JOURNAL OF SYNTHETIC CRYSTALS

Research Progress on High-k Gate Dielectrics Materials for 4H-SiC Based Power Devices

LIU Shuai, SONG Lihui, YANG Deren, PI Xiaodong

2024, 53(12): 2027-2042.

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Metal-oxide-semiconductor field effect transistor (MOSFET) as a typical device of silicon carbide insulate gate sturcture is one of the most widely applied devices for 4H-SiC. However, the low dielectric constant of gate oxide (SiO₂) and poor interface characteristics of SiO₂/4H-SiC limits further application of 4H-SiC insulated gate structures (metal-insulator-semiconductor, MIS). Therefore, the research on high-k gate dielectrics which is able to substitute or compensate for SiO₂ has attracted extensive attention. This paper reports several key areas on this issue to obtain a better understanding of potential high-k gate dielectrics. Firstly, an ideal gate dielectric materials for 4H-SiC would have large bandgap, high dielectric constant, good interface with 4H-SiC and favorable thermal stability. And the several methods are summarized to evaluate the structural, electrical and interface properties of gate dielectric materials. Furthermore, this paper assesses the current status of these dielectrics and their processing in terms of gate preparation, deposition temperature, interfacial propertiesand electrical performance, including HfO₂, Al₂O₃, AlN, Y₂O₃, CeO₂, ZrO₂, La₂O₃, Ta₂O₅, BaTiO₃, Ho₂O₃ and gate dielectric stacks composed of them. Finaly, based on an extensive survey on high-k gate dielectrics for 4H-SiC devices, a future perspective is provided with regards to gate leakage current mechanism, more efforts on varied materials and device viability in harsh environment.

Research Progress on Lu₂O₃ Based Laser Transparent Ceramics

ZHAO Wenhai, TAO Shixu, TONG Siyi, TANG Jian, ZUO Chuandong, CAO Yongge, MA Chaoyang

2024, 53(12): 2043-2058.

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Sesquioxide Lu₂O₃ has excellent thermodynamic properties, low phonon energy and strong crystal field characteristics, making it one of the excellent candidates for wideband high-power laser matrix materials in the near-infrared and mid-infrared spectra (1~3 μm), and attracting widespread attention in recent years. Since Lu₂O₃ has a melting point of up to 2 450 ℃, growing single crystal is extremely difficult, limiting its application development. However, Lu₂O₃ belongs to the cubic crystal system and is optically isotropic, making Lu₂O₃-based transparent ceramics a viable option. Compared to single crystal, transparent ceramics can be sintered at lower temperatures (60%~80% of the melting point of crystals) to prepare large-size samples, while the sintering cycle is greatly reduced and more conducive to mass production, so the preparation of Lu₂O₃-based transparent ceramics as a new type of laser material has the potential for a wider range of applications in scientific research, industrial production and daily life. In this paper, the preparation technology and properties of Lu₂O₃-based laser transparent ceramics doped with rare earth ions (Nd³⁺, Er³⁺, Yb³⁺, Tm³⁺, Ho³⁺) are reviewed.In the future, the development of half-oxide Lu₂O₃-based laser ceramics will be focused on large size, high power output, low scattering characteristics, high thermal stability, and composite structure design to promote the development of high-performance solid-state lasers.

Preparation and Spectral Properties of Er, Na:CaF₂ Transparent Ceramics

GAN Shiyan, MEI Bingchu, LI Weiwei

2024, 53(12): 2059-2065.

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Er³⁺, Na⁺ co-doped CaF₂ transparent ceramics with Er³⁺ dopant concentration of 3% and Na⁺ of 0%, 0.5%, 1.0%, 1.5% and 2.0% were fabricated by the vacuum hot pressing method with 16 mm in diameter and 3 mm in thickness. The average grain size of the obtained Er, Na:CaF₂ powders varied from 28 nm to 36 nm with the shape of sphere. The effects of Na⁺ doping on the transmittance, microstructure and spectral properties of Er³⁺:CaF₂ transparent ceramics were investigated. The transmittance of all the obtained ceramic samples is above 84% in the wavelength of 1 000 nm. The results show that after introducing Na⁺ into Er³⁺:CaF₂ transparent ceramics, charge-neutralized Er³⁺-Na⁺ structure formed which prevent Er³⁺ from clustering. The emission spectra of Er³⁺ in CaF₂ transparent ceramics at around 1.5 and 2.7 μm could be modulated by adjusting the concentration of Na⁺ and the near-infrared fluorescence lifetime at around 1.5 μm increase with the increasing of Na⁺ concentration, reaching a maximum of 56.75 ms.

