Table of Content

15 May 2024, Volume 53 Issue 5

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Review

Research Progress on the Growth of Silicon Carbide Single Crystal via Top-Seeded Solution Growth Method and Its Key Issues

GU Peng, LEI Pei, YE Shuai, HU Jin, WU Ge

2024, 53(5):  741-759. 

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Due to its excellent physical properties, the third-generation semiconductor silicon carbide (SiC) material has very clear application prospects in the fields of high-temperature, high-frequency, high-pressure, and high-power electronics and RF microwave devices. Limited by its own technical characteristics, using traditional physical vapor transport (PVT) method to prepare SiC crystals still faces many technical challenges, making it difficult to meet the urgent demand for large-size, high-quality, and low-cost SiC single crystal substrates in current electronic devices. Top seed solution (TSSG) can be used to prepare SiC crystal at lower temperatures and near thermodynamic equilibrium conditions, which significantly compensate for the shortcomings of PVT method. TSSG method is gradually becoming one of the highly competitive innovation technologies for low-cost, high-quality SiC single crystal substrate. Firstly, the basic theory of TSSG method for SiC crystals growth is introduced, and the key points of each process are given. Then the main technical advantages of TSSG method are summarized and the research status at home and abroad are reviewed. Furthermore, the key technical issues, mechanisms, and possible solutions for the growth of SiC crystals by TSSG method are discussed. Finally, the future development of TSSG method for growing SiC crystal is given.

Research Articles

Growth and Scintillation Properties of Cerium-Doped Cs₂BaBr₄ Crystal

YIN Jie, ZHANG Xiaoqiang, CHEN Can, PAN Jianguo

2024, 53(5):  760-765. 

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Using BaBr₂, CsBr, and CeBr₃ with high-purity as raw materials, the Cs₂BaBr₄∶1%Ce³⁺ polycrystalline powders were synthesized by solid-state reaction method. The crystal of Cs₂BaBr₄∶1%Ce³⁺ was grown by Bridgman method. The wafer of Cs₂BaBr₄∶1%Ce³⁺ with different thickness were obtained by incising, grinding and polishing process. The phase of the crystal was analyzed, and XRD patterns show that the crystal is a uniformly molten substance with no phase transition. The scintillation performance of the crystal was studied, which the optical transmittance, photo luminescence, X-ray induced luminescence, multi-channel gamma energy spectrum and decay time were measured. Compared with the crystal of LaBr₃, the hygroscopicity of the crystal was analyzed. The results show that the optical transmittance of crystal is close to 80%, and under the excitation of ultraviolet light and X-rays in a certain band, the crystal exhibits emission peaks at wavelengths around 349 and 372 nm. The energy resolution under the excitation of gamma rays of ¹³⁷Cs is estimated to be 11%. The decay time under the excitation of UV light is fitted to be 21.9 ns. The hygroscopicity of the crystal is much better than that of LaBr₃ crystal.

Simulation on DC Characteristics of AlN/β-Ga₂O₃ HEMT

HE Xiaomin, TANG Peizheng, ZHANG Hongwei, ZHANG Zhao, HU Jichao, LI Qun, PU Hongbin

2024, 53(5):  766-772. 

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DC characteristics of AlN/β-Ga₂O₃ high-electron-mobility-transistor (HEMT) was studied in this paper by using the device simulation software. Due to the strong polarization effect of AlN, a high concentration of two-dimensional electron gas (2DEG) is generated at the interface of AlN/β-Ga₂O₃ heterojunction, resulting in AlN/β-Ga₂O₃ heterojunction based HEMT exhibits superior device performance. Theoretical calculation shows that the surface charge density generated at the interface of AlN/β-Ga₂O₃ heterojunction is 2.75×10¹³ cm^-2. By analyzing the energy band structure and channel electron concentration distribution of the device, the effects of parameters such as AlN barrier layer thickness, gate length, gate drain spacing, and metal work function on the transfer and output characteristics of the device were studied. The following results were obtained. As the thickness of AlN barrier layer increases, the threshold voltage decreases, the maximum transconductance decreases, and the drain saturation current increases with the increase of channel electron concentration. As the gate length shortens, the transconductance increases, and the gate length shortens to 0.1 μm, the device experienced a short channel effect. And as the gate length decreases, the electron concentration in the channel area under the gate increases, while the electron velocity remains basically unchanged, resulting in an increase in drain saturation current, a decrease in conduction resistance, and a deterioration in the saturation characteristics of the device. As the distance between the gate and drain increases, the transconductance increases, and the electron concentration in the channel region remains unchanged, while the electron velocity slightly increases, resulting in an increase in saturated leakage current. An increase in the Schottky gate metal work function will increase the threshold voltage without changing the device transconductance. The decrease in channel electron concentration will lead to a decrease in drain saturation current. The above conclusions provide a theoretical basis for the optimization and improvement of subsequent devices.

