Table of Content

15 August 2021, Volume 50 Issue 8

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Research Letter

Growth of 720 kg Large-Sized Sapphire Crystal by Modified Kyropoulos Method

KANG Sen, LU Yarong, SHI Tianhu, TENG Bin, KUAN Jun, LI Lu, HAO Wenjuan, DUAN Binbin

2021, 50(8):  1397-1401. 

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In order to further meet the current demand for large-sized and high-quality sapphire materials in the current new display technology, aerospace, aviation and other fields, this paper adopts the modified Kyropoulos method and self-developed furnace to grow large-sized, high-quality sapphire crystals weighing 720 kg. Sapphire panel with diameter of 640 mm is obtained from the sapphire, and the panel has no bubbles and low-angle grain boundaries. The quality of the upper, middle and lower parts of the crystal was detected. The results show that the dislocation density of the crystal is less than 475 cm^-2, the FWHM is less than 0.004 6°, and the transmittance in the band of 400 nm to 4 000 nm is more than 83%. It shows that the micro defects in the crystal are controlled, and the crystalline properties and optical properties of the crystal are excellent.

Research Articles

Growth and Luminescence Properties of K₂LaBr₅∶Pr Crystal

XIONG Jianhui, WANG Haoyu, YANG Chenyue, PAN Shangke, CHEN Hongbing, PAN Jianguo

2021, 50(8):  1402-1407. 

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K₂LaBr₅ polycrystalline materials with different doping concentrations of Pr³⁺ were synthesized by high-temperature solid-state method, and the K₂LaBr₅∶Pr single crystals were grown by vertical Bridgman technique, and cylindrical transparent crystals with ø12 mm×5 mm were obtained by a series of processing. The crystal belongs to the orthogonality system and the cell parameters has been determined as a=1.336 0 nm, b=0.992 7 nm, c=0.846 2 nm, Z=4, the crystal density is 3.908 g/cm³, the melting point is 607 ℃. The crystals were characterized by powder X-ray diffraction, X-ray excitation emission spectrum, photoluminescence spectrum, transmittance and so on. Under the excitation of ultraviolet light and X-ray, the K₂LaBr₅∶Pr crystal exhibits blue light (³P₁→³H₄), green light (³P₀→³H₄,³P₁→³H₅), orange light (³P₁→³H₆,³P₁→³F₂), red light (³P₀→³F₂,³P₁→³F₃), deep red light (³P₁→³F₄), purple light (³P₀→³F₄) and other visible wavelengths of light output in the wavelength range of 480 nm to 750 nm, which indicates that the crystal has excellent luminescent properties. Under X-ray excitation, a broadband 4f 5d-4f² emission transition is also observed in the range of 360 nm to 440 nm. The scintillation decay time of K₂LaBr₅∶Pr crystal is about 10 μs, which is measured by the steady-state transient fluorescence spectrophotometer, and the transmittance of the crystal in the visible range is 88% measured by the ultraviolet-visible spectrophotometer.

Analysis of Haze in Transparent MgO·nAl₂O₃ Spinel

PANG Zhenli, LI Zhen, WANG Lidi, TIAN Tingyan

2021, 50(8):  1408-1412. 

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In this paper, transparent MgO·nAl₂O₃ (n=0.98, 1, 1.1, 1.2, 1.3) spinel ceramics were prepared from high pure and ultra fine powder by hot pressing (HP) and hot isostatic press (HIP). Haze is very common in transparent ceramics, its presence greatly reduces transmittance and affects mechanical properties of ceramics. In order to obtain MgO·nAl₂O₃ spinel with high optical quality and suitable mechanical properties, the haze in spinel was measured and the haze formation was analyzed. It is found that many circular particles at the grain boundaries in the translucent Mg-rich samples with dense haze by SEM. The composition of the circular particles was measured to be n=0.41 by EDS. The second phase MgO is readily precipitated due to the extra magnesium, that will seriously reduce the grain boundary strength and affect the mechanical properties of ceramics. The residual MgO phase has different refractive index with spinel phase, which can cause serious light scattering and reduce the transmittance of the sample. The composition of the particles at the grain boundary was measured to be n=1.33 in another sample, the flexure strength of this Al-rich sample was measured is much higher than that of stoichiometric and Mg-rich samples.

