-dimensional nanofibers can be transformed into hollow structures with larger specific surface area, which contributes to the enhancement of gas adsorption. We firstly fabricated Cu-doped In 2 O 3 (Cu-In 2 O 3 ) hollow nanofibers by electrospinning and calcination for detecting H 2 S. The experimental results show that the Cu doping concentration besides the operating temperature, gas concentration, and relative humidity can greatly affect the H 2 S sensing performance of the In 2 O 3 -based sensors. In particular, the responses of 6%Cu-In 2 O 3 hollow nanofibers are 350.7 and 4201.5 to 50 and 100 ppm H 2 S at 250 °C, which are over 20 and 140 times higher than those of pristine In 2 O 3 hollow nanofibers, respectively. Moreover, the corresponding sensor exhibits excellent selectivity and good reproducibility towards H 2 S, and the response of 6%Cu-In 2 O 3 is still 1.5 to 1 ppm H 2 S. Finally, the gas sensing mechanism of Cu-In2O3 hollow nanofibers is thoroughly discussed, along with the assistance of first-principles calculations. Both the formation of hollow structure and Cu doping contribute to provide more active sites, and meanwhile a little CuO can form p–n heterojunctions with In 2 O 3 and react with H 2 S, resulting in significant improvement of gas sensing performance. The Cu-In 2 O 3 hollow nanofibers can be tailored for practical application to selectively detect H 2 S at lower concentrations.
46 citations
TL;DR: In this article , MoO 3 /TiO 2 /Mo 2 TiC 2 T x hybrids were prepared by the annealing-treated Mo 2TiC 2T x MXene and uniform MoO3 and TiO 2 oxides in-situ grew on Mo 2 T T x layers.
Abstract: Abstract Two-dimensional (2D) transition metal carbide MXene-based materials hold great potentials applied for new electromagnetic wave (EMW) absorbers. However, the application of MXenes in the field of electromagnetic wave absorption (EMA) is limited by the disadvantages of poor impedance matching, single loss mechanism, and easy oxidation. In this work, MoO 3 /TiO 2 /Mo 2 TiC 2 T x hybrids were prepared by the annealing-treated Mo 2 TiC 2 T x MXene and uniform MoO 3 and TiO 2 oxides in-situ grew on Mo 2 TiC 2 T x layers. At the annealing temperature of 300 °C, the minimum reflection loss (RL min ) value of MoO 3 /TiO 2 /Mo 2 TiC 2 T x reaches −30.76 dB (2.3 mm) at 10.18 GHz with a significantly broadening effective absorption bandwidth (EAB) of 8.6 GHz (1.8 mm). The in-situ generated oxides creating numerous defects and heterogeneous interfaces enhance dipolar and interfacial polarizations and optimize the impedance matching of Mo 2 TiC 2 T x . Considering the excellent overall performance, the MoO 3 /TiO 2 /Mo 2 TiC 2 T x hybrids can be a promising candidate for EMA.
43 citations
TL;DR: In this article , four high-entropy perovskite (HEP) RETa 3 O 9 samples were fabricated via a spark plasma sintering (SPS) method, and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating (E/TBC) applications.
Abstract: Abstract Four high-entropy perovskite (HEP) RETa 3 O 9 samples were fabricated via a spark plasma sintering (SPS) method, and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating (E/TBC) applications. The prepared samples maintained low thermal conductivity (1.50 W·m −1 ·K −1 ), high hardness (10 GPa), and an appropriate Young’s modulus (180 GPa), while the fracture toughness increased to 2.5 MPa·m 1/2 . Nanoindentation results showed the HEP ceramics had excellent mechanical properties and good component homogeneity. We analysed the influence of different parameters (the disorder parameters of the electronegativity, ionic radius, and atomic mass, as well as the tolerance factor) of A-site atoms on the thermal conductivity. Enhanced thermal expansion coefficients, combined with a high melting point and extraordinary phase stability, expanded the applications of the HEP RETa 3 O 9 . The results of this study had motivated a follow-up study on tantalate high-entropy ceramics with desirable properties.
43 citations
TL;DR: In this paper , a high-entropy (La 0.2 Nd 0.6 K −1 ) 2 Ce 2 O 7 is designed and synthesized in order to improve the poor thermal expansion property and further reduce the thermal conductivity.
Abstract: Abstract High-entropy oxides (HEOs) are widely researched as potential materials for thermal barrier coatings (TBCs). However, the relatively low thermal expansion coefficient (TEC) of those materials severely restricts their practical application. In order to improve the poor thermal expansion property and further reduce the thermal conductivity, high-entropy (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 ) 2 Ce 2 O 7 is designed and synthesized in this work. The as-prepared multicomponent material is formed in a simple disordered fluorite structure due to the high-entropy stabilization effect. Notably, it exhibits a much higher TEC of approximately 12.0 × 10 −6 K −1 compared with those of other high-entropy oxides reported in the field of TBCs. Besides, it presents prominent thermal insulation behavior with a low intrinsic thermal conductivity of 0.92 W·m −1 ·K −1 at 1400 °C, which can be explained by the existence of high concentration oxygen vacancies and highly disordered arrangement of multicomponent cations in the unique high-entropy configuration. Through high-temperature in-situ X-ray diffraction (XRD) measurement, this material shows excellent phase stability up to 1400 °C. Benefiting from the solid solution strengthening effect, it shows a higher hardness of 8.72 GPa than the corresponding single component compounds. The superior thermo-physical performance above enables (La 0.2 Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 ) 2 Ce 2 O 7 a promising TBC material.