Molten KOH Etching Behaviors of Heavily Doped P-Type SiC

CHENG Jiahui, YANG Lei, WANG Jinnan, GONG Chunsheng, ZHANG Zesheng, JIAN Jikang

2024, 53(5):  773-780. 

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In this paper, the dislocations in heavily doped P-type 6H-SiC crystals grown by liquid phase method have been studied in detail by melt KOH etching method. The effects of etching time and temperature on the surface etching of the heavily doped P-type 6H-SiC wafers grown by liquid phase method were investigated. The increase of etching temperature or etching time enlarge the etching pit size on the wafer surface, and the over etching happen at over temperature and long etching time. The optimal parameters for etching heavily doped P-type 6H-SiC wafers were determined according to the morphology and distribution of etching pits under different etching conditions. The reaction activation energy of the heavily doped P-type 6H-SiC crystal is calculated to be 10.59 kcal/mol through the etching rate variation relationship of the wafers at different temperatures and Arrhenius formula. Finally, the detailed characterizations on the morphologies, sizes and internal structures of threading screw dislocation (TSD) and threading edge dislocation (TED) in the wafers indicate that the inclination angle of etching pits in P-type 6H-SiC crystals is independent of the etching time.

Influence of VGF Indium Phosphide Single Crystal Furnace Heater on the Thermal Field Distribution in the Furnace

AI Jiaxin, WAN Hongping, QIAN Junbing, WEI Hua

2024, 53(5):  781-791. 

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As an important compound semiconductor, Indium phosphide (InP) is extensively utilized in the fields like communication, aerospace and artificial intelligence. The quality of InP single crystal growth depends on the stability and temperature control of the thermal field inside the growth furnace. As a widely used method in the industrial production of InP crystals, the vertical gradient freeze (VGF) method is used to construct a high-temperature, closed, stable and controllable thermal field in indium phosphide single crystal growth furnace. Due to the lack of direct observation and complete parameter monitoring methods in the furnace, the temperature field of crystal growth in the furnace is scientifically analyzed using computer numerical simulation to obtain the best growth temperature control conditions, which has become an effective and important method. This article establishes a three-dimensional physical and mathematical model of the thermal field of InP single crystal growth system based on ANSYS finite element software and measured parameters of furnace components. Based on temperature discrete data during the growth process of indium phosphide single crystal, the constructed model is compared and validated, and good agreement with actual production temperature data is obtained (temperature deviation is controlled within 3%), verifying the effectiveness of the constructed model. Based on this model, this article explores the influence of temperature fluctuations of the four stage heaters on the distribution of the thermal field under production conditions, and studies the influence of temperature fluctuations of the four stage heaters on the low-temperature zone, high-temperature zone and material pipe center temperature in the furnace. The conclusions obtained have certain guiding significance for revealing the distribution and adjustment methods of the thermal field in InP single crystal furnaces in industrial production processes.

Research on the Influence of Czochralski Process Parameters on Oxygen Content of N-Type Monocrystalline Silicon

CHAI Chen, ZHANG Jun, WANG Yulong, HAN Qinghui, LI Huaiming

2024, 53(5):  792-802. 