First-Principles Study on Electronic Structure and Optical Properties of Sc and Ce Doped CrSi₂

YE Jianfeng, XIAO Qingquan, QIN Mingzhe, XIE Quan

2021, 50(8):  1413-1421. 

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The first-principal pseudopotential plane wave method based on density functional theory was used to calculate the geometrical structure, electronic structure, complex dielectric function, absorption coefficient and photoconductivity of Sc or Ce doped and co-doped CrSi₂, respectively. The results show that the lattice constants of CrSi₂ increase with the doping of Sc and Ce, and the values of bandgap decrease with the co-doping of Sc and Ce. The band gaps of Sc, Ce and co-doped CrSi₂ decrease to 0.245 eV, 0.232 eV and 0.198 eV, respectively. The Fermi level of doped CrSi₂ moves to the low energy region and enters the valence band. Due to the major contribution of the 3d state electrons of Sc and 4f state electrons of Ce, the single Sc or Ce doped CrSi₂ appears an impurity level below the conduction band. Sc-Ce co-doping makes CrSi₂ transform into metal, and the electrical conductivity is improved obviously. After doping, the first dielectric peak of the imaginary part of the CrSi₂ dielectric function increases and moves towards the direction of low energy, indicating that Sc or Ce doping enhances the optical transition intensity of CrSi₂ in the low energy region, and great intensity is obtained when the CrSi₂ is co-doped by Sc-Ce. The absorption edge of Sc or Ce doped CrSi₂ redshifts in the low energy direction. The intrinsic CrSi₂ hardly absorbs photons when the photon energy is greater than 21.6 eV, especially near higher photon energies at 31.3 eV. The absorption ability of Sc doped and Sc-Ce co-doped CrSi₂ increases, and the second absorption peak is formed near E=31.3 eV. The results show that doping Sc or Ce can improve the absorption of CrSi₂ to infrared and higher energy photons. The photoconductivity of CrSi₂ increases after doping in the low energy region of less than 3.91 eV. In the energy range of 20.01 eV<E<34.21 eV, the photoconductivity of intrinsic CrSi₂ is zero, but the photoconductivity of the Sc and Ce doped CrSi₂ is not zero. Doping broadens the optical response range of CrSi₂. The results provide a theoretical basis for the application and design of CrSi₂-based optoelectronic devices.

Analysis of Atomic Thermal Vibration of Bi₂O₃ Based on Rietveld Refinement Method

WANG Dandan, LIU Zepeng, Xianglian

2021, 50(8):  1422-1430. 

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Bismuth trioxide (Bi₂O₃) is an oxygen ion conductor. In order to obtain its atomic thermal vibration isotropic temperature factor, X-ray diffraction experiments were carried out on the powder crystal, and the crystal structure model was established. The RIETAN-2000 program refined the crystal structure of the obtained experimental results, and obtained the three-dimensional (3D) and two-dimensional (2D) visualization patterns of the powder crystal's iso-high electron density distribution through MEM analysis. The results show that the atomic thermal vibrational isotropic temperature factors of Bi₍₁₎, Bi₍₂₎, O₍₁₎, O₍₂₎ and O₍₃₎ are 0.004 938 nm², 0.004 174 nm², 0.007 344 nm², 0.007 462 nm², and 0.007 857 nm²,respectively. The three-dimensional and two-dimensional visualization of the electron density distribution at the same height further verifies the accuracy of the crystal structure model and the position of atoms. These parameters have a certain reference significance for studying the thermal properties of crystal materials.

Effect of GaAs Substrate Temperature on Indium Droplets Grown by Droplet Epitaxy

HUANG Zechen, JIANG Chong, LI Ershi, LI Jiawei, SONG Juan, WANG Yi, GUO Xiang, LUO Zijiang, DING Zhao

2021, 50(8):  1431-1437. 