42 citations
TL;DR: In this article , three high-entropy spinel-type ferrite ceramics including (Mg 0.2 Mn 0.1 Zn 0.4 )Fe 2 O 4 were designed and successfully prepared through solid state synthesis, and the results show that all three samples exhibit synergetic dielectric loss and magnetic loss.
Abstract: Abstract Ferrites are the most widely used microwave absorbing materials to deal with the threat of electromagnetic (EM) pollution. However, the lack of sufficient dielectric loss capacity is the main challenge that limits their applications. To cope with this challenge, three high-entropy (HE) spinel-type ferrite ceramics including (Mg 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )Fe 2 O 4 , (Mg 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )Fe 2 O 4 , and (Mg 0.2 Fe 0.2 Co 0.2 Ni 0.2 Zn 0.2 )Fe 2 O 4 were designed and successfully prepared through solid state synthesis. The results show that all three HE MFe 2 O 4 samples exhibit synergetic dielectric loss and magnetic loss. The good magnetic loss ability is due to the presence of magnetic components; while the enhanced dielectric properties are attributed to nano-domain, hopping mechanism of resonance effect and HE effect. Among three HE spinels, (Mg 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )Fe 2 O 4 shows the best EM wave absorption performance, e.g., its minimum reflection loss (RL min ) reaches −35.10 dB at 6.78 GHz with a thickness of 3.5 mm, and the optimized effective absorption bandwidth (EAB) is 7.48 GHz from 8.48 to 15.96 GHz at the thickness of 2.4 mm. Due to the easy preparation and strong EM dissipation ability, HE MFe 2 O 4 are promising as a new type of EM absorption materials.
42 citations
TL;DR: In this paper , a novel Al/Nd co-doping method of Ba 4 Nd 9.33 + z/3 Ti 18− z Al 4 z /3 O 54 (BNT-A, 0 ⩽ z ⌽ 2) was proposed to improve the dielectric properties through structural and defect modulation.
Abstract: Abstract Low-loss tungsten-bronze microwave dielectric ceramics are dielectric materials with potential application value for miniaturized dielectric filters and antennas in the fifth-generation (5G) communication technology. In this work, a novel Al/Nd co-doping method of Ba 4 Nd 9.33 Ti 18 O 54 (BNT) ceramics with a chemical formula of Ba 4 Nd 9.33+ z /3 Ti 18− z Al z O 54 (BNT-AN, 0 ⩽ z ⩽ 2) was proposed to improve the dielectric properties through structural and defect modulation. Together with Al-doped ceramics (Ba 4 Nd 9.33 Ti 18− z Al 4 z /3 O 54 , BNT-A, 0 ⩽ z ⩽ 2) for comparison, the ceramics were prepared by a solid state method. It is found that Al/Nd co-doping method has a significant effect on improving the dielectric properties compared with Al doping. As the doping amount z increased, the relative dielectric constant ( ε r ) and the temperature coefficient of resonant frequency ( τ f ) of the ceramics decreased, and the Q×f values of the ceramics obviously increased when z ⩽ 1.5. Excellent microwave dielectric properties of ε r = 72.2, Q×f = 16,480 GHz, and τ f = +14.3 ppm/°C were achieved in BNT-AN ceramics with z = 1.25. Raman spectroscopy and thermally stimulated depolarization current (TSDC) technique were firstly combined to analyze the structures and defects in microwave dielectric ceramics. It is shown that the improvement on Q×f values was originated from the decrease in the strength of the A-site cation vibration and the concentration of oxygen vacancies ( $${\rm{V}}_{\rm{O}}^{ \cdot \cdot }$$ V O ⋅ ⋅ ), demonstrating the effect and mechanism underlying for structural and defect modulation on the performance improvement of microwave dielectric ceramics.
37 citations
TL;DR: In this paper , a lead-free solid solution, (1− x )NaNbO 3 − x Bi(Zn 0.5 Sn 0.20 )O 3 (abbreviated as x BZS, x = 0.10, 0.15, and 0.17), was designed to analyze the domain evolution and relaxor behavior, which confirmed the contribution of the relaxor behaviour to their decent energy storage characteristics caused by the low energy barrier of polar nanoregions (PNRs).
