Table of Content

15 April 2022, Volume 51 Issue 4

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Research Articles

Experimental Study on Internal Bias Electric Field of Nominally Undoped and Doped Lithium Niobate Crystals

WU Jing, LI Qinglian, ZHANG Zhongzheng, YANG Jinfeng, HAO Yongxin, LI Jiaxin, LIU Shiguo, ZHANG Ling, SUN Jun

2022, 51(4):  571-578. 

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Internal bias electric field in the lithium niobate (LN) crystal has a direct impact to the ferroelectric, electro-optic, and nonlinear effects of the crystal and the associated applications. A method to measure this field was proposed, and such a measurement in congruent lithium niobate (CLN) crystals, near-stoichiometric lithium niobate (nSLN) crystals, and doped LN crystals was performed. The results show that the internal bias electric field in the CLN crystal (reaching 2.53 kV/mm) is the largest among the three cases. Compared with the CLN crystal, this field greatly reduces in the nSLN crystals, and can be even lower by two orders of magnitudes for those grown by the lithium-rich melts method followed by vapor transport equilibration (VTE) treatment. In the doped LN crystals, the internal bias electric fields for the cases of 6.5% (mole fraction) Mg and 7% (mole fraction) Zn doping are 4 and 6 times smaller than that in the CLN crystal, respectively. The reason for causing the difference in the two doped cases was briefly discussed.

Electromechanical Properties of Ferroelectric Single Crystal PIN-PT with High Curie Temperature

LIU Manman, WANG Yuequn, XIONG Junjie, ZHANG Wenjie, KONG Shuyan, YANG Xiaoming, WANG Zujian, LONG Xifa, HE Chao

2022, 51(4):  579-586. 

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Relaxor ferroelectric single crystal Pb(In_1/2Nb_1/2)O₃-PbTiO₃ (PIN-PT) has a higher Curie temperature than Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT), which has a prospect in the application of sensors and transducers requiring high stability and high performance. In this work, the full matrix mechanical and electrical properties of [001]-poled 0.66PIN-0.34PT ferroelectric single crystal were studied by resonance method. The rhombohedral-tetragonal transformation temperature (T_RT) and Curie temperature (T_C) of 0.66PIN-0.34PT single crystal are 160 ℃ and 260 ℃, respectively. The room temperature piezoelectric coefficients d₃₃, d₃₁ and d₁₅ of 0.66PIN-0.34PT ferroelectric single crystal are 1 340 pC/N, -780 pC/N and 321 pC/N, respectively. The dielectric constants ε^T₃₃, ε^S₃₃, ε^T₁₁, ε^S₁₁ are 2 700, 905, 2 210, 1 927, respectively. The electromechanical coupling coefficients k₃₃, k₃₁, k₁₅, k_t are 87%, 58%, 38%, 61%, respectively. The value of piezoelectric constant (d₃₃) and electromechanical coupling coefficient (k₃₃) of 0.66PIN-0.34PT single crystal are smaller than those of PMN-PT single crystal, but the transverse piezoelectric properties (d₃₁) and shear piezoelectric properties (d₁₅) are slightly higher than those of PMN-PT single crystal. In addition, the trend of variation in electromechanical coupling performance was studied, and it is found that 0.66PIN-0.34PT single crystal has good temperature stability below 150 ℃.

Growth of P-Doped Diamond Large Single Crystals Along (111) Surface with Fe₃P as Additive

NIE Yuan, XU Antao, LI Shangsheng, HU Meihua, ZHAO Faqing, ZHAO Guiping, HUANG Guofeng, LI Zhanchang, ZHOU Zhenxiang, WANG Mengzhao, CHEN Jiaxi, ZHOU Xubiao

2022, 51(4):  587-593. 