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Indium droplets were grown on GaAs(001) substrates by droplet epitaxy method. The samples grown at different temperatures were characterized by atomic force microscope (AFM), and the surface morphology was observed. The study illustrates that indium droplets are very sensitive to the substrate temperature. The droplet density decreases with the increase of the substrate temperature, and its size increases with the increase of the substrate temperature. The physical mechanism of indium droplet formation at different substrate temperatures was analyzed, and the reason was explained. According to the relationship between the maximal cluster density and substrate temperature in nucleation theory, the functional relationship between the density of indium droplets and the substrate temperature is calculated as n_x=5.17 exp(0.69 eV/kT).

Synthesis and Spectroscopic Properties of ZrSiO₄∶Mn⁴⁺ Phosphor

ZHANG Shaobo, YANG Qiuhong, HU Juan

2021, 50(8):  1438-1443. 

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Zirconium silicate (ZrSiO₄) powders with different doping concentrations of Mn⁴⁺ were prepared by solid-state reactions. The effect on the photoluminescence properties of ZrSiO₄∶Mn⁴⁺ was studied. The structure of ZrSiO₄∶Mn⁴⁺ was analyzed by X-ray powder diffractometer (XRD). The result shows that the powder was completely synthesized at 1 400 ℃. The spectral properties of ZrSiO₄∶Mn⁴⁺ powders at different doping concentrations were studied. The best luminescence performance was obtained at 0.3%Mn⁴⁺ doping concentration. In the excitation spectrum, the peak at 363 nm is caused by the superposition of the charge transfer band of O^2--Mn⁴⁺ and the ⁴A₂-⁴T₁ energy level transition of the spin-allowed Mn⁴⁺, while the peak at 450 nm is caused by the ⁴A₂-⁴T₂ energy level transition of the Mn⁴⁺. The main emission peaking at 667 nm was due to the spin-forbidden transitions ²E-⁴A₂ of Mn⁴⁺. The other peak located at 698 nm was caused by anti-stokes vibronic sidebands associated with the excited state ²E of Mn⁴⁺. The decay curves show that the lifetime of ZrSiO₄∶0.1% Mn⁴⁺ powders is 0.204 1 ms. The results show that ZrSiO₄∶Mn⁴⁺ powders have good luminescent properties, they have the potential to be used in LED lighting industry.

Two Pb(Ⅱ)/Ag(I) Coordination Polymers Constructed by the Same Mixed Ligand and Their Fluorescence Properties

LIU Peng, CHEN Hongxia

2021, 50(8):  1444-1451. 

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The 2-(1H-imidazol-1-yl) acetic acid (Hima), 4,4'-bpy, reacts with metal ions Pb(NO₃)₂ and AgNO₃ respectively. Finally, [Pb₂(4,4'-bipy)(ima)(NO₃)₃]_n (1, 3D framework) and [Ag₄(4, 4'-bipy)₃(ima)₂(NO₃)₂(H₂O)₂]_n (2, 3D framework) coordination polymers were obtained. Based on the structural characterizations of the corresponding compounds, their chemical and physical properties, such as photoluminescence was investigated. The solid-state photoluminescence spectra of 1 and 2 at room temperature are observed to have their main emission at 552 nm and 444 nm (λ_ex=346 nm for 1, 369 nm for 2), respectively, which is mainly assigned to the ligand-metal charge transfer (LMCT).

Synthesis and Characterization of Ni(Ⅱ) Complex of 2,2'-Bipyridine-6,6'-Dicarboxylic Acid

TAN Sihui, LIU Ting, ZHONG Guoqing

2021, 50(8):  1452-1456. 

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The complex [Ni(6,6'-Hbpdc)₂]·4H₂O (1) was synthesized with 2,2'-bipyridine-6,6'-dicarboxylic acid (6,6'-H₂bpdc) and nickel acetate as main raw materials by hydrothermal method. The composition and structure were characterized by elemental analyses, X-ray powder diffraction and single crystal diffraction, FT-IR spectra, and its thermal stability was also studied. The structure analyses show that the complex 1 is triclinic with space groups of P1. The cell parameters are a=1.011 2(9) nm, b=1.084 9(9) nm, c=1.267 6(11) nm, α=112.672(2)°, β=101.025(3)° and γ=90.008(3)°. The central nickel ion is coordinated by oxygen and nitrogen atoms in the ligand to form a distorted octahedral configuration with the coordination number of six, and the complex 1 forms a three-dimensional supramolecular structure through weak hydrogen bonds between molecules. The thermal stability study shows that the thermal decomposition reaction of complex 1 in nitrogen atmosphere include dehydration and oxidation decomposition of the ligand and the final residue is NiO.