Abstract: Abstract Ceramic dielectric capacitors have a broad scope of application in pulsed power supply devices. Relaxor behavior has manifested decent energy storage capabilities in dielectric materials due to its fast polarization response. In addition, an ultrahigh energy storage density can also be achieved in NaNbO 3 (NN)-based ceramics by combining antiferroelectric and relaxor characteristics. Most of the existing reports about lead-free dielectric ceramics, nevertheless, still lack the relevant research about domain evolution and relaxor behavior. Therefore, a novel lead-free solid solution, (1− x )NaNbO 3 − x Bi(Zn 0.5 Sn 0.5 )O 3 (abbreviated as x BZS, x = 0.05, 0.10, 0.15, and 0.20) was designed to analyze the domain evolution and relaxor behavior. Domain evolutions in x BZS ceramics confirmed the contribution of the relaxor behavior to their decent energy storage characteristics caused by the fast polarization rotation according to the low energy barrier of polar nanoregions (PNRs). Consequently, a high energy storage density of 3.14 J/cm 3 and energy efficiency of 83.30% are simultaneously available with 0.10BZS ceramics, together with stable energy storage properties over a large temperature range (20–100 °C) and a wide frequency range (1–200 Hz). Additionally, for practical applications, the 0.10BZS ceramics display a high discharge energy storage density ( W dis ≈ 1.05 J/cm 3 ), fast discharge rate ( t 0.9 ≈ 60.60 ns), and high hardness ( H ≈ 5.49 GPa). This study offers significant insights on the mechanisms of high performance lead-free ceramic energy storage materials.
TL;DR: In this article , a soft template method was used to detect low concentrations of volatile organic compounds (VOCs) for the early diagnosis of lung cancer, sensors based on hollow spheres of In 2 O 3 were prepared through the soft template technique.
Abstract: Abstract In order to detect low concentrations of volatile organic compounds (VOCs) for the early diagnosis of lung cancer, sensors based on hollow spheres of In 2 O 3 were prepared through the soft template method. Ag nanoparticle decorated In 2 O 3 composites were synthesized via dipping and annealing. The microstructure, phase composition, element distribution, and state of Ag were analyzed by the scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The gas sensing tests showed that Ag-In 2 O 3 sensors had the highest response to isopropanol at 300 °C. The best response of Ag-In 2 O 3 composite sensor was 5.2, which had a significant improvement compared with only In 2 O 3 . Moreover, the response and recovery time of Ag-In 2 O 3 composite sensor was significantly shortened. The improved sensing properties of Ag-In 2 O 3 composite sensor could be attributed to the Schottky barrier created at Ag-In 2 O 3 interface and catalytical effect of Ag.
TL;DR: In this paper , the effects of various electrode parameters including the electrode porosity, active material particle diameter, electrode electronic conductivity, electrode thickness, line width, and pore size on the electrochemical performance were investigated.
Abstract: Abstract Three-dimensional (3D) grid porous electrodes introduce vertically aligned pores as a convenient path for the transport of lithium-ions (Li-ions), thereby reducing the total transport distance of Li-ions and improving the reaction kinetics. Although there have been other studies focusing on 3D electrodes fabricated by 3D printing, there still exists a gap between electrode design and their electrochemical performance. In this study, we try to bridge this gap through a comprehensive investigation on the effects of various electrode parameters including the electrode porosity, active material particle diameter, electrode electronic conductivity, electrode thickness, line width, and pore size on the electrochemical performance. Both numerical simulations and experimental investigations are conducted to systematically examine these effects. 3D grid porous Li 4 Ti 5 O 12 (LTO) thick electrodes are fabricated by low temperature direct writing technology and the electrodes with the thickness of 1085 µm and areal mass loading of 39.44 mg·cm −2 are obtained. The electrodes display impressive electrochemical performance with the areal capacity of 5.88 mAh·cm −2 @1.0 C, areal energy density of 28.95 J·cm −2 @1.0 C, and areal power density of 8.04 mW·cm −2 @1.0 C. This study can provide design guidelines for obtaining 3D grid porous electrodes with superior electrochemical performance.
TL;DR: In this paper , a new high-speed positive grinding strategy combined with solid-state reaction method was used to obtain high-entropy rare-earth zirconate (SZIR) ceramics.
Abstract: Abstract The high-entropy rare-earth zirconate ((La 0.2 Nd 0.2 Sm 0.2 Gd 0.2 Yb 0.2 ) 2 Zr 2 O 7 , 5RE 2 Zr 2 O 7 HEREZs) ceramics were successfully prepared by a new high-speed positive grinding strategy combined with solid-state reaction method. The microstructure, crystal structure, phase composition, and thermophysical and mechanical properties of the samples were systematically investigated through various methods. Results indicate that the samples have a single-phase defect fluorite-type crystal structure with excellent high-temperature thermal stability. The as-prepared samples also demonstrate low thermal conductivity (0.9–1.72 W·m −1 ·K −1 at 273–1273 K) and high coefficient of thermal expansion (CTE, 10.9 × 10 −6 K −1 at 1273 K), as well as outstanding mechanical properties including large Young’s modulus ( E = 186–257 GPa) and high fracture toughness ( K IC ). Furthermore, the formation possibility of the as-prepared samples was verified through the first-principles calculations, which suggested the feasibility to form the 5RE 2 Zr 2 O 7 HE-REZs in the thermodynamic direction. Therefore, in view of the excellent multifunctional properties exhibited by the as-prepared 5RE 2 Zr 2 O 7 HE-REZs, they have great potential applications in next-generation thermal-barrier coatings (TBCs).
