Table of Content

15 March 2022, Volume 51 Issue 3

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Research Articles

Thermal Field Design and Optimization of Resistance Heated Large-Size SiC Crystal Growth System

LU Jiazheng, ZHANG Hui, ZHENG Lili, MA Yuan, SONG Depeng

2022, 51(3):  371-384. 

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Large-size, low-defect silicon carbide single crystal is one of the most important fundamental materials for power and radio frequency (RF) devices. The physical vapor transport (PVT) method is the major technique for growing large-size SiC single crystals currently. The core to obtain large-size and high-quality crystals is to find optimal matching conditions for vapor composition, temperature, and pressure at the crystal growth interface so that the vapor can crystallize evenly, at the same time the thermal stress in crystals is sufficiently small. This paper presents the numerical studies of the thermal field design for 8 inch SiC bulk crystal growth system with resistance heating. Specifically, the influences of heater position, heating power and the radiation aperture’s diameter on thermal field were studied, in conjunction with the optimal system structure. Numerical simulation results show that optimizing design parameters such as the shape of heat dissipation hole and the structure of insulation can achieve thermal fields with low horizontal temperature gradient and high axial temperature gradient desirable for the growth of large-size SiC crystal by resistance heating system while the thickness of grown crystal changes and porous raw material is consumed.

Process Control and Optimization of Ingot Crystalline Silicon Growth Using Neural Network and Genetic Algorithm

HAO Peiyao, ZHU Jinwei, LIAO Jilong, ZHENG Lili, ZHANG Hui

2022, 51(3):  385-397. 

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Ingot crystalline silicon is one of the important sources for solar-grade crystalline silicon materials. For reducing the cost of silicon wafers, it is necessary to develop large-size ingot crystalline silicon while ensuring the crystal quality. The core parameters that affect the quality of cast crystalline silicon include the ratio of crystal growth rate to temperature gradient at the solidification interface V/G, wall heat flow q, height difference of solidification interface Δh, and temperature difference of silicon melt ΔT. Aiming at the quality control during the growth of ingot crystalline silicon, this study established a process control optimization method based on the artificial neural network (ANN) model for the crystal growth process. A process control data set for the growth process of ingot crystalline silicon was constructed based on the experimental measurement data and numerical simulation results. The opening of the bottom insulation cage and the power ratio of the side and top heaters were used as the main process control parameters, and V/G, |q|, |Δh|, ΔT are the optimization goals. A neural network model for mapping the relationship between process control parameters and thermal field characteristics was established. The influence of the bottom heat insulation cage opening and the power ratio of the side to top heaters on the thermal field during the crystal growth process were analyzed using the trained neural network model. The process control parameters for the ingot crystalline silicon growth process are optimized using genetic algorithm (GA), improving the quality of grown crystal and reducing energy consumption. Finally based on the experimental test images, the influences of V/G on the crystal quality were discussed. Research shows that V/G in the middle stage of crystal growth changes smoothly along the horizontal direction, and the corresponding defects are less and evenly distributed. Therefore, increasing the uniformity of V/G in the horizontal direction is also an important factor to improve the quality of crystal.

Characterization of Third Harmonic Generation of High Power Nanosecond Laser on Nonlinear Optical Crystal Na₃La₉O₃(BO₃)₈

TANG Guangxin, LIU Wang, WANG Lirong, LI Yunfei, ZHANG Ling, ZHANG Guochun

2022, 51(3):  398-403. 

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The characteristics of 355 nm ultraviolet (UV) nanosecond (ns) laser generation using third harmonic generation (THG) method based on the new nonlinear optical (NLO) crystal Na₃La₉O₃(BO₃)₈(NLBO) were investigated. A Q-switched high-power 1 064 nm laser with repetition frequency of 10 kHz and pulse width of 10 ns was applied as the fundamental laser source. A type I phase-matched LBO crystal was used for the second harmonic generation (SHG) and a type I phase-matched NLBO crystal was used for the THG. The output power of 355 nm UV laser is 152.5 mW, and this is the highest output power of 355 nm UV laser generated by NLBO crystal. The variation of the crystal deflection angle with temperature when the