Structural Characterization of Copper (Ⅰ) Complex Based on Triphenylphosphine and Thioalcohol Mixed Ligands

YAN Li, PENG Shaochun

2021, 50(8):  1457-1463. 

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In this work, a new Cu(I) complex [CuBr(L)(PPh₃)₂]·2CH₃OH (1) was synthesized using triphenylphosphine (PPh₃) and 5-methoxybenzimidazole-2-thiol (L). The complex was characterized by single crystal X-ray diffraction, elemental analysis, thermogravimetric analysis and other various spectroscopic analyses. X-ray crystallographic analysis reveals that complex (1) crystallizes in the monoclinic system with P2₁/c space group. Each central metal ion is four-coordinated with one bromide ion, two phosphorus atoms from two PPh₃ ligands and one sulphur atom from one L ligand, resulting in a mononuclear complex. In addition, the fluorescence spectra of 1 in methanol solution and solid state show that the emission mechanism belongs to metal-to-ligand charge transfer (MLCT) based on PPh₃. The difference of the fluorescence emission maximum of 1 in the methanol solution is not shifted compared to PPh₃, while red-shifted by 6 nm compared to PPh₃ in solid state, indicating that the structure of 1 in methanol solution is different from that in solid state.

Synthesis, Structures and Properties of Tetrazole Compounds by Demko-Sharpless Method

YING Tingting, HAN Dingchong, TAN Yuhui, LI Yukong, HUANG Jun, TANG Yunzhi, DU Pengkang, ZHUANG Jiachang

2021, 50(8):  1464-1470. 

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The tetracyanopyridine (4-cyanopyridine and 3-cyanopyridine) was reacted with rare earth nitrates (Ln=La, Gd, Er) under hydrothermal conditions by the Demko-Sharpless method, and four rare earth tetrazolium ionic compound were synthesized safely and effectively, named [Ln(H₂O)₈·3(p-TPD)·2(p-HTPD)·7H₂O], (Ln=La(1), Gd(2), Er(3), p-TPD=4-tetrazolpyridine), [Ln(H₂O)₈·3(m-TPD)·6H₂O], (m-TPD=3-tetrazolpyridine, Ln=Er(4)). These four rare earth tetrazolium ionic compounds were characterized by the single crystal X-ray diffraction, infrared spectroscopy, thermogravimetry, dielectric properties, X-ray powder diffraction. The X-ray single crystal structure analysis shows that the four rare earth tetrazolium compounds were all ionic, and the rare earth metal ions and ligands were in two different layers. The [Ln(H₂O)₈]³⁺ structure unit and p-TPD and water molecules formed a cationic layer through hydrogen bonding, while p-TPD and p-HTPD formed an anion layer through π-π stacking and hydrogen bonding. The cation layer and anion layer alternately form a regular network structure. Moreover, the dielectric properties tests indicate that the compounds 1, 2 have good dielectric properties.

A Three-Dimensional Zn(Ⅱ) Metal-Organic Framework with Fluorescent Properties

ZHU Baili, HE Pengzhen, WANG Qinghua, CUI Shuxin

2021, 50(8):  1471-1477. 

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The complex {[Zn(BTC)_2/3]·[HCON(CH₃)₂]·[C₂H₅OH]}_n(1) was prepared from 1,3,5-benzenetricarboxylic acid (H₃ BTC) and Zn(Ⅱ) cation via a solvothermal technique. The complex 1 was characterized by single crystal X-ray diffraction(SXRD), Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) and fluorescence spectroscopy. Single crystal X-ray diffraction analysis indicates that complex 1 belongs to space group P2₁/n of the monoclinic system. In complex 1, the Zn(Ⅱ) ion is coordinated with BTC^3- anion through the oxygen atom on the carboxyl group, forming a three-dimensional Zn(Ⅱ) metal-organic framework (MOF) structure with channels. And through intermolecular hydrogen bond interaction, ethanol and N, N'-dimethylformamide (DMF) molecules are encapsulated into parallelogram channels. Fluorescence spectrum analysis at room temperature shows that when the excitation wavelength is 297 nm, complex 1 has the strongest emission peak at 601 nm.