Thermophysical Properties of (Sm_0.5Yb_0.5)₃TaO₇ Ceramics for Thermal Barrier Coating Applications

GUO Yi, NIU Miaomiao

2024, 53(12): 2066-2072.

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In this paper, (Sm_0.5Yb_0.5)₃TaO₇ was prepared via solid-reaction method in order to develop a novel ceramic layer material with excellent performance for thermal barrier coating and explore the influence of Yb addition on thermophysical performances of Sm₃TaO₇. Its crystal structure, microstructure, element composition, thermophysical performances and phase-stability at high temperatures were investigated. The final results indicate that the synthesized (Sm_0.5Yb_0.5)₃TaO₇ is of single pyrochlore-type lattice-structure, and compact microstructure, no element loss is found in the synthesis procedure. Owing to phonon scattering caused by doping cations, the thermal conductivity of (Sm_0.5Yb_0.5)₃TaO₇ reduces. Its thermal conductivity at high-temperature is about 1.02 W/(m· K), which is less than that of Sm₃TaO₇ (1.31 W/(m·K)) and Yb₃TaO₇ (1.14 W/(m·K)). Because of low electronegativity of Yb³⁺, its thermal expansion coefficient at 1 300 ℃ is about 9.92×10^-6 K^-1. Its thermal expansion coefficient is higher than that of Sm₃TaO₇ and lies in the same order with that of YSZ and La₂Zr₂O₇. The thermal conductivity and expansion coefficient of synthesized (Sm_0.5Yb_0.5)₃TaO₇ meet the requirements for thermal barrier coatings. This oxide also shows excellent phase-stability up to 1 300 ℃.

Study on Temperature Dependence of Light Output of GAGG:Ce Scintillation Crystal

WAN Qianyin, WANG Qiang, LIU Shuangquan, HUANG Xianchao, XIAO Xiong, SONG Baolin, JIANG Yunrui, TAO Zucai, DING Yuchong

2024, 53(12): 2073-2078.

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The light output performance of scintillation crystals can be affected by the temperature of the crystal. Gd₃(Ga, Al)₅O₁₂:Ce(GAGG:Ce) scintillation crystals are widely used in medical imaging, radiation monitoring, high-energy physics, and other fields. To study the temperature dependence of the light output of GAGG:Ce crystals, this paper designed an experiment with crystal temperature as a single variable. The full energy peak position of seven energy levels of γ-rays ranging from 121.8 keV to 1 112.1 keV was measured within the temperature range of -30 ℃ to 60 ℃. The curve of the light output of GAGG:Ce crystals changing with temperature was obtained, and the linear relationship between the light output of the crystal and temperature was analyzed. A linear function was used to fit the energy linearity of the corresponding channel positions for seven energies ranging from 121.8 keV to 1 112.1 keV at different temperatures. The determination coefficient R² of the linear fit was greater than 0.999 9, demonstrating that GAGG:Ce crystals have good energy linearity.

Effect of In-Situ Heating Treatment on the Quality and Properties of CdZnTe Crystals

WANG Kunyuan, LIANG Xiaoyan, MIN Jiahua, ZHANG Jijun

2024, 53(12): 2079-2084.

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Te inclusions are common defects in cadmium zinc telluride (CdZnTe, CZT) crystals. The objective of this study is to optimize the quality and properties of CZT crystals by improving the process parameters for growing CZT crystal by traveling heater method (THM) and designing an in-situ heating treatment to reduce the quantity and size of Te inclusions. The process parameters were optimized by considering the interactions between the crystal growth rate and temperature, the ratio of Te-rich materials and the temperature field. Based on the different solubilities of Te at different temperatures, this study selected 800 ℃ as the growth temperature and devised an in-situ heating treatment scheme comprising high-temperature dissolution and low-temperature desolvation. This scheme was designed to enhance the absorption of Te inclusions by a long annealing time at 860 ℃ and to reduce the number of large-size Te inclusions by a rapid temperature reduction. The results demonstrate that CdZnTe crystals subjected to in-situ heating treatment exhibit a notable reduction in the concentration of large-size Te inclusions, an increase in the concentration of small-size Te inclusions, a reduction in impurity defects and Te_i, and an increase in the concentration of Te²⁺_Cd. The current-voltage characterisation tests and energy spectral response tests show that the in-situ heating treated CdZnTe crystals exhibit higher resistivity and superior energy resolution.