TL;DR: In this paper , two high-entropy transition metal carbides (HE TMCs) including (Zr,Hf,Nb,Ta)C and (Cr, Zr, Hf, Nb, Ta)C were designed and synthesized, of which the microwave absorption performance was investigated in comparison with previously reported (Ti,Zr and Ta).
Abstract: Abstract Electronic devices pervade everyday life, which has triggered severe electromagnetic (EM) wave pollution. To face this challenge, developing EM wave absorbers with ultra-broadband absorption capacity is critically required. Currently, nano-composite construction has been widely utilized to realize impedance match and broadband absorption. However, complex experimental procedures, limited thermal stability, and interior oxidation resistance are still unneglectable issues. Therefore, it is appealing to realize ultra-broadband EM wave absorption in single-phase materials with good stability. Aiming at this target, two high-entropy transition metal carbides (HE TMCs) including (Zr,Hf,Nb,Ta)C (HE TMC-2) and (Cr,Zr,Hf,Nb,Ta)C (HE TMC-3) are designed and synthesized, of which the microwave absorption performance is investigated in comparison with previously reported (Ti,Zr,Hf,Nb,Ta)C (HE TMC-1). Due to the synergistic effects of dielectric and magnetic losses, HE TMC-2 and HE TMC-3 exhibit better impedance match and wider effective absorption bandwidth (EAB). In specific, the exclusion of Ti element in HE TMC-2 endows it optimal minimum reflection loss (RL min ) and EAB of −41.7 dB (2.11 mm, 10.52 GHz) and 3.5 GHz (at 3.0 mm), respectively. Remarkably, the incorporation of Cr element in HE TMC-3 significantly improves the impedance match, thus realizing EAB of 10.5, 9.2, and 13.9 GHz at 2, 3, and 4 mm, respectively. The significance of this study lays on realizing ultra-broadband capacity in HE TMC-3 (Cr, Zr, Hf, Nb, Ta), demonstrating the effectiveness of high-entropy component design in tailoring the impedance match.
TL;DR: In this paper , a review of polymer-derived ceramics in terms of synthesis, processing, and microstructure characterization is provided, followed by a summary of PDCs used in energy conversion systems (mainly in gas turbine engines), including fundamentals and material issues.
Abstract: Abstract Since the 1960s, a new class of Si-based advanced ceramics called polymer-derived ceramics (PDCs) has been widely reported because of their unique capabilities to produce various ceramic materials (e.g., ceramic fibers, ceramic matrix composites, foams, films, and coatings) and their versatile applications. Particularly, due to their promising structural and functional properties for energy conversion and storage, the applications of PDCs in these fields have attracted much attention in recent years. This review highlights the recent progress in the PDC field with the focus on energy conversion and storage applications. Firstly, a brief introduction of the Si-based polymer-derived ceramics in terms of synthesis, processing, and microstructure characterization is provided, followed by a summary of PDCs used in energy conversion systems (mainly in gas turbine engines), including fundamentals and material issues, ceramic matrix composites, ceramic fibers, thermal and environmental barrier coatings, as well as high-temperature sensors. Subsequently, applications of PDCs in the field of energy storage are reviewed with a strong focus on anode materials for lithium and sodium ion batteries. The possible applications of the PDCs in Li-S batteries, supercapacitors, and fuel cells are discussed as well. Finally, a summary of the reported applications and perspectives for future research with PDCs are presented.
TL;DR: In this article , a new type of BaTiO 3 /CuO heterostructure catalyst was designed and synthesized to achieve high piezo-photocatalytic activity through the synergy of heterojunction and piezoelectric effect.
Abstract: Abstract Introducing polarization field of piezoelectric materials is an effective strategy to improve photocatalytic performance. In this study, a new type of BaTiO 3 /CuO heterostructure catalyst was designed and synthesized to achieve high piezo-photocatalytic activity through the synergy of heterojunction and piezoelectric effect. The BaTiO 3 /CuO heterostructure shows a significantly enhanced piezo-photocatalytic degradation efficiency of organic pollutants compared with the individual BaTiO 3 nanowires (NWs) and CuO nanoparticles (NPs). Under the co-excitation of ultrasonic vibration and ultraviolet radiation, the optimal degradation reaction rate constant k of polarized BaTiO 3 /CuO heterostructure on methyl orange (MO) dye can reach 0.05 min − 1 , which is 6.1 times of photocatalytic rate and 7 times of piezocatalytic rate. The BaTiO 3 /CuO heterostructure with remarkable piezo-photocatalytic behavior provides a promising strategy for the development of high-efficiency catalysts for wastewater purification, and it also helps understand the coupling mechanism between piezoelectric effect and photocatalysis.