Structure and Transparent Conductive Properties of (Ti/ZnO)_N Compositionally Modulated Nano Multilayer Films

NIU Ben, WU Jun, WANG Kaifeng, HUANG Chengbin, FU Hao, ZHU Bolin, LI Taotao, YAO Yagang

2021, 50(8):  1478-1484. 

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Using radio frequency (RF) and unipolar medium frequency direct-current (DC) pulsed magnetron sputtering methods, (Ti/ZnO)_N compositionally modulated nano multilayer films were prepared on the glass substrate, the effects of number of modulation cycles on the the structure and transparent conductive properties of the films were investigated. The results of X-ray diffraction, Raman spectroscopy, atomic force microscopy, ultraviolet-visible transparent spectroscopy and Hall effect show that the prepared (Ti/ZnO)_N compositionally modulated nano-multilayer films have hexagonal wurtzite structure of ZnO with preferred (002) orientation, and clear compositionally modulated nano-multilayer structure, in which the Ti and ZnO layers are flat, continuous and with uniform thickness, while the interface is clean and without diffusion. The average optical transmittance in the visible range is higher than 85% while the minimum resistivity is at about 2.63×10^-2 Ω·cm.

Preparation and Properties of MCNOs/CdS Dual-Effect Photocatalyst

ZHANG Jing, SHI Qianying, GONG Hao, GUO Yufe, ZHANG Weike

2021, 50(8):  1485-1495. 

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The MCNOs/CdS photocatalysts with different magnetic nanosized carbon (MCNOS) loads (0%, 1%, 3%, 5%) were prepared by hydrothermal synthesis. It was characterized by XRD, SEM, FT-IR, XPS, UV-Vis and VSM. The influence of MCNOs loading ratio on RhB performance and mechanism of catalyst in visible light degradation was investigated. The results show that MCNOs can effectively improve the photocatalytic effect of CdS. The degradation rate of 3%MCNOs compound is 96%, which is 30% higher than that of pure CdS. Magnetic analysis shows that it has good paramagnetism and can realize effective recovery of catalyst. The first-order reaction kinetic line of MCNOs/CdS photocatalyst degradation of RhB under visible light has a good degree of fit, indicating that the prepared catalyst has good catalytic activity.

Electrochemical Activity of Catalytic Ethanol Oxidation Properties Based on Ru@Pt/CNTs Nanoparticles

ZHANG Yujie, XIAO Fengyan, ZHAO Bin

2021, 50(8):  1496-1502. 

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Carbon nanotubes loaded by different ratios of core-shell structured ruthenium platinum nanoparticles (Ru@Pt/CNTs) were prepared by ethanol reduction methods and used as anodic catalysts for direct ethanol fuel cells. The structures of the as synthesized catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that Ru@Pt/CNTs nanoparticles formed a core-shell structure (the core was ruthenium and the shell was platinum). Meanwhile, the electrochemical measurements demonstrates Ru@Pt/CNTs exhibits ultrahigh electrochemical catalytic activity(Ru@Pt_0.75/CNTs,1 767.77 mA/mg Pt) and durability(Ru@Pt_1.0 CNTs, CV decay of 19.7% after 250 test cycles) in ethanol electro-oxidation reaction(EOR) compared with commercial Pt/C catalysts. Therefore, the Ru@Pt/CNTs nanoparticles with core-shell structure have an excellent catalytic activity for ethanol oxidation.

Synthesis and Electrochemical Performance of SnO₂/Graphite Hierarchical Nano-Heterostructure

LUAN Zhaojin, YAN Gongqin, TAN Shanghua

2021, 50(8):  1503-1510. 