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Doping is an important means to control the properties of diamond. In this paper, the P-doped diamond large single crystals were synthesized by temperature gradient method at 5.6 GPa and 1 312 ℃ using Fe₃P as the phosphorus source. The results of the optical micrographs of diamond samples show that as the amount of Fe₃P additve increases, the color of diamond crystals becomes darker, the number of inclusions increases in the crystals, and the crystal shape transforms from plate to tower, even to skeletal. It indicates that the V-shaped growth region shifts to the right when Fe₃P is added. This is due to Fe₃P has effect on the properties of the catalyst. IR spectra of P-doped diamond reveal that the concentrations of nitrogen impurity in the diamond crystals increases with the increase of the Fe₃P content. It indicates that the entry of phosphorus induces nitrogen atoms to enter the diamond lattice more easily. Raman spectra results show that with the increase of Fe₃P content, the Raman peak positions of the synthesized diamond change little, but the FWHM becomes larger. This suggests that the entry of phosphorus increases the crystal lattice distortion of diamond. XPS test results show that with the increase of Fe₃P, the content of P relative to C in diamond crystal also increases. It means that phosphorus are present in the diamond crystals synthesized by Fe₃P addition.

Influence of Fit Parameters on Driving System of Single Crystal Furnace

HUANG Ming, WANG Wei

2022, 51(4):  594-599. 

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With the development of photovoltaic industry, the demand for silicon materials increases, and the competition in monocrystalline silicon manufacturing is becoming increasingly fierce. To improve efficiency and reduce cost, single crystal furnace operating under a driving system with high stability and reliability is of importance. This paper aims to design and optimize the driving system of the single crystal furnace. The driving system of NVT-HG2000-V1 silicon single crystal growth furnace was taken as the research object. The virtual assembly with SolidWorks 3D modeling was realized, and its dynamic simulation model with ADAMS was established. Then the motion process of the driving system was simulated. Using single variable method, the influence of the fit clearance between copper sleeve and lifting shaft as well as the screw parameters on the driving force and torque was quantitatively analyzed. The results show that when the fit clearance between copper sleeve and lifting shaft reaches 0.071 mm, the driving torque required for the operation of the driving system can effectively reduces. The increase of lead screw inclination, thread pitch and friction coefficient between threads will lead to a significant increase in the torque required for the operation of the driving system. Reasonable technical suggestions have been proposed based on the research.

Stress Variation Trend and Luminescent Properties of Eu³⁺ Doped β-Ga₂O₃ Single Crystals by Ion Implantation

WANG Dan, WANG Xiaodan, XIA Changtai, SAI Qinglin, ZENG Xionghui

2022, 51(4):  600-605. 

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β-Ga₂O₃:Eu³⁺ samples with different fluence were prepared by ion implantation method and then annealed in air where Eu³⁺ optical activation was successfully achieved. The stress variation trend of β-Ga₂O₃ single crystals with Eu³⁺ fluence was characterized by Raman spectra and X-ray diffraction. It was found that with the increase of Eu³⁺ fluence, the crystal lattice stress increases first and then decreases, and its internal mechanism was analyzed. The luminescence properties of Eu³⁺ were characterized by cathodoluminescence spectra. The wide defect luminescence peak near 380 nm and the characteristic luminescence peaks of Eu³⁺ near 591 nm, 597 nm and 613 nm were observed. By Gaussian fitting, the 380 nm luminescence peak could be divided into three peaks located at about 360 nm, 398 nm and 442 nm, which are related to the self-trapping excitons and donor-acceptor pairs, respectively. In addition, the position and intensity of Eu³⁺ luminescence peaks were affected by the localized crystal field of the host.

Preparation Process of n-Type GaAs Ohmic Contact Electrode

ZUO Fen, ZHAI Zhangyin

2022, 51(4):  606-610. 

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At present, the preparation method of the n-type GaAs ohmic contact electrode is mainly based on the evaporation method. However, this method has the disadvantages of high equipment price and waste of electrode materials. Ohmic contact electrode AuGeNi/Au of n-type GaAs was prepared by ion sputtering. By optimizing the preparation process, the electrode layer with smooth surface, uniform composition and no segregation can be obtained. After annealing at 400 ℃ in argon atmosphere, the Schottky contact between the electrode and GaAs changes to ohmic contact, and the resistance between two electrodes decreases to 1/20 of the original. Choosing the appropriate annealing temperature (400 ℃ to 500 ℃), a small contact resistivity (10^-6 Ω·cm²) can be obtained, which can improve the stability of the device and reduce energy consumption. The contact resistivity is higher when the annealing temperature is lower than 400 ℃ or higher than 500 ℃, which is related to the fact that the ohmic contact has not yet formed and the “spheroidization” of Au-Ge alloy, respectively. The preparation method and process have the advantages of low equipment cost, simple process, saving electrode materials, good economic benefits and practical value, and are suitable for scientific research laboratories.