TL;DR: In this paper , a dual-functional composite catalyst for photocatalytic hydrogen evolution and benzaldehyde production was proposed, and a new strategy for preventing the photogenerated electrons and holes from recombining by constructing a 0D/2D heterojunction with increased Schottky barrier (SB) sites.
Abstract: Abstract Converting water into hydrogen fuel and oxidizing benzyl alcohol to benzaldehyde simultaneously under visible light illumination is of great significance, but the fast recombination of photogenerated carriers in photocatalysts seriously decreases the conversion efficiency. Herein, a novel dual-functional 0D Cd 0.5 Zn 0.5 S/2D Ti 3 C 2 hybrid was fabricated by a solvothermally in-situ generated assembling method. The Cd 0.5 Zn 0.5 S nano-spheres with a fluffy surface completely and uniformly covered the ultrathin Ti 3 C 2 nanosheets, leading to the increased Schottky barrier (SB) sites due to a large contact area, which could accelerate the electron-hole separation and improve the light utilization. The optimized Cd 0.5 Zn 0.5 S/Ti 3 C 2 hybrid simultaneously presents a hydrogen evolution rate of 5.3 mmol/(g·h) and a benzaldehyde production rate of 29.3 mmol/(g·h), which are ∼3.2 and 2 times higher than those of pristine Cd 0.5 Zn 0.5 S, respectively. Both the multiple experimental measurements and the density functional theory (DFT) calculations further demonstrate the tight connection between Cd 0.5 Zn 0.5 S and Ti 3 C 2 , formation of Schottky junction, and efficient photogenerated electron—hole separation. This paper suggests a dual-functional composite catalyst for photocatalytic hydrogen evolution and benzaldehyde production, and provides a new strategy for preventing the photogenerated electrons and holes from recombining by constructing a 0D/2D heterojunction with increased SB sites.
TL;DR: In this paper , an A-site defect engineering method was proposed to optimize the electric polarization behavior by disrupting the orderly arrangement of a-site ions, in which the lead-free bulk ceramics showed relatively low recoverable energy storage density (W rec ) especially at low electric field condition.
Abstract: Abstract Lead-free bulk ceramics for advanced pulsed power capacitors show relatively low recoverable energy storage density ( W rec ) especially at low electric field condition. To address this challenge, we propose an A-site defect engineering to optimize the electric polarization behavior by disrupting the orderly arrangement of A-site ions, in which $${\rm{B}}{{\rm{a}}_{0.105}}{\rm{N}}{{\rm{a}}_{0.325}}{\rm{S}}{{\rm{r}}_{0.245 - 1.5x}}{_{0.5x}}{\rm{B}}{{\rm{i}}_{0.325 + x}}{\rm{Ti}}{{\rm{O}}_3}$$ Ba 0.105 Na 0.325 Sr 0.245 − 1.5 x □ 0.5 x Bi 0.325 + x TiO 3 ( $${\rm{BN}}{{\rm{S}}_{0.245 - 1.5x}}{_{0.5x}}{{\rm{B}}_{0.325 + x}}{\rm{T}}$$ BNS 0.245 − 1.5 x □ 0.5 x B 0.325 + x T , x = 0, 0.02, 0.04, 0.06, and 0.08) lead-free ceramics are selected as the representative. The $${\rm{BN}}{{\rm{S}}_{0.245 - 1.5x}}{_{0.5x}}{{\rm{B}}_{0.325 + x}}{\rm{T}}$$ BNS 0.245 − 1.5 x □ 0.5 x B 0.325 + x T ceramics are prepared by using pressureless solid-state sintering and achieve large W rec (1.8 J/cm 3 ) at a low electric field (@110 kV/cm) when x = 0.06. The value of 1.8 J/cm 3 is super high as compared to all other W rec in lead-free bulk ceramics under a relatively low electric field (< 160 kV/cm). Furthermore, a high dielectric constant of 2930 within 15% fluctuation in a wide temperature range of 40–350 °C is also obtained in $${\rm{BN}}{{\rm{S}}_{0.245 - 1.5x}}{_{0.5x}}{{\rm{B}}_{0.325 + x}}{\rm{T}}$$ BNS 0.245 − 1.5 x □ 0.5 x B 0.325 + x T ( x = 0.06) ceramics. The excellent performances can be attributed to the A-site defect engineering, which can reduce remnant polarization ( P r ) and improve the thermal evolution of polar nanoregions (PNRs). This work confirms that the $${\rm{BN}}{{\rm{S}}_{0.245 - 1.5x}}{_{0.5x}}{{\rm{B}}_{0.325 + x}}{\rm{T}}$$ BNS 0.245 − 1.5 x □ 0.5 x B 0.325 + x T ( x = 0.06) ceramics are desirable for advanced pulsed power capacitors, and will push the development of a series of Bi 0.5 Na 0.5 TiO 3 (BNT)-based ceramics with high W rec and high-temperature stability.
TL;DR: In this article , multi-layered piezoelectric composites with a porous structure based on highly oriented Pb(Zr 0.52 Ti 0.48 )O 3 /PVDF (PZT/pVDF) electrospinning fibers are prepared via a laminating method to construct high-performance PENGs.