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SnO₂/graphite hierarchical nano-heterostructure was synthesized by a one-step hydrothermal method using graphite as the substrate, tin tetrachloride pentahydrate as the tin source, and sodium hydroxide as the precipitant. The morphology, structure and composition of the SnO₂/graphite hierarchical nano-heterostructure were characterized by FESEM, XRD, EDS and Raman. It is found that tin dioxide nanowires with good crystallinity are firstly assembled into tin dioxide nanorods, then the tin dioxide nanorods are further assembled into flower-like structures with a diameter of 450 nm and grow uniformly on the graphite sheet, showing a hierarchical structure. The electrochemical performance of those hierarchical nano-heterostructure was tested by cyclic voltammetry and constant current charge-discharge cycle method. The results show that the initial discharge capacity and charge capacity are 1 567.2 mAh/g and 825.9 mAh/g respectively at a charge-discharge current density of 50 mA/g. The cyclic voltammetry curves of different cycles are almost the same, indicating that the SnO₂/graphite hierarchical nano-heterostructure has high storage capacity and improved cycle stability.

Effect of Vanadium Modification on the Activity and Alkali Resistance of Iron-Based de-NO_x Catalyst

LI Yue, JIANG Hong, CAI Sixiang

2021, 50(8):  1511-1517. 

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The FeV/TiO₂ catalyst was prepared by introducing V species to modify the iron-based catalyst, and the structures and performances were compared with the unmodified catalyst. The catalysts were characterized by means of XRD, Raman, BET, UV-Vis-NIR, NH₃-TPD and H₂-TPR. The results show that FeVO₄ exists as the main phase in the catalyst after introducing V, and there were abundant acid sites to guarantee strong surface acidity. The strong interaction between Fe and V species also greatly enhance the redox ability. Therefore, the low-temperature activity is significantly improved and the temperature window is greatly widened. Moreover, the structure of the catalyst is hardly affected by alkali poisoning, and the catalyst could still maintain strong surface acidity after poisoning, resulting in good resistance to alkali metals.

Preparation of Calcium Cobaltate Thin Films and High Temperature Wave-Absorbing Properties

GAO Yunfei, XU Baocai, GAO Haitao, DUAN Rongxia, MENG Na

2021, 50(8):  1518-1524. 

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Calcium cobaltate thin films were prepared by coating and sintering on alumina ceramic substrate with calcium cobaltate powder prepared by sol-gel method. The phase structure, temperature resistance characteristics and wave-absorbing properties of the thin films were studied. It is found that the calcium cobaltate powders prepared by sol-gel method are composed of Ca₉Co₁₂O₂₈ phase, and the powder particles are uniform, with a certain orientation growth and obvious lamellar structure. The sintered calcium cobaltate film is composed of fine Ca₃Co₄O₉ phase, which is closely bound to the alumina substrate. The thickness is about 20 μm. The square resistance of the films decreases rapidly with the increase of temperature, and keep around 20 Ω/□ at 300 ℃ to 800 ℃. At 800 ℃, the resistance-film type metamaterial absorber exhibits double absorption peaks at 8 GHz to 18 GHz.

Effect of Molding Pressure on Microstructure and Properties of SiC Nanofiber-Reinforced SiC Ceramic Matrix Composites

HOU Hongchen, ZHENG Xupeng, LOU Yongwei, CHENG Weiqiang, CHEN Jianjun

2021, 50(8):  1525-1533. 

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SiC nanofibers preforms with different volume fraction of nanofibers were fabricated by the different molding pressures. SiC nanofiber-toughened SiC ceramic matrix composites were prepared by the combined processes of precursor infiltration and pyrolysis with reactive melt infiltration. The effect of molding pressure on the structure and properties of SiC ceramic matrix composites was investigated. Results show that the preforms with high volume fraction of SiC nanofibers can be fabricated by compression molding. When the molding pressure is 40 MPa, the volume fraction of SiC nanofibers is 22.13%. However, there exists the fracture of SiC nanofibers if the molding pressure is too high. The porosity of the composites prepared by the combined processes of precursor infiltration and pyrolysis with reactive melt infiltration is much lower than that by the simple process of precursor infiltration and pyrolysis. The average porosity of the composite materials prepared by these two methods is 1.43% and 14.19%, respectively. When the molding pressure is 30 MPa, the composites have low content of free silicon and the long SiC nanofibers have high length-diameter ratio. Meanwhile, the corresponding value of the bending strength and fracture toughness of the composites is 178 MPa and 21.6 MPa· m^1/2, which is the largest under the different molding pressures.