Controllable Preparation and Characterization of SnS_xSe_2-x Single Crystal Nanosheets

ZHANG Guoxin, NING Bo, ZHAO Yang, LIU Shaoxiang, SHI Xuan, ZHAO Hongquan

2022, 51(4):  611-619. 

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The band gap and carrier concentration of ternary tin dichalcogenides can be continuously controlled by changing the sulfur and selenium contents, which has large application potential in electric and photoelectric devices. In this paper, SnS_xSe_2-x (x=0, 0.2, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0) single crystal nanosheets were controllably prepared by chemical vapor deposition (CVD) technique. The prepared SnS_xSe_2-x nanosheets were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. The results prove the controllable preparation of SnS_xSe_2-x nanosheets with adjustable elemental percentages in high monocrystalline quality. The elemental percentage dependence of the Raman spectroscopy from SnS_xSe_2-x nanosheets were especially studied, and the experimental results are well consistent to the simulation results by first-principles calculation based on the density functional theory. This study provides a reliable method for the preparation of ternary SnS_xSe_2-x single crystal nanosheets with adjustable elemental percentages. A definite and nondestructive method for the characterization of ternary tin dichalcogenides is also proposed.

Electronic Structure Properties of Graphene and Graphene/Boron Nitride

QI Yue, WANG Junqiang, ZHU Zehua, WU Chenyang, LI Mengwei

2022, 51(4):  620-627. 

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Graphene grown by chemical vapor deposition has excellent mechanical, thermal and electrical properties, and has become the preferred material for a new generation of nanodevices. Theoretical research on the electronic properties of graphene will prompt the development and application of nanodevices. Based on the combination of density functional theory and non-equilibrium Green's function, the electronic structure characteristics of graphene and graphene/boron nitride with AA vertical stack structures were studied systematically in this paper. The results show that the band gap is zero at the high symmetry K point. In the range of 50 K to 400 K, the mobility of graphene decreases significantly with increasing temperature due to the electron-phonon interaction on Fermi surface. In addition, the characteristic analysis of energy band structures,density of states and electron density of graphene/boron nitride with different interlamellar space indicates that with the increase of layer spacing, the energy band gap decreases, and the energy difference between the conduction band and the valence band decreases. And increasing the number of atoms, the regularity of the change of the band gap opening between supercell and protocell structure of graphene/boron nitride is consistent, this can serve an guideline for the structural design of graphene-based devices.

Theoretical Study on Schottky Interfacial Charge and Schottky Regulation of ZnO/Graphene by Doping of Nonmetallic Elements (F, S, Se, Te)

PANG Guowang, LIU Chenxi, PAN Duoqiao, SHI Leiqian, ZHANG Lili, LEI Bocheng, ZHAO Xucai, HUANG Yineng, TANG Zhe

2022, 51(4):  628-636. 

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In this paper, the effects of F, S, Se and Te doping on the interfacial interaction and electronic structure of ZnO/graphene heterojunctions were systematically studied based on first-principles. The results show that the ZnO/graphene heterojunction layers are bonded by van der Waals force to form a stable heterojunction and an n-type Schottky barrier. The differential charge density diagram shows that the electrons of the graphene layer transfer to the ZnO layer, making the surface of the graphene layer positively charged and the surface of the ZnO layer negatively charged, forming a built-in electric field at the interface. When F atoms are added, the heterojunction presents ohmic contact. When S, Se and Te atoms are added, the contact types of the heterojunction Schottky change from n type to p type, and the height of the Schottky barrier effectively reduces, especially after Te atom is added, the height of the p type Schottky barrier reduces to 0.48 eV, which improves the electron injection efficiency. The research results of this paper will provide reference for the design and manufacture of related FET.

c-Axis-Oriented BiI₃ Thin Films Prepared by Vapor Transport Deposition

YUAN Wenbin, ZHONG Min

2022, 51(4):  637-642. 