Comparison on Three-Point-Bending Fracture Toughness of Free-Standing Diamond Thick Films from Three Directions

LUO Xiaohang, XU Guangyu, LI Lijun, ZHANG Yongkang, ZHANG Yachen, WU Haiping, AN Kang

2024, 53(12): 2085-2093.

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Three free-standing diamond films with 125 mm in diameter and thickness exceeded 1 mm were deposited using DC arc plasma jet and microwave plasma chemical vapor deposition. In order to reduce the influence of sample size on the results of fracture toughness, diamond film samples were cut into square cross-sections. Morphology and phase were characterized by SEM, XRD, Raman, CT, et al. Influences of defects and grain size on fracture toughness in three directions of growth surface, nucleation surface and edge surface were studied. The results indicate that during the growth process, many defects (including pores) are introduced into the film. Especially, on the side near the growth surface in thicker films, the size of pores reaches the micrometer level, so that affects the fracture toughness under different directional loads. Due to the smallest grain size, all diamond free-standing films have the maximum fracture toughness at growth surface, which are 7.8, 8.3, and 9.2 MPa·m^1/2, respectively. For thinner samples, the fracture toughness of edge surface cracks is between growth surface and nucleation surface. This is consistent with the relationship between grain size, indicating that fracture toughness is influenced by grain size. However, when the thickness exceeds 0.8 mm, the number of pores near the growth side will increase, resulting in the smallest fracture toughness (5.4 MPa·m^1/2) of diamond films with thicker side. This study provides guidance for selecting the direction of load application.

Efficient Polishing Process of Diamond in Oxygen-Enriched Environment and Its Material Removal Mechanism

LIU Shuaiwei, GUAN Chunlong, LU Yunxiang, YI Jian, JIANG Nan, KAZUHITO Nishimura

2024, 53(12): 2094-2103.

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Diamond is an excellent material for applications in acoustics, optics, electronics, and thermal management. However, their extremely low material removal rate results in very long processing durations. Therefore, it is essential to improve polishing efficiency while maintaining excellent polishing quality. In this study, a comparative experiment on the polishing of polycrystalline diamonds using diamond wheels under normal and oxygen-enriched environments has been conducted. It is found that the material removal rate reaches 2.29 μm/h under oxygen-enriched environment, which is over nine times the removal rate of 0.25 μm/h under normal condition, while maintaining good surface quality. The characterization results of atomic force microscopy indicate that, within a 30 μm×30 μm measurement area, the surface roughness Sa of the polished diamond under the oxygen-enriched environment could reach below 2 nm. Meanwhile, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal no significant structural damage. Furthermore, the material removal mechanism during diamond polishing was analyzed by X-ray photoelectron spectroscopy (XPS), the results indicate that the diamond during polishing undergoes a phase transition from sp³ to sp² structures under mechanical action, with the resultant phase transition layer being removed under both mechanical and oxidative effects. Additionally, it is observed that in the oxygen-enriched environment, the phase transition layer is removed more rapidly, indicating that oxidation plays a more significant role in the diamond material removal process.

Theoretical Study of the Structure, Electronic and Optical Properties of 4H-SiC under High Pressure

ZHANG Pan, PANG Guowang, YIN Wei, MA Yabin, ZHANG Junzhou, YANG Huihui, QIN Yanjun

2024, 53(12): 2104-2112.