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TOPCon cell substrates are dominated by N-type silicon wafers, and the oxygen content of N-type silicon wafers affects the conversion efficiency of TOPCon cells to a certain extent. In this paper, the Czochralski method was used to grow monocrystalline silicon, and the influence of crystal growth process parameters on the oxygen content of N-type monocrystalline silicon were studied by adjusting the crucible rotation rates, argon flow rates and furnace pressure. The numerical simulation analysis and experimental results show that: the accretion of crucible rotation rates can suppress buoyancy-thermal capillary vortices, reduce the volatilization of SiO at the melt interface, and increase the oxygen content in the silicon melt and in the monocrystalline silicon rods; increasing the argon flow rates and decreasing the furnace pressure can enlarge the mass flow rates of SiO at the melt interface, effectively promote SiO volatilization, reduce the oxygen content at the solid-liquid interface, and thus lessen the oxygen content in the monocrystalline silicon rods. The monocrystalline silicon oxygen content test and EL detection results show that, with the 5 r/min of crucible rotation rate, 100 L/min of argon flow rate, and 1 200 Pa of furnace pressure, the oxygen content in N-type monocrystalline silicon is the lowest, and the concentric circle ratio is also the lowest in the production of photovoltaic cells. The research in this paper can provide some ideas for reducing oxygen content in N-type monocrystalline silicon rods.

First-Principles Study of Lead-Free Quaternary Thioiodides with Outstanding Optoelectronic Properties for Solar Cells

WANG Leilei, YIN Zhenhua, ZHANG Yunke, LIU Lei, CHEN Ming

2024, 53(5):  803-809. 

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Organic-inorganic hybrid halide perovskites have garnered significant attention as photovoltaic materials due to their exceptional solar cell performance and ease of fabrication. Nevertheless, their commercial viability remains hindered by poor stability and Pb-related toxicity. Quaternary thioiodides, defined by ns² lone pair cations and robust metal-chalcogen bonds, exhibit favorable properties including suitable bandgaps, high permittivity, and enhanced stability. In this study, a novel quaternary thioiodide material, Ba₂BiS₂I₃, aiming to overcome the stability and toxicity issues faced by lead-based perovskites, has been proposed. Employing first-principles calculations, it is determined that this material possesses an appropriate solar cell bandgap, high dielectric constant, low effective mass, and low exciton binding energy, showing potential as a new outstanding photovoltaic material. Moreover, our calculations indicate superior optical absorption properties for this material. Notably, the theoretical spectroscopic limit for maximal efficiency of Ba₂BiS₂I₃ exceeds 28%. This investigation establishes the potential of lead-free quaternary thioiodides in advancing photovoltaic technology.

Preparation and Characterization Study of Flexible Luminescent Solar Concentrators Based on Silicon Coated Carbon Dots

DOU Yongliang, ZHANG Yufei, NIE Cheng, REN Weijie, SONG Kai, MENG Shuai, ZHANG Rui, LI Kun, QIN Zhenxing, WANG Kaiyue

2024, 53(5):  810-817. 

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At present, the environmental problems caused by fossil fuels are becoming more prominent, and it is imperative to reduce carbon emissions. Based on this situation, the solar photovoltaic technology has become the fastest growing renewable energy technology, and it has great promise to solve current resource and environmental problems. Owing to the characteristics of adjustable structure, sustainable use, and low cost, the luminescent solar concentrators are attracting more and more attention from among photovoltaic field. The typical luminescent solar concentrator is composed of two parts, including the light waveguide coated or embedded with the emitting fluorophores, a photovoltaic cell mounted on the light waveguide edge. Carbon dots have attracted increasing attention in the field of luminescent solar concentrators due to their environmental friendliness, economic applicability, simple synthesis methods, and excellent optical properties. However, when carbon dots are compatible with hydrophilic polymer waveguide materials as luminescent substrates, the poor compatibility of most carbon dots in polymers and the brittleness of hydrophilic polymers severely limit the practical application of luminescent solar concentrators. In order to solve these problems, the synthesis of a carbon dot doped with other elements or new carbon dot structure has become the focus of attention. In addition, the suitable host matrix needs to be explored, such as organic-inorganic hybrid matrix, multifunctional matrix, polysiloxane matrix, etc. In this work, a bright yellow emitting silicon coated carbon dot with a Stokes shift of 150 nm, a quantum yield of 10.94%, and good dispersibility and compatibility was synthesized using the hydrolysis condensation of 3-aminopropyltriethoxysilane, along with phthalic acid and o-phenylenediamine. At the same time, a series of 3 cm×3 cm×0.1 cm sizes were prepared by combining dimethyl siloxane with good compatibility and high flexibility as the waveguide material, flexible luminescent solar concentrators based on silicon coated carbon dots with different mass percentages, among which the best performing solar concentrator has an energy conversion efficiency of 1.05%. This work combines the advantages of silicon coated carbon dots with polydimethylsiloxane, which has potential value for the practical application of luminescent solar concentrators.