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Bismuth based halide materials show great potential because of their non-toxic and excellent photoelectric properties. As a layered heavy metal semiconductor, BiI₃ has been used in X-ray detection, γ-ray detection and pressure sensor. Recently it attracted much attention as an absorbing material for thin film solar cells. In this paper, a simple vapor transport deposition (VTD) method is used to obtain high-quality BiI₃ films with preferred c-axis orientation on glass substrate using BiI₃ crystal powder as evaporation source. By studying the effects of evaporation source temperature and deposition distance on the phase and morphology of BiI₃ thin films, the mechanism of preferential growth of BiI₃ thin films was proposed. The results show that the BiI₃ thin film prepared by VTD method belongs to triclinic crystal system, and its optical band gap is ~1.8 eV. The deposition temperature has a great influence on the preferred orientation of the films. When the deposition temperature is lower than 270 ℃, the deposited thin films have the characteristics of preferred orientation growth along the c-axis. Beyond this temperature, the c-axis preferential orientation is not observed. When the substrate temperature is 250 ℃ and the deposition distance is 15 cm, the thin films have the highest crystallanity and octahedral morphology.

First-Principles Study of Y-Doped WS₂ Two-Dimensional Materials

NING Bo, ZHANG Guoxin, YAN Bin, ZHAO Yang, SHI Xuan, ZHAO Hongquan

2022, 51(4):  643-651. 

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WS₂ has attracted extensive attention due to its excellent physical and photoelectric properties. Based on the first-principle calculation method, electronic structure and optical properties of the intrinsic monolayer WS₂ and the Y doped WS₂ with different concentration of Y atoms substitutionally doped in W atom-site were investigated. The results show that the intrinsic monolayer WS₂ is a direct band gap semiconductor with 1.814 eV of band gap. After 4% concentration (atomic fraction) of Y doping, the band gap reduces to 1.508 eV, and the direct band gap characteristics are still maintained. As the doping concentration increases, the band gap of the doped WS₂ further decreases. When the concentration reaches 25%, the band structure transforms into indirect with the band gap of 0.658 eV, and the doped WS₂ exhibits magnetic properties. Appropriate concentration of doping can improve the conductivity of materials. As the doping concentration increases, the doped system maintains transparency, and the absorption efficiency in infrared and visible region together with the dielectric properties of the material significantly improve. This work provides a theoretical basis for the research of two-dimensional WS₂ related optoelectronic devices.

Effect of Warpage on Electronic Structure and Optical Properties of Germanene

XIONG Qihang, CEN Weifu, LYU Lin, YANG Yinye

2022, 51(4):  652-659. 

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In this paper, the first-principles method based on density functional theory was used to study the electronic structure and optical properties of germanene at different warpage, and the influence of warpage on electronic structure and optical properties was analyzed. Six different approximation methods were used to optimize the geometric structure of germanene, and the most stable structure system was obtained. On this basis, different warping structures were selected, and the stability of warping degree was demonstrated, and three stable warping structures were obtained. The band gap of germanene is opened by adjusting the warping degree, and the conversion between indirect band gap and direct band gap is realized by adjusting the warpage. The regulation mechanism of band structure and the effect of warpage on the optical properties of germanene are explained by analyzing the density of states. The results show that the warpage can effectively regulate the electronic structure and optical properties of germanene, and improve the photoelectron utilization efficiency.

Effect of Argon Annealing Time on Properties of Fe(Se,Te) Thin Films

LUO Lulin, ZHANG Jie, YANG Xinsheng, ZHAO Yong

2022, 51(4):  660-665. 