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The crystal structure, electronic properties, and optical properties of 4H-SiC were investigated using first-principles calculations based on density functional theory (DFT) under high pressure. By analyzing the variations in relative volume, Si—C bond length, and structural energy of 4H-SiC across different pressures, it is found that the structure remains stable without any phase transitions up to 70 GPa. Beyond 70 GPa, the RS structure with metallic characteristics becomes energetically more favorable. Interestingly, as pressure increases, the semiconductor bandgap of 4H-SiC shows an unexpected widening trend. Concurrently, significant changes occur in its optical properties, including absorption characteristics, dielectric function, and refractive index, highlighting the potential of pressure to finely tune the electronic and optical properties of 4H-SiC. This study not only confirms the remarkable physical properties and application potential of 4H-SiC under extreme high pressure, but also provides a theoretical foundation for its use in high-pressure optoelectronic devices.

First-Principles Study on the Bonding Strength, Stability and Electronic Structure of La-Doped WC (0001)/Co (111) Interface

ZHANG Haoqiang, CAO Xingfei, WU Yuxin, ZHANG Duo, HOU Suoxia

2024, 53(12): 2113-2123.

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The interfacial bonding strength of WC/Co cemented carbide depends on its interfacial properties. In this paper, based on the first-principle of density functional theory, six kinds of WC(0001)/Co(111) interface models were constructed. On this basis, the influence mechanism of La doping on the weakest interface stability and the strongest interface stability model of WC(0001)/Co(111) was analyzed from the point of view of charge transfer, bonding mode and valence electron distribution. The results show that among the six interface models, the W-OT-Co interface is the weakest, with the maximum interface distance, the minimum adhesion work and the highest interface energy, and the crack tends to appear at the interface, while the C-HCP-Co interface with the strongest stability has the minimum interface distance, the maximum adhesion work and the minimum interface energy, and the crack tends to appear in the matrix. When the rare earth La replaces the Co atom in the second layer of the Co side of the W-OT-Co model and the W atom in the second layer of the WC side of the C-HCP-Co model, the distance between the two interfaces becomes smaller and the adhesion work increases, but the effect of strengthening the interface is different. After doping rare earth La, the bonding mode of W-OT-Co interface is the combination of weak ionic bond and metal bond, while the bonding mode of C-HCP-Co interface is the combination of strong covalent bond, ionic bond and metal bond, which leads to more stable interface. The optimal doping site of La on stable stacking configuration C-HCP-Co will significantly improve the interfacial bonding strength of WC/Co cemented carbide.

First Principles Study on the Schottky Modulation of ZnSe/Graphene Heterojunction by External Electric Field

WEI Lai, PANG Guowang, ZHANG Wen, ZHANG Lili, HUANG Yineng

2024, 53(12): 2124-2130.

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The stability of ZnSe/graphene heterojunction structure, interface interactions, interlayer charge transfer, Schottky contact type, and the influence of external electric field were studied in this paper by first principles plane wave ultra soft pseudo-potential method based on density functional theory. The results demonstrate that the heterojunction is easy to form because of its less lattice mismatch rate (below 5%), and its contact type is an n-type Schottky contact. When a positive electric field is applied, the Schottky contact type undergoes a transition from n-type to p-type. Conversely, when a negative electric field is applied, the Schottky barrier experiences a significant reduction and transforms from an n-type Schottky barrier contact to an Ohmic contact. The research results in this article will offer valuable theoretical insights for the design and fabrication of electronic optical devices, including field-effect transistors and photodetectors.

Theoretical Study of Energy Band Structure and Optical Properties of Ge_1-x-ySi_xSn_y Alloys

GU Yongshun, WEN Shumin

2024, 53(12): 2131-2140.

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SiGeSn alloys have high carrier mobility and long carrier lifetime, are compatible with complementary metal oxide semiconductors (CMOS), and possess unique optical properties and high thermodynamic stability. They are a type of semiconductor material with great potential for application in the field of optoelectronics. In this paper, eight models were constructed with a total atom count of 144, and Si/Sn atom ratios close to 3.7:1. Their electronic structures and optical properties were calculated by the generalized gradient approximation (GGA+U) method within density functional theory. The results indicate that GeSiSn alloys with higher concentrations of Si and Sn have relatively higher binding energies and better stability. As the concentration of Si and Sn increases, the bandgap of GeSiSn materials gradually decreases. The imaginary part of the dielectric function peak shifts towards lower energy, the static dielectric constant decreases; changes occur in the absorption spectrum peaks within the visible and near-infrared regions; reflectivity increases in the ultraviolet and above wavelength range, refractive index decreases, extinction coefficient shifts towards the ultraviolet region, and photoconductivity extends towards the ultraviolet region. By adjusting the concentration while keeping the Si/Sn atom ratio fixed, suitable optical properties can be obtained. These results provide a reference for the application of GeSiSn alloy materials in optoelectronic materials and devices.

Crystallization Metastable Zone Width and Growth Kinetic of Rubidium Chloride

XIAO Hai, ZENG Xiangdong, ZENG Ying, XIONG Guoyuan, ZHAO Shufang, ZHANG Xuening

2024, 53(12): 2141-2149.

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In order to obtain dynamics parameters for the purpose of crystallization process design and modeling of rubidium chloride, it was investigated that crystallization metastable zone width and growth kinetic of rubidium chloride. The turbidity meter was used to detect the metastable zone width of the aqueous solution system under different linear cooling in an isothermal batch cooling experimental device. And the desupersaturation of rubidium chloride solution with time was measured by adding seed crystal to supersaturated solution at a certain temperature. The metastable zone width of the system increase with the increase of saturation temperature, decrease with the increase of stirring rate, and increase with the increase of cooling rate. The nucleation order and nucleation rate constant of rubidium chloride were obtained by the self-consistent equation of metastable zone width. The nucleation order value is less than 3, indicating that it is instantaneous nucleation. The nucleation order and nucleation constant both increase with the increase of saturation temperature, indicating that the nucleation rate increased with the increase of temperature. When the amount of seed added exceeds a certain amount, the supersaturation of the solution decreases rapidly. According to the supersaturation curve, the growth kinetics of rubidium chloride crystal were calculated. And the growth exponent is about 2 in the experimental temperature range. The constant of crystal growth rate increases with the increase of crystallization temperature.

Analysis of Luminescence Performance of New Red Phosphor K₅Gd(MoO₄)₄:xSm³⁺,yEu³⁺

LI Mingming, XIONG Feibing, YANG Weibin, HU Zhengkai, BAI Xin, LI Jing, LIN Yaqing, HUANG Junxiong

2024, 53(12): 2150-2159.

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A series of K₅Gd (MoO₄)₄:xSm³⁺(x=0~0.10) and K₅Gd (MoO₄)₄:0.04Sm³⁺, yEu³⁺(y=0.03~0.15) red phosphors were synthesized by high-temperature solid-phase method in this paper. The photoluminescence spectra, fluorescence emission spectra, and fluorescence quenching performance of the phosphor were analyzed by X-ray diffraction (XRD), fluorescence excitation spectra, thermal quenching analysis system, and steady-state transient spectrometer. Results show that the samples synthesized by doping Eu³⁺and Sm³⁺into K₅Gd (MoO₄)₄ don't contain impurity phases, and the crystal structure remains unchanged. Under the excitation of 405 nm ultraviolet light, K₅Gd (MoO₄)₄:0.04Sm³⁺and K₅Gd (MoO₄)₄:0.04Sm³⁺, 0.12Eu³⁺can emit excellent red light with the CIE coordinates of (0.6088, 0.3904) and (0.637 3, 0.359 2). In the K₅Gd(MoO₄)₄:xSm³⁺(x=0~0.10) samples, as the Sm³⁺doping concentration increases, the luminescence intensity of the phosphor first increases and then decreases, the optimal doping concentration is x=0.04. In the K₅Gd(MoO₄)₄:0.04Sm³⁺,yEu³⁺(y=0.03~0.15) samples, the luminescence intensity of Eu³⁺first increases and then decreases with increasing Eu³⁺ doping concentration, and concentration quenching occur at y=0.12. When the temperature reaches 373 K, the fluorescence intensity of the K₅Gd(MoO₄)₄:0.04Sm³⁺phosphor sample is 94.69% of that at 293 K, while the fluorescence intensity of the K₅Gd(MoO₄)₄:0.04Sm³⁺, 0.12Eu³⁺phosphor sample is 76.3% of that at 293 K, indicating their good thermal stability. The color coordinate graph shows that, doping of Eu³⁺ leads to the color coordinate shifts slightly from the orange red region to the pure red region. Both K₅Gd(MoO₄)₄:xSm³⁺ and K₅Gd(MoO₄)₄:0.04Sm³⁺, yEu³⁺phosphor samples have the potential to be used as red phosphors for white light LED.

Synthesis, Characterization and Application of Copper (Ⅱ) Complexes Containing Pyridine Carboxylate

LUO Peng, JIANG Xi, LU Fengyang, ZHONG Guoqing

2024, 53(12): 2160-2166.

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Two complexes [Cu(pic)(im)(Him)]·2H₂O (1) and [Cu(2,6-pda)(2-Hmim)(H₂O)₂](2-Hmim) (2) were synthesized using 2-pyridine carboxylic acid and (2-Hpic) pyridine-2,6-dicarboxylic acid (2, 6-H₂pda) as main ligand, imidazole or 2-methylimidazole as auxiliary ligand. The complexes were characterized by elemental analysis, X-ray powder diffraction, infrared spectroscopy and thermogravimetric analysis. Nano-copper oxide was prepared with the copper(Ⅱ) complexes as precursors and their photocatalytic degradation of methylene blue (MB) was investigated. The experimental results show that the copper oxide can effectively degrade MB dye and has good stability. In addition, the antibacterial properties of the copper(Ⅱ) complexes were studied, and it is found that they have certain antibacterial effects on both Gram-positive and Gram-negative bacteria. In particular, the inhibition zone diameter of the complex 1 against E. coli reaches 16 mm, and the complexes show high drug sensitivity to Gram-negative bacteria.

Synthesis, Structure Characterization and Properties of Nickel (Ⅱ) MOF-Based Electrocatalyst Based on Mixed Ligands

PAN Huibin, QIAO Decong, WANG Jiaxin, GAO Xia, LU Jiufu

2024, 53(12): 2167-2172.

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Under solvothermal conditions, using Ni(NO₃)₂·6H₂O as the metal source, pentamethy lisophthalic acid (H₂MIP) ligand and 1,3-bis(2-methyl-1H-imidazol-1-yl)propane (BMIP) as mixed ligands, a new Ni(Ⅱ) organic framework material, {[Ni₄(MIP)₄(BMIP)₃]·DMF}_n (SNUT-36), was constructed. X-ray single crystal diffraction analysis shows that SNUT-36 presents a binodal (4,6) connected double-interpenetrated three-dimensional skeleton structure with topological analysis data of (3²·4⁵·5·6⁷)(3⁴·4⁷·5·6³). The obtained complex was further characterized by powder X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and other means. In addition, the electrochemical test results show that SNUT-36 achieve an overpotential of 430 mV at 20 mA·cm^-2, indicating its good electrocatalytic performance. The Tafel slope of 89 mV·dec^-1 also confirmed its good effect on improving the oxygen evolution reaction rate.

Effect of Electrostatic Field on the Preparation of TiO₂ Thin Films by Ultrasonic Atomised Pyrolytic Spraying

LI Dongmei, ZHOU Jun, WU Feifan, LYU Jiabo, XIAO Li, GONG Hengxiang

2024, 53(12): 2173-2180.

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Based on the independent ultrasonic atomised pyrolytic spraying device, an electrostatic field coupling is carried out by applying non-uniform electric field between the upper and lower walls of the reactive deposition chamber. Then, the effect of applied DC voltage on the structure and properties of the sprayed TiO₂ thin film was conducted. Upon the action of the electric field, the droplet particles are polarized and gain momentum perpendicular to the substrate surface. The Coulomb force produced by electric field cancels the influence of the thermophoresis force, and then improves the adhesion efficiency of titanium precursor on the near surface of the substrate. Thus, the crystallization property and film formation uniformity of the film is greatly enhanced. The results show that when the applied voltage is 1.0 kV, the anatase TiO₂ thin film is optimized. Its (101) crystal plane has a full width at half maximum of 0.29°, an average grain size of 94.19 nm, an average visible light transmittance of 85% and a surface roughness of 16.70 nm. By applying electrostatic fields, the momentum of incident particles near the surface of the substrate is regulated and a stable environment more conducive to the growth of TiO₂ thin film is constructed. This work provides a reference for the optimization of TiO₂ thin film preparation process.

Preparation of Multi-Morphology TiO₂ and Its Photocatalytic Degradation of Tetracycline

LI Xia, YAO Mengqin, LIU Fei

2024, 53(12): 2181-2188.

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Photocatalysis is an essential approach for treating tetracycline (TC) contaminants, and photocatalytic materials play a crucial role in this process. TiO₂ is a widely used photocatalyst, its morphology will significantly affect its catalytic performance. Therefore, urchin-like (TiO₂-U), nanoparticle (TiO₂-N) and hollow tubular (TiO₂-T) TiO₂ were prepared by hydrothermal method in this paper. The morphology and structure of the prepared catalysts were analyzed by XRD, SEM, XPS, UV-Vis DRS, N₂ adsorption-desorption and EPR, and their degradation performance of TC were investigated. The results show that TiO₂-U contains the greatest number of defects, and the synergistic effect of cationic and anionic defects narrow the band gap of TiO₂-U, which reveal the best catalytic activity. The degradation rate of TC by TiO₂-U can reach 100% at illumination 60 min. In addition, TiO₂-U has a large specific surface area due to its distinctive urchin-like structure, which is conducive to the adsorption of TC and enhances the degradation efficiency.

Controllable Synthesis of One-Dimensional Selenium Nanomaterials

YUAN Xiaohan, ZHANG Jianhua

2024, 53(12): 2189-2196.

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One-dimensional selenium nanomaterials have shown attractive prospects in the field of nanoelectronic devices due to their unique structure and physical and chemical properties. Therefore, it is of great significance to seek a fast, simple and environmentally friendly method to synthesize one-dimensional selenium nanomaterials. In this paper, with sodium selenosulfate (Na₂SeSO₃) as the selenium source and polyoxyethylene lauryl ether as the surfactant, the amorphous red selenium (α-Se) was obtained by the disproportionation reaction of sodium selenosulfate firstly, and then the amorphous selenium was converted into one-dimensional nanostructures (nanotubes or nanorods) of trigonal selenium (t-Se) under ultrasonic irradiation. The experimental results show that both the amount of acetic acid and surfactant are the key factor affecting the morphology and particle size of selenium nanotubes and nanorods. When the concentration of acetic acid exceeds 5.0 mg/mL, the product is selenium nanorods. When the concentration of acetic acid is kept at a low concentration, the product is selenium nanotubes, and the wall thickness of selenium nanotubes increases as increasing the concentration of polyoxyethylene lauryl ether. The transformation of α-Se into one-dimensional t-Se nanostructures follows the 'solid-solution-solid' growth mechanism, and the surfactant-directed growth mechanism plays an important role in the formation of nanotubes.

Effect of Deposition Temperature on the Property of Solid Oxide Fuel Cell GDC Barrier Layer Prepared by Metal-Organic Chemical Vapor Deposition

MA Chao, XIONG Chunyan, XU Yuanlai, ZHAO Pei

2024, 53(12): 2197-2204.

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The compact Gd-doped ceria (GDC) film can be applied to the barrier layer between the cathode LSCF and the electrolyte YSZ of solid oxide fuel cell (SOFC) to prevent the formation of the insulating phase SrZrO₃, thereby improving the fuel cell durability. In this paper, four (2,2,6,6-tetramethyl-3, 5-heptadione) cerium (Ce(DPM)₄) and three (2,2,6,6-tetramethyl-3, 5-heptadione) gadolinium (Gd(DPM)₃) were used as precursor, GDC barrier films were prepared on YSZ ceramic substrates using intelligent chemical vapor deposition equipment at 723~923 K. Effects of deposition temperatures on the phase composition, preferred orientation, macroscopic surface, microstructure and electrochemical properties of GDC barrier films were investigated, respectively. Light yellow GDC films with (200) preferred orientation are obtained at 748~923 K, and the GDC grains show an island growth pattern. A (200) preferred orientation light yellow GDC film with the best blocking ability is prepared at 873 K. The measured impedance of the LSCF/GDC/YSZ/GDC/LSCF fuel cell at 1 073 K is 0.08 Ω·cm², and the activation energy is 1.52 eV, indicating that 873 K is the best deposition temperature for GDC barrier film preparation using chemical vapor deposition.

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