Abstract: Abstract Piezoelectric nanogenerators (PENGs) that can harvest mechanical energy from ambient environment have broad prospects for multi-functional applications. Here, multi-layered piezoelectric composites with a porous structure based on highly oriented Pb(Zr 0.52 Ti 0.48 )O 3 /PVDF (PZT/PVDF) electrospinning fibers are prepared via a laminating method to construct high-performance PENGs. PZT particles as piezoelectric reinforcing phases are embedded in PVDF fibers and facilitate the formation of polar β phase in PVDF. The multi-layered, porous structure effectively promotes the overall polarization and surface bound charge density, resulting in a highly efficient electromechanical conversion. The PENG based on 10 wt% PZT/PVDF composite fibers with a 220 µm film thickness outputs an optimal voltage of 62.0 V and a power of 136.9 µW, which are 3.4 and 6.5 times those of 10 wt% PZT/PVDF casting film-based PENG, respectively. Importantly, the PENG shows a high sensitivity of 12.4 V·N −1 , presenting a significant advantage in comparison to PENGs with other porous structures. In addition, the composites show excellent flexibility with a Young’s modulus of 227.2 MPa and an elongation of 262.3%. This study shows a great potential application of piezoelectric fiber composites in flexible energy harvesting devices.
TL;DR: In this article , a series of high-entropy perovskite oxides (HEPOs) were synthesized by coprecipitation method combined with calcination process and explored as electrodes for supercapacitors.
Abstract: Abstract A series of high-entropy perovskite oxides (HEPOs) La(CoCrFeMnNiAl x ) 1/(5+ x ) O 3− δ ( x = 0.4, 0.5, 0.6, and 0.7) have been synthesized by coprecipitation method combined with calcination process and explored as electrodes for supercapacitors. The crystal structure, microstructure, and elemental composition of HEPOs were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) in detail. The electrochemical properties of HEPOs as supercapacitor electrodes were elucidated. The specific capacitances of HEPOs ( x = 0.4, 0.5, 0.6, and 0.7) are 281.84, 353.65, 325.60, and 259.30 F/g at the current density of 1 A/g, respectively. After 2000 cycles, the specific capacitances of HEPOs ( x = 0.4, 0.5, 0.6, and 0.7) remain 85.01%, 88.61%, 86.37%, and 91.25%, respectively. Such outstanding electrochemical properties can be attributed to the entropy-stabilized structure caused by mixed six cations in B-site and the Al 3+ -doping suppressing active ion aggregation during charge—discharge process. This research highlights the potential of HEPOs as electrodes for supercapacitors.
TL;DR: In this article , a two-step hydrothermal method was used to construct a photocatalytic co-catalyst, where MoO 2 with metallic nature acted as an electron-transport bridge between CdS and Mo 2 C MXene to accelerate the photoinduced electron transferring.
Abstract: Abstract Nowadays, photocatalytic technologies are regarded as promising strategies to solve energy problems, and various photocatalysts have been synthesized and explored. In this paper, a novel CdS/MoO 2 @Mo 2 C-MXene photocatalyst for H 2 production was constructed by a two-step hydrothermal method, where MoO 2 @Mo 2 C-MXene acted as a binary co-catalyst. In the first hydrothermal step, MoO 2 crystals with an egged shape grew on the surface of two-dimensional (2D) Mo 2 C MXene via an oxidation process in HCl aqueous solution. In the second hydrothermal step, CdS nanorods were uniformly assembled on the surface of MoO 2 @Mo 2 C-MXene in ethylenediamine with an inorganic cadmium source and organic sulfur source. The CdS/MoO 2 @Mo 2 C-MXene composite with MoO 2 @Mo 2 C-MXene of 5 wt% exhibits an ultrahigh visible-light photocatalytic H 2 production activity of 22,672 µmol/(g·h), which is ∼21% higher than that of CdS/Mo 2 C-MXene. In the CdS/MoO 2 @Mo 2 C-MXene composite, the MoO 2 with metallic nature separates CdS and Mo 2 C MXene, which acts as an electron-transport bridge between CdS and Mo 2 C MXene to accelerate the photoinduced electron transferring. Moreover, the energy band structure of CdS was changed by MoO 2 @Mo 2 C-MXene to suppress the recombination of photogenerated carriers. This novel compound delivers upgraded photocatalytic H 2 evolution performance and a new pathway of preparing the low-cost photocatalyst to solve energy problems in the future.
TL;DR: In this paper , a simple thermochemical process was used to prepare a multifunctional SiC nanofiber aerogel spring (SiC NFAS), which exhibited ultralow density (9 mg/cm 3 ), ultra-low thermal conductivity (0.029 W/(m·K) at 20 °C), excellent ablation and oxidation resistance, and a stable three-dimensional (3D) structure that composed of a large number of interlacing 3C-SiC Nanofibers with diameters of 300-500 nm and lengths in tens to hundreds of microns.
Abstract: Abstract Multifunctionalization is the development direction of personal thermal energy regulation equipment in the future. However, it is still a huge challenge to effectively integrate multiple functionalities into one material. In this study, a simple thermochemical process was used to prepare a multifunctional SiC nanofiber aerogel spring (SiC NFAS), which exhibited ultralow density (9 mg/cm 3 ), ultralow thermal conductivity (0.029 W/(m·K) at 20 °C), excellent ablation and oxidation resistance, and a stable three-dimensional (3D) structure that composed of a large number of interlacing 3C-SiC nanofibers with diameters of 300–500 nm and lengths in tens to hundreds of microns. Furthermore, the as-prepared SiC NFAS displayed excellent mechanical properties, with a permanent deformation of only 1.3% at 20 °C after 1000 cycles. Remarkably, the SiC NFAS exhibited robust hyperelasticity and cyclic fatigue resistance at both low (∼−196 °C) and high (∼700 °C) temperatures. Due to its exceptional thermal insulation performance, the SiC NFAS can be used for personal thermal energy regulation. The results of the study conclusively show that the SiC NFAS is a multifunctional material and has potential insulation applications in both low- and high-temperature environments.
TL;DR: In this article , a patterned package design and a phosphor wheel was proposed and demonstrated effectively to deal with the challenge of simultaneously achieving good photometric and chromatic performances.
Abstract: Abstract Up-to-date laser-driven lightings confront a challenge of simultaneously achieving good photometric and chromatic performances. Herein, the coupling of “patterned package design” and “phosphor wheel” was proposed and demonstrated effectively to deal with this tough issue, based on a new architecture of CaAlSiN 3 :Eu 2+ (CASN:Eu) glass ceramic film (GCF) on Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce) GC plate. The fabricated composite has no interface between the two functional layers and retains the admirable luminescent features from CASN:Eu and YAG:Ce for the microstructural integrity during co-sintering. The studies on laser-microcrystalline interactions reveal that the luminescence saturation is almost determined by thermal quenching for YAG:Ce, but is ascribed to thermal/intensity quenching which are equally crucial for CASN:Eu. Benefiting from the elaborate architecture design, good color chromaticity tunability was obtained, and severe photon reabsorption was reduced. Moreover, accompanied with the rotation induced increase of thermal convection to air and pulse-like excitation, the constructed lighting engine under blue laser driven shows bright white light with luminous flux (LF) higher than 1000 lm, adjustable chromaticity from cool to warm, and improved color rendering index (CRI) approaching to 70.
TL;DR: In this article , the solid solution mechanism of Sc in the Gd 2 Zr 2 O 7 lattice, and the mechanical and thermophysical properties of the doped Gd2Zr2O7 were systematically studied by the first-principles method, based on which the Sc doping content was optimized.
Abstract: Abstract Sc was doped into Gd 2 Zr 2 O 7 for expanding the potential for thermal barrier coating (TBC) applications. The solid solution mechanism of Sc in the Gd 2 Zr 2 O 7 lattice, and the mechanical and thermophysical properties of the doped Gd2Zr2O7 were systematically studied by the first-principles method, based on which the Sc doping content was optimized. Additionally, Sc-doped Gd 2 Zr 2 O 7 TBCs with the optimized composition were prepared by air plasma spraying using YSZ as a bottom ceramic coating (Gd-Sc/YSZ TBCs), and their sintering behavior and thermal cycling performance were examined. Results revealed that at low Sc doping levels, Sc has a large tendency to occupy the lattice interstitial sites, and when the doping content is above 11.11 at%, Sc substituting for Gd in the lattice becomes dominant. Among the doped Gd 2 Zr 2 O 7 , the composition with 16.67 at% Sc content has the lowest Pugh’s indicator ( G/B ) and the highest Poisson ratio ( σ ) indicative of the highest toughness, and the decreasing trends of Debye temperature and thermal conductivity slow down at this composition. By considering the mechanical and thermophysical properties comprehensively, the Sc doping content was optimized to be 16.67 at%. The fabricated Gd-Sc coatings remain phase and structural stability after sintering at 1400 °C for 100 h. Gd-Sc/YSZ TBCs exhibit excellent thermal shock resistance, which is related to the good thermal match between Gd-Sc and YSZ coatings, and the buffering effect of the YSZ coating during thermal cycling. These results revealed that Sc-doped Gd 2 Zr 2 O 7 has a high potential for TBC applications, especially for the composition with 16.67 at% Sc content.
TL;DR: In this article , a novel 2D graphene oxide (GO) modified α-AgVO 3 nanorods (GO/α-AGVO 3 ) photocatalyst was designed to improve the separation of photocarriers.
Abstract: Abstract Silver vanadates are promising visible-light-responded photocatalysts with suitable bandgap for solar absorption. However, the easy recombination of photogenerated carriers limits their performance. To overcome this obstacle, a novel 2D graphene oxide (GO) modified α-AgVO 3 nanorods (GO/α-AgVO 3 ) photocatalyst was designed herein to improve the separation of photocarriers. The GO/α-AgVO 3 was fabricated through a facile in-situ coprecipitation method at room temperature. It was found that the as-prepared 0.5 wt% GO/α-AgVO 3 exhibited the most excellent performance for rhodamine B (RhB) decomposition, with an apparent reaction rate constant 18 times higher than that of pure α-AgVO 3 under visible-light irradiation. In light of the first-principles calculations and the hetero junction analysis, the mechanism underpinned the enhanced photocatalytic performance was proposed. The enhanced photocatalytic performance was ascribed to the appropriate bandgap of α-AgVO 3 nanorods for visible-light response and efficient separation of photocarriers through GO nanosheets. This work demonstrates the feasibility of overcoming the easy recombination of photogenerated carriers and provides a valuable GO/α-AgVO 3 photocatalyst for pollutant degradation.
TL;DR: In this paper , a pyrochlore component with high-entropy design of Bi 1.5 ZnNb 1.75 O 7 (BZMNT) bulk endows an excellent energy storage performance of W rec ≈ 2.72 J/cm 3 together with an ultra high energy efficiency of 91% at a significant enhanced electric field E b of 650 kV/cm.
Abstract: Abstract High-performance dielectrics are widely used in high-power systems, electric vehicles, and aerospace, as key materials for capacitor devices. Such application scenarios under these extreme conditions require ultra-high stability and reliability of the dielectrics. Herein, a novel pyrochlore component with high-entropy design of Bi 1.5 Zn 0.75 Mg 0.25 Nb 0.75 Ta 0.75 O 7 (BZMNT) bulk endows an excellent energy storage performance of W rec ≈ 2.72 J/cm 3 together with an ultra-high energy efficiency of 91% at a significant enhanced electric field E b of 650 kV/cm. Meanwhile, the temperature coefficient (TCC) of BZMNT (∼ −220 ppm/°C) is also found to be greatly improved compared with that of the pure Bi 1.5 ZnNb 1.5 O 7 (BZN) (∼ −300 ppm/°C), demonstrating its potential application in temperature-reliable conditions. The high-entropy design results in lattice distortion that contributes to the polarization, while the retardation effect results in a reduction of grain size to submicron scale which enhances the E b . The high-entropy design provides a new strategy for improving the high energy storage performance of ceramic materials.
TL;DR: In this paper , a multilayer SiC-Si 3 N 4 matrices were fabricated by chemical vapor infiltration (CVI) to alleviate the mismatch of coefficients of thermal expansion and elastic modulus between carbon fiber and SiC matrix.
Abstract: Abstract Oxidation behaviors of carbon fiber reinforced SiC matrix composites (C/SiC) are one of the most noteworthy properties. For C/SiC, the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion (CTEs) and elastic modulus between carbon fiber and SiC matrix. In order to improve the oxidation resistance, multilayer SiC-Si 3 N 4 matrices were fabricated by chemical vapor infiltration (CVI) to alleviate the above two kinds of mismatch and change the local stress distribution. For the oxidation of C/SiC with multilayer matrices, matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC-Si 3 N 4 matrix to lengthen the oxygen diffusion channels, thereby improving the oxidation resistance of C/SiC, especially at 800 and 1000 °C. The strength retention ratio was increased from 61.9% (C/SiC-SiC/SiC) to 75.7% (C/SiC-Si 3 N 4 /SiC/SiC) and 67.8% (C/SiC-SiC/Si 3 N 4 /SiC) after oxidation at 800 °C for 10 h.
TL;DR: In this article , a microwave dielectric ceramics (MWDCs) with low dielectrics constant and low Dielectric loss are desired in contemporary society, where the communication frequency is developing to high frequency (sub-6G).
Abstract: Microwave dielectric ceramics (MWDCs) with low dielectric constant and low dielectric loss are desired in contemporary society, where the communication frequency is developing to high frequency (sub-6G). Herein, Nd2(Zr1−xTix)3(MoO4)9 (NZ1−xTxM, x = 0.02–0.10) ceramics were prepared through a solid-phase process. According to X-ray diffraction (XRD) patterns, the ceramics could form a pure crystal structure with the R c (167) space group. The internal parameters affecting the properties of the ceramics were calculated and analyzed by employing Clausius–Mossotti relationship, Shannon’s rule, and Phillips–van Vechten–Levine (P–V–L) theory. Furthermore, theoretical dielectric loss of the ceramics was measured and analyzed by a Fourier transform infrared (IR) radiation spectrometer. Notably, when x = 0.08 and sintered at 700 ℃, optimal microwave dielectric properties of the ceramics were obtained, including a dielectric constant (εr) = 10.94, Q·f = 82,525 GHz (at 9.62 GHz), and near-zero resonant frequency temperature coefficient (τf) = −12.99 ppm/℃. This study not only obtained an MWDC with excellent properties but also deeply analyzed the effects of Ti4+ on the microwave dielectric properties and chemical bond characteristics of Nd2Zr3(MoO4)9 (NZM), which laid a solid foundation for the development of rare-earth molybdate MWDC system.