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As one of the iron-based superconducting thin films, Fe(Se,Te) thin films have the simplest crystal structure, fewer elements and easy to be synthesized, which is conducive to the study of superconductivity mechanism and has potential technical applications. In this paper, Fe(Se,Te) thin films were prepared by magnetron sputtering on CaF₂ single crystal substrates at 320 ℃ and annealed in argon atmosphere. The effects of annealing time on the crystal structure, surface morphology, composition and electrical transport characteristics of Fe(Se,Te) thin films were investigated. The results show that the crystallinity of Fe(Se,Te) thin films is good, annealing is helpful to eliminate FeSe phase in the thin films, lattice constant c is not sensitive to annealing, and the grain size of the thin films increases after annealing. The composition of Fe(Se,Te) thin films is different from the nominal composition of target material, and the longer the annealing time, the denser the particles on the Fe(Se,Te) films surface. The resistance of Fe(Se,Te) thin films decreases with the increase of temperature, showing semiconductor characteristics, and the resistance increases obviously after 3 h annealing.

Mechanism of Phase Change Temperature of VO₂ Thin Films by Doping Germanium

CUI Jinghe, JIANG Quanwei, GAO Mangmang, LIANG Sen

2022, 51(4):  666-672. 

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As a new type of reversible phase change material, vanadium dioxide (VO₂) has shown great potential in development with the regulation of its phase change temperature (T_MIT) and were extensively studied. The experiment in this study focuses on exploring the effect of germanium ions on T_MIT of VO₂ thin films and trying to explain the internal mechanism. A series of VO₂ films containing different ratios of germanium ions were deposited on polished alumina sheets. The characterization results show that germanium ions contribute to increasing T_MIT (maximum T_MIT is 84.7 ℃). The main reason for this increase is that germanium ion enhances the stability of monoclinic V-V dimer by increasing the stability of monoclinic V-V dimer, which makes the transition from low-temperature monoclinic state to tetragonal rutile state more difficult.

Preparation of Silver Modified Mixed Crystal TiO₂ by Hydrothermal Method and Its Photocatalytic Performance

ZHU Li, XIA Yangwen, HE Lili, ZHU Xiaodong

2022, 51(4):  673-678. 

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The three-phase mixed crystal TiO₂of anatase, rutile and brookite was prepared by hydrothermal method, and modified with Ag. The crystal structure, morphology and optical property of samples were investigated by XRD, SEM, TEM, PL and DRS. The results show that the prepared TiO₂ exhibits a three-phase mixed crystal structure of anatase/rutile/brookite. After Ag modification, the content of rutile increases, and the content of anatase and brookite decrease. Ag element exists in the form of elemental Ag and AgCl. Ag@TiO₂ heterostructure is more favorable to the transfer of photoinduced charges and improves the photocatalytic activity. After illumination 90 min, the degradation rate of tetracycline hydrochloride (TC) by Ag modified TiO₂ increases from 78.5% to 91.6%.

Luminescence Regulation of Blue Phosphor Sr₃LnM(PO₄)₃F:Eu²⁺

WANG Weihao, WANG Yanhui, YE Kaiwen, HU Yifan

2022, 51(4):  679-686. 

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A series of Eu²⁺ -activated Sr₃LnM(PO₄)₃F(Ln=Gd, La, Y; M=Na, K) phosphors were synthesized by high-temperature solid-phase method. The phase structure, morphology and luminescence characteristics of the samples were characterized by X-ray diffraction, scanning electron microscopy, fluorescence spectroscopy and other test methods. The experimental results demonstrate that the phosphor Sr₃LnM(PO₄)₃F:Eu²⁺ was successfully synthesized, and the particle size of the sample ranges from 2 μm to 10 μm. The phosphor has strong emission in the blue-light region, which is attributed to the 4f⁶5d→4f⁷ transition of the luminescent center Eu²⁺. The emitting color of Eu²⁺ changes from light blue to dark blue and the color purity increases after the transformation of Na to K, which effectively regulates the luminescence of Eu²⁺ in fluorapatite Sr₃LnM(PO₄)₃F. A new strategy by substituting of the secondary layer coordination atom is found to regulate the phosphors color of Eu²⁺.

Numerical Simulation of Carrier Transmission in Dye-Sensitized Solar Cells

CHENG Youliang, JI Xinfeng, LIU Meng

2022, 51(4):  687-694. 

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There are some adverse reactions in dye-sensitized solar cells (DSSC), such as dye relaxation, electrons in semiconductor films react with oxidized dye molecules and electron recombination with oxidized ions in electrolyte. It is very important to use a more sophisticated DSSC carrier transport model to simulate the photoelectric performance of the battery. Therefore, this paper is based on the carrier transport model including electron, dye cation, iodide and triiodide in DSSC established by multiple capture theory. The J-V curves of DSSC with different TiO₂ film thickness, different incident light intensity and different dye molecular absorption coefficient were obtained by numerical simulation. The results show that with the increase of TiO₂ film thickness, the short-circuit current density of solar cells increases, the open circuit voltage decreases, and the photoelectric conversion efficiency first increases and then decreases. When the TiO₂ film thickness of DSSC is 20 μm, the photoelectric conversion efficiency reaches the maximum value of 7.41%. At the same time, the photoelectric conversion efficiency increases with the increase of incident light intensity and dye molecular absorption coefficient. When the absorption coefficient is 4 500 cm^-1, the photoelectric conversion efficiency is 6.73%. The above analysis and research results can provide theoretical guidance for improving the photoelectric performance of DSSC.

Effect of LiZr₂(PO₄)₃ Coating on the Structure and Electrochemical Properties of High Nickel Ternary Cathode Materials

LIU Linlin, LIU Jie, CHEN Qianlin, LUO Shijian, LI Cuiqin

2022, 51(4):  695-703. 

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The nickel-rich ternary cathode material LiNi_0.8Co_0.1Mn_0.1O₂(NCM811) has excellent discharge capacity, which is the favorite to succeed as the next new cathode materials for lithium-ion batteries. However, it has problems such as serious Li⁺/Ni²⁺ mixed discharge, and rapid capacity fading caused by poor structural stability. In order to solve these problems, accelerate the application process of ternary cathode materials in new energy vehicle. LiNi_0.8Co_0.1Mn_0.1O₂(NCM811) ternary cathode material coated with LiZr₂(PO₄)₃(LZPO) was obtained by wet coating method, and the structure and electrochemical performance of LZPO coating on NCM811 ternary cathode material were studied in this paper. The results show that the NCM811 coated with 1%LZPO possess the most stable structure, and the best electrochemical performance. The first cycle discharge capacity at 0.1 C rate is 210.16 mAh/g, which is much higher than that of the pristine NCM811 material (201.01 mAh/g); the capacity retention rate after 200 cycles is 79.4%, which is better than that of pristine NCM811 (60.0%).

Preparation of Near Cube Form Calcite Type Calcium Carbonate Crystal from Dolomite and Its Mechanism

DENG Xiaoyang, ZHENG Qiang, QU Xiaoyuan, FAN Yuanyang, LIU Haili, CAO Xiaoning, YUE Yan, LI Xue

2022, 51(4):  704-715. 

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Near cube form calcite was prepared with light calcined dolomite powder, ammonium chloride and carbon dioxide as raw materials by ammonia-precipitation process without using crystal controlling agent. The effects of reaction temperature, calcium ion concentration in solution, aeration rate, agitation rate and aging time on the content of calcium carbonate and morphology of calcite phase in calcium carbonate were investigated, and the crystal type control mechanism of calcium precipitation reaction was studied. The results show that under the conditions of reaction temperature of 40 ℃, calcium concentration of 0.05 mol/L, carbon dioxide passing rate of 100 mL/min, stirring speed of 400 r/min and aging time of 2 h, near cube form calcium carbonate with regular morphology and uniform particle size distribution is prepared, with an average particle size from 5 μm to 10 μm. This study provides a theoretical basis for improving the use value of dolomite, producing calcium carbonate products with high added value and improving the utilization rate of dolomite resources.

Preparation and Characterization of TiB₂ and CNT Dual-Phases Toughened B₄C Ceramic Composites

XU Sen, LIN Wensong, ZHANG Hong, SHI Jianqiang, FANG Ningxiang

2022, 51(4):  716-722. 

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B₄C-TiB₂-CNT ceramic composites were fabricated by the liquid silicon infiltration (LSI) sintering at 1 500 ℃ in vacuum. The compositions, morphologies, mechanical properties and toughening mechanism of the fabricated composites were investigated. The results show that the main constituent phases of the composites are B₁₂(C, Si, B)₃, SiC and Si. The additions of TiB₂ and CNT significantly improve the mechanical properties of liquid-phase silicon sintered B₄C ceramics. The flexural strength and fracture toughness of the composite ceramics reach (390±18) MPa and (5.38±0.38) MPa·m^1/2 with TiB₂ and CNT additions of 10% and 0.4% respectively, which are 31% and 53% higher than pure B₄C caremics. The toughening mechanisms of B₄C-TiB₂-CNT ceramic composites are explained by the pullout of plate-like SiC particles and CNT, the particle toughening of TiB₂ and the deflection of cracks.

Mineralogical Characteristics and Spectroscopy of Yellow-Green Prehnite

WANG Qianqian, GUO Qingfeng, GE Xiao

2022, 51(4):  723-729. 

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Prehnite can be produced in the form of platy, schistose, botryoidalis, kidney, radial or massive aggregates. In recent years, prehnite has attracted the attention of many scholars due to its beautiful appearance and special crystal structure. In this paper, the composition, structure and spectral characteristics of yellow-green prehnite were investigated by the electron microprobe, powder X-ray diffractometer, fourier transform infrared spectrometer, micro-Raman spectrometer, and ultraviolet-visible spectrophotometer. The main chromogenic element of prehnite is Fe. Fe³⁺ often replaces Al³⁺ to occupy the octahedral coordination position, and Fe²⁺ often replaces Ca²⁺ into the lattice channel. The electron microprobe results show that the content changes of Fe and Al are negatively correlated as a whole, and the content changes of Fe and Ca are also negatively correlated as a whole. The samples with relatively high Fe content have a deeper yellow-green tone. XRD patterns and Raman spectra show that epidote exists in the form of inclusion in prehnite. Infrared and Raman spectra show that there are two framework of silicon-oxygen tetrahedron and aluminum-oxygen octahedron in prehnite. The UV-Vis absorption spectra reveal the chromogenic mechanism of prehnite. This paper systematically analyzes the mineralogical and spectral characteristics of prehnite, so as to provide ideas and experimental data for the further research of prehnite.

Reviews

Research Progress of Gallium Nitride Power Electronic Device Packaging Technology

FENG Jiaju, FAN Yaming, FANG Dan, DENG Xuguang, YU Guohao, WEI Zhipeng, ZHANG Baoshun

2022, 51(4):  730-749. 

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Gallium nitride (GaN) high electron mobility transistor (HEMT) has attracted much attention due to its high breakdown field strength, low on-resistance and high conversion efficiency, and it is expected to be applied in power electronics systems. However, its high power density and high frequency characteristics bring great challenges to packaging technology. The parasitic inductance parameters in the package of traditional silicon power electronic devices is large, which will cause switch oscillation and other problems, so that the excellent performance of GaN cannot be fully utilized. In addition, the thermal management ability of the package determines the reliability of the power device. If the self-heating effect of the device cannot be well solved, its performance will be reduced, and even the chip will be burned. On the basis of explaining the switching oscillation and thermal management problems caused by traditional packaging technology applied to gallium nitride power electronic devices, the research progress of GaN packaging technology aiming at the above problems are reviewed in detail in this paper, including by optimizing the control circuit, reducing L_g inductancing, improving R_g inhibition of dv/dt, increasing ferrite beads on the gate electrode, PCB layout optimization and increasing magnetic flux offset method to solve the problem of switch oscillation caused by the parasitic inductance, the application of high thermal conductivity material of diamond in devices thermal management, improvement of device package structure and other heat dissipation technologies.