Single-Sided Deposition of Poly-Si in TOPCon Solar Cells

DAI Tongguang, TAN Xin, SONG Zhicheng, GUO Yonggang, YUAN Yajing, NI Yufeng, WANG Liang

2024, 53(5):  818-823. 

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At present, the technology of tunnel oxide passivated contact (TOPCon) solar cells is becoming more and more mature, and the manufacturing cost is decreasing. TOPCon cell technology has been applied in the process of manufacture. Low-pressure chemical vapor deposition (LPCVD) is widely used in the industry for double-sided deposition or single-sided deposition. Single-sided deposition has the problem of Poly-Si winding coating, which seriously affects the efficiency and appearance quality of solar cells. It is difficult to remove the winding coating on the front side. While removing the winding coating in alkali solution, there is a risk of incomplete removal of the winding coating or corrosion risk of P⁺ layer in non-winding plating area. As a result, the P⁺ emitter is damaged, which seriously affects the appearance quality and performance of solar cells. Double-sided deposition can avoid the above risks, but the production capacity will be reduced by half, the manufacturing cost will increase. In this paper, the single-sided deposition of Poly-Si process and the removal process of the winding coating were studied. A layer of oxide coating with appropriate thickness is made on the front and back of TOPCon solar cells. With appropriate cleaning process and unwinding plating cleaning process, the Poly-Si winding coated with P⁺ layer can be effectively removed, and the front P⁺ layer and the doped Poly-Si layer on the back can be well protected from damage, and the production capacity can be greatly improved.

Morphology Regulation and Doping Modification on the Photocatalytic Properties of TiO₂ Catalyst

WANG Dandan, LIU Wenqiang, ZHAO Lin, LI Chao, LI Shijie

2024, 53(5):  824-832. 

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In order to improve the photocatalytic activity of TiO₂, mesoporous TiO₂, C/TiO₂, Nd/TiO₂ and C/Nd/TiO₂ were prepared by sol-gel method, and multistage ordered C/Nd/TiO₂ catalyst was prepared using polystyrene (PS) colloidal crystals as template. The properties of the prepared catalysts were analyzed by SEM, XRD, XPS, UV-Vis DRS and N₂ adsorption-desorption. The photocatalytic properties of the prepared catalyst materials for methyl orange solution were investigated under simulated visible light conditions. The results show that the surface morphology of the anatase type of multistage orderly C/Nd/TiO₂ catalyst is arranged in order, and internal is the cross linking pore structure. Macroporous structure shows the hexagonal structure to produce good openness. Larger specific surface area and pore volume provide a larger space for mass transfer. Through the synergistic effect of non-metal C and rare earth metal Nd, the band gap of multistage orderly C/Nd/TiO₂ is narrowed, which reveals good catalytic activity. As a result, the photocatalytic decolorization rate of multistage ordered C/Nd/TiO₂ catalyst is up to 81.15% at illumination 210 min.

Preparation and Luminesent Property of CaWO₄∶Eu³⁺,Bi³⁺ Red Phosphors

CAI Xiaoyong, JIANG Hongxi

2024, 53(5):  833-840. 

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A series of CaWO₄∶Eu³⁺,Bi³⁺ red phosphors were successfully synthesized by high temperature solid-state reaction. The crystal structure, microstructure, optical property, energy transfer mode, fluorescence lifetime, and thermal stability of samples were characterized by X-ray diffraction, scanning electron microscope and fluorescence spectrophotometer, etc. The results show that when the doping concentrations of Eu³⁺and Bi³⁺ are 7% and 2% (mole fraction), respectively, the red luminescence (615 nm) is the strongest. Theoretical calculations show that the size of this fluorescent powder particle is around 50.27 nm. This is consistent with the observation results of the electron microscope. The main mode of energy transfer is the interaction between electric dipoles and electric quadrupoles. The fluorescence lifetime of CaWO₄∶7%Eu³⁺,xBi³⁺ (x=0~6%) series phosphors were measured, and their fluorescence lifetimes were basically the same, all around 0.56 ms. By comparing the spectra of CaWO₄∶7%Eu³⁺,2%Bi³⁺ phosphors at different temperatures, and the corresponding chromaticity coordinates were calculated. It was found that the overall chromaticity coordinates shift to the left, and the luminescence intensity becomes weaker as the temperature increases, but overall, the thermal stability is good. The good thermal stability and bright red emission indicate that this fluorescent powder can be used as a potential commercial red fluorescent powder.

Preparation of BiOI Films with High c-axis Orientation by Chemical Vapor Deposition

XU Yuqi, LI Qingwen, ZHONG Min

2024, 53(5):  841-847. 

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Bismuth iodide oxide (BiOI) has attracted attention in the fields of photocatalysis, photovoltaics and photodetectors due to its low toxicity, tolerance to point defects, and strong light absorption ability. This article adopts the chemical vapor deposition (CVD) method, using BiI₃ powder as the evaporation source and O₂/Ar as the reaction gas, to obtain high c-axis oriented BiOI films on a soda-lime glass substrate. The growth mechanism of BiOI films was analyzed by studying the effects of evaporation source temperature and deposition time on the phase and morphology of the films. The results indicate that the BiOI films prepared by CVD method belongs to the tetragonal crystal system with a high c-axis orientation. The c-axis oriented thin film grows parallel to the substrate, the evaporation temperature and deposition time have a significant impact on the crystallization, absorption ability and traps of the BiOI films. When the evaporation temperature is 370 ℃ and the deposition time is 20 min, the BiOI film has the best crystallization and the lowest transmittance and traps.

Characterization and Analysis of Indium Tin Oxide (ITO) and Fluotin Oxide (FTO) Transparent Conductive Films

CHU Xuefeng, HUANG Linmao, ZHANG Qi, XIE Yihan, HU Xiaojun

2024, 53(5):  848-854. 

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In this paper, ITO films prepared by RF magnetron sputtering, and ITO and FTO films purchased were used as research objects. Ultraviolet-visible spectrophotometer was used to characterize the film transmittance of the samples. The results show that both ITO and FTO films exhibit good optical transmittance. Scanning electron microscope (SEM) was used to observe the surface morphology of the films, and the surface of all the films was relatively uniform. X-ray photoelectron spectroscopy (XPS) was used to characterize the elemental, composition, valence and electronic state information of the sample surface. The results show that the preparation method and annealing treatment affect the elemental composition and valence of the sample surface, and this information has a certain correlation with the electrical and optical properties of the film. The above research results provide reference for the design and performance improvement of new transparent conductive films.

Preparation of α-CaSO₄·0.5H₂O Crystals from Chlorine-Free Salt Solution at Atmospheric Pressure

LI Xueli, GUO Jingjing, HUO Tengfei, BAI Jiale, ZHANG Yantu

2024, 53(5):  855-863. 

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The effects of reaction temperature, reaction time, liquid-solid ratio, pH value and Na₂SO₄ mass fraction on the generation of α-CaSO₄·0.5H₂O were investigated using Na₂SO₄ solution as the reaction medium. The results show that α-CaSO₄·0.5H₂O crystals with an average length of 46.0 μm, an average aspect ratio of 17.23 and a homogeneous morphology are prepared under the conditions of Na₂SO₄ mass fraction of 12.5%, liquid-solid ratio of 5∶1, pH value of 7, reaction temperature of 97 ℃ and reaction time of 4 h. The method of chloride-free salt solution under atmospheric pressure overcomes the drawbacks of chloride ion corrosion of industrial equipment and environmental pollution, providing important technical support for the high value utilization of phosphogypsum.

Preparation of Highly Dispersed Nano Calcium Carbonate by Low-Temperature Carbonization Method

XING Jiabin, LI Wei, JIA Songyan, MA Yali, LI Xue, ZHENG Qiang

2024, 53(5):  864-872. 

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Highly dispersed nano calcium carbonate was prepared using limestone as raw material by low-temperature carbonization method. The nano calcium carbonate samples were characterized by XRD, SEM, TEM, etc. The effects of slurry ratio, carbonization temperature, CO₂ aeration rate, aging time, and crystal control agent on the particle size and dispersion degree of nano calcium carbonate were investigated. The process conditions for preparing nano calcium carbonate were obtained as follows: slurry ratio of 5%, carbonization temperature of 15 ℃, CO₂ aeration rate of 200 mL/min, aging time of 2 h, and ZnCl₂ as the crystal control agent. Under these conditions, cubic nano calcium carbonate with a grain size of 25~35 nm and uniform distribution was prepared. The growth mechanism of nano calcium carbonate was analyzed by Materials Studio. The results show that the (104) and (116) crystal planes of calcium carbonate were thermodynamically stable and would eventually become tenacious exposed crystal planes, which promots the generation of cubic nano calcium carbonate.

Study on the Conductive and Corrosion-Resistant Properties of Pt Coatings on Titanium Substrates

SONG Jie, LIANG Danxi, YUE Luo, XU Guizhi, HU Xiao, CHANG Liang, XU Chao

2024, 53(5):  873-881. 

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Proton exchange membrane (PEM) water electrolysers for hydrogen production boast a wide range of flexible and adjustable capabilities, including fast dynamic responses. They hold extensive potential in fields like new energy consumption and power grid peak shaving. To enhance the electrical transmission performance and minimize the contact resistance of the water electrolyser stack, this study employs magnetron sputtering technology to deposit Pt coatings on titanium felt and titanium plates. Scholarly investigation has increasingly adopted innovative methodologies like magnetron sputtering to develop advanced electrode materials. Central to this research is an in-depth examination of the effects of magnetron-sputtered Pt coatings on titanium felts and plates. The study meticulously analyzed these coatings to elucidate their microstructural characteristics, transport properties, and corrosion-resistance. Rigorous experimentation determined the optimal sputtering parameters: a 20 min plasma cleaning phase, a 10 min sputtering period, and a power input of 100 watts. These precise conditions yielded coatings with notable performance attributes. Specifically, the study highlighted a significant reduction in contact resistance for platinum-coated titanium felts, demonstrating the sputtering technique’s ability to enhance charge transfer kinetics efficiently. Analysis of the platinum particle dynamics employed SEM and EDS, revealing that increased sputtering power and duration led to larger platinum particles. However, maintaining a balance is crucial, as excessive particle enlargement may induce compressive forces between particles, causing micro-fissures that could compromise the coatings’ corrosion-resistance. In conclusion, the insights derived from this research are instrumental in improving the overall efficiency and durability of PEM electrolysis systems. By optimizing the fabrication process and understanding the relationship between deposition parameters and material characteristics, this study makes a significant contribution to advancing robust hydrogen production technologies, further supporting the integration of clean energy solutions.

Effect of K_0.5Na_0.5NbO₃ Doping on the Energy Storage Performance of 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ Ceramics

MIAO Jian, SHAO Hui, CAO Ruilong

2024, 53(5):  882-888. 

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A series of lead-free dielectric energy storage ceramics BNT-BT-KNN with a composition ratio of 0.94Bi_0.5Na_0.5TiO₃-(0.06-x)BaTiO₃-xK_0.5Na_0.5NbO₃(BNT-BT+xKNN, x=0.00~0.04) were prepared by solid state reaction method. The effect of KNN doping on the crystal structure, micro-structure, dielectric, ferroelectric properties and energy storage efficiency of BNT-BT-based ceramic was investigated. The results show that all the samples exhibit the pure perovskite structure with uniform and dense grains in the medium after sintering at 1 150 ℃. The addition of KNN further broadens the dielectric peak at T_m which resulted in better temperature stability and relaxation. With the increase of KNN dopant, the hysteresis curves (P-E curves) of the samples gradually change from “broad and fat” to “slender” and the residual polarization (P_r) of the ceramic samples decrease, thus the energy storage performance of BNT-BT ceramics are further improved. The optimal energy storage density of W_rec=0.048 J/cm³ was achieved at x=0.03 under a field strength of 2 kV/mm, which corresponds to an energy storage efficiency of η=43%, which proves that this material has a promising potential for application in energy storage capacitors.

Fabrication and Electromagnetic Wave Absorption Performance of C/C Composites Modified by SiC Nanowires

GUI Kaixuan, LUO Xiangjie, LIU Fangyu, ZHAO Xiaoyu

2024, 53(5):  889-898. 

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C/C composites have a wide range of applications in aerospace materials due to their low density, high temperature resistance and other characteristics. Improving the microwave absorbing performance of these materials through modification methods is expected to broaden their application fields. In this paper, C/C composite, SiC nanowire (SiC_nw), and SiC_nw modified C/C composite were fabricated by precursor infiltration and pyrolysis method, and chemical vapor reaction method using phenolic resin, Si, SiO₂ and catalyst ferrocene as raw materials. The microstructures and properties of C/C and SiC_nw/C/C composites were studied, and the influence of SiC_nw content to electromagnetic wave absorption performance of C/C composites was discussed. The results show that SiC_nw with core/shell structure is successfully introduced into C/C composite, and the SiC_nw/C/C composite exhibits excellent electromagnetic wave absorption performance with the increasing of SiC_nw content, and the minimum reflection loss of SiC_nw/C/C composite with 15.4% (mass fraction) SiC_nw is -38.02 dB with a thickness of 2.07 mm, significantly lower than those of other materials. This work provides a technical and theoretical basis for the preparation of high-performance carbon/ceramic composites.

Hygroscopicity and Thermal Expansion Properties of (ZrCa)_xY_2-2xW₃O₁₂ Solid Solution

WANG Xianli, FU Linjie, YU Zhanjun, CHEN Dongxia, DUAN Xiangyang

2024, 53(5):  899-903. 

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(ZrCa)_xY_2-2xW₃O₁₂(x =0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0) are developed with a simple solid state method, and characterized for crystal structure, hygroscopicity and thermal expansion by X-ray diffraction, Raman spectroscopy, thermal analysis and dilatometer. The results show that the hygrosopicity of solid solution decreases obviously, and the coefficient of thermal expansion (CTE) changes regularly after complete release of the crystal water with the increase of (ZrCa)⁶⁺ content. A near-zero thermal expansion (ZTE) is realized for (ZrCa)_0.6Y_0.8W₃O₁₂ as x=0.6, and the linear CTE (a_l) is measured to be 2.79×10^-7 K^-1(453~1 000 K).

Preparation of CoSe₂-CuSe₂NF Bifunctional Electrocatalyst and Its Performance in Water Electrolysis

WANG Zichen, CHEN Yongjun, LUO Lijie, ZHANG Xueyan

2024, 53(5):  904-912. 

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With the increasing environmental pollution and the depletion of non-renewable resources, it is very important for developing clean and renewable energy. The technology of water-splitting is an efficient and pollution-free method for producing hydrogen and oxygen, which is via two processes of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, the commercial precious metal catalyst has expensive cost and low abundance on earth. Therefore, it is very meaningful for developing the non-noble metal electrocatalysts with lower prices, high activity and stable performance. In this study, a series of nanoflower bifunctional electrocatalysts (CuSe₂-CoSe₂(1∶1)NF, CuSe₂-CoSe₂(3∶1)NF and CuSe₂-CoSe₂(1∶3)NF) were successfully prepared by hydrothermal method. The structure, morphology, elemental composition and valence state of CuSe₂-CoSe₂NF catalyst were analyzed by a series of characterizations. The result shows that the existence of synergistic between CoSe₂ and CuSe₂ in CuSe₂-CoSe₂NF bimetallic selenide catalyst can accelerate the electron transfer and enhance the water-splitting performance. In addition, the CuSe₂-CoSe₂NF catalyst with nanoflower structure has large specific surface area (808 m²/g), which can expose more active sites and further increase the electrochemical performance. Consequently, the CuSe₂-CoSe₂(1∶1)NF catalyst needs 42 and 204 mV overpotentials for HER and OER at 10 mA·cm^-2 current density in 1 mol/L KOH electrolyte. The stability could maintain 100 h. The CuSe₂-CoSe₂(1∶1)NF performance is close to that of commercial Pt/C and RuO₂.