Lithography-Free Interdigitated Back Contact Silicon Solar Cells with Solution-Processed PEDOT∶PSS as the Efficient Hole Transport Layer

SUN Zongheng, SHEN Rongzong, SHI Yanbin, ZHOU Yurong, ZHOU Yuqin, LIU Fengzhen

2021, 50(8):  1534-1540. 

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The I-V characteristics of the PEDOT∶PSS/metal hetero-contacts with different metals of Mg, Al and Ag were investigated. It's found that the resistivity of the Mg(Al)/PEDOT∶PSS contact is considerably high, which may play the role of an insulated layer. Based on this phenomenon, a simple lithography-free interdigitated back contact silicon solar cell using PEDOT∶PSS as the hole transport layer and LiF as the electron transport layer was designed and fabricated. During the fabrication of the solar cells, shadow mask was used only once attributed to the insulating effect of the Mg/Al/PEDOT∶PSS contact. Then a MoO_x layer grown by hot wire oxidation-sublimation deposition technique was overlaid on PEDOT∶PSS and a LiF thin film with appropriate thickness was thermal evaporated into the interface between Si and Mg/Al to improve the ability of carriers collection of the device. And the interdigitated back contact silicon solar cells with a highest VOC of 592 mV and a best efficiency of 10.13% are achieved. Using metal-assisted chemical etching to prepare silicon nanowire structure which improves the effect of front surface light trapping, an interdigitated back contact solar cell with a V_OC of 587 mV, a J_SC of 35.57 mA/cm², a FF of 69.97%, and an efficiency of 14.61% is fabricated.

Optimal Design and Analysis of Heating System of Czochralski Single Crystal Furnace

LIN Guangwei, WANG Shan, ZHANG Xiya, GAO Junwei, GAO Dedong

2021, 50(8):  1541-1551. 

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Reducing the production cost of the monocrystalline silicon battery is the key to improve the benifits of the photovoltaic industry. During the equal-diameter crystal pulling process, the sectional heating can reduce the output power of the heater and lower the energy consumption of the heating system. Based on the analysis of the heating area and energy consumption in the pulling process of monocrystalline silicon, this paper proposes to optimize the heating system of single crystal furnace via subdividing the heater structure and improving the heating circuit. Two-stage heating and three-stage heating (i.e., Scheme 1 and Scheme 2, respectively) models were designed in the experiment, and they were imported into the finite element simulation software for simulation. The results show that the two-stage heating model possesses a greater effect on the pulling process, and the three-stage heating counterpart shows a smaller effect on the pulling process, which can better ensure the stability of the pulling process. The energy consumption calculation shows that the energy consumption of the former is reduced by 6.98%, while the energy consumption of the latter is reduced by 9.49%. Therefore, three-stage heating is more conducive to reducing the production cost of photovoltaic enterprises.

Research on Identification Method of Crystal Diameter Model Based on Data Driven

ZHANG Xiya, GAO Dedong, WANG Shan, LIN Guangwei, GAO Junwei

2021, 50(8):  1552-1561. 

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Czochralski silicon single crystal growth is a dynamic time-varying process with multi-field and multi-phase coupling, complex physical changes, nonlinearity and large hysteresis. However, mechanism models based on a large number of assumptions are difficult to apply in practice. Therefore, this article is based on long-term and massive crystal growth data from the CL120-97 single crystal furnace of crystal pulling workshop, which ignores the complex crystal growth environment in the furnace, analyzes the correlation of the crystal pulling parameters that affect the crystal diameter, mines the regular information contained in the data, and further builds a crystal diameter prediction model based on the BP neural network. Aiming at the problem that the existing BP neural network model is easy to fall into the local minimum, the genetic algorithm is used to optimize the weight and threshold of the BP neural network to improve the accuracy of the crystal diameter prediction of the algorithm. The model prediction results are verified by actual crystal pulling data. The results show that the average relative percentage error of prediction is 0.095 71% for diameter prediction of 8 groups of randomly selected crystal pulling data. It is proved that the model is feasible for the prediction of crystal diameter in the equal-diameter stage.

Reviews

Research Progress on High-Purity SiC Powder for Single Crystal SiC Growth

LUO Hao, ZHANG Xuqing, YANG Deren, PI Xiaodong

2021, 50(8):  1562-1574. 

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SiC is considered as one of the more promising semiconductor materials because of its advantages such as wide band gap, high critical breakdown field strength, high thermal conductivity and high carrier saturation mobility. In recent years, physical vapor transport (PVT) method has made great breakthroughs in the preparation of large size and high quality SiC single crystal substrates, further promoting the application of SiC in the field of high voltage, high frequency and high temperature electronic devices. SiC powder is the raw material of PVT method to grow SiC single crystal. The purity of powder will directly affect the impurity content of SiC single crystal, so as to affect the electrical properties of SiC single crystal. The growth of high quality semi-insulating SiC single crystal is directly limited by the content of N element in the SiC powder. Therefore, the synthesis of high-purity SiC powder is the key to the growth of high-quality SiC single crystal by PVT method. This paper mainly introduces the synthesis methods and research status of high purity SiC powder, the advantages and disadvantages of gas-phase and solid-phase synthesis of high purity SiC powders are reviewed, and the development direction of high purity SiC powders synthesis in the future is put forward.

Research Progress on Magnetization Jump Effect of Perovskite RFeO₃ Crystals

BEN Xinwei, GAO Tian, ZHAI Haotian, ZHENG Xu

2021, 50(8):  1575-1582. 

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Perovskite rare earth orthoferrites RFeO₃ possesses abundant magnetism, which is due to the complex interaction between rare earth ions in 4f electron shell and iron ions in 3d electron shell. As an important phenomenon in RFeO₃ system, magnetization jump means that the magnetic moments of rare earth ions and iron ions in the system rotate 180° under a specific temperature and applied magnetic field, and the macroscopic performance is that the magnetization changes abruptly in the magnetocaloric curve. In this paper, two kinds of magnetization jump phenomena of different compounds RFeO₃ are discussed, the first type of magnetization transition usually has compensation points, and the coupling direction of F_R and F_Fe is unchanged, while the second type of magnetization transition is opposite, and the temperature region of the two types of magnetization transition is regulated by the external magnetic field.

Research Progress on Preparation Technology of Practical Bi-Based Superconducting Tape

ZHENG Beibei, SHAO Ling, CHEN Yingwei

2021, 50(8):  1583-1592. 

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Superconducting materials have excellent electrical and magnetic properties and have great development prospects. NbTi and Nb₃Sn are currently the two most widely used low-temperature superconducting materials, but they require liquid helium refrigeration to be used at 4.2 K ultra-low temperature, which is costly. The critical superconducting temperature of Bi-2223 is as high as 110 K, and can use liquid nitrogen for cooling, showing good practical value. Bi-2223 is a compound with a layered structure, which is often prepared into tapes, so that the layer direction is parallel to the surface of the tape to exert its best superconductivity. However, on the road to its practical application, there are still problems such as insufficient purity of Bi-2223 phase, insufficient density, poor crystal grain connectivity, insufficient tensile strength and elongation. In order to be practical, factors such as electrical performance, mechanical performance, and refrigeration technology must be both considered. This paper summarizes the preparation technology and research progress of the practical Bi-based superconducting tape. The preparation process of Bi-2223 precursor powder, the preparation process and research progress of Bi-2223 tape, the progress of the practical application of Bi-2223 superconducting tape, etc. are introduced respectively, which provide references for further in-depth research on its preparation process and practical application.

Development Status of Plasma Electrode Pockels Cell

ZHANG Jun, XIONG Qian, WU Zhenhai, LONG Jiao, ZHAO Junpu, ZHENG Jiangang, ZHANG Xiongjun, ZHENG Kuixing, WEI Xiaofeng

2021, 50(8):  1593-1601. 

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Plasma electrode Pockels cells (PEPC), used for multi-pass amplifier control, self-oscillation suppression and retro-reflected laser pulse isolation, are key components for giant high power lasers. In this paper, based on the demands in the developments of high power solid-state laser, an overview on the properties and progresses of PEPC is systematically presented. The status of PEPC developed at Laser Fusion Research Center is mainly introduced, including: one-pulse driven PEPC, small insertion-loss PEPC and repetition-rate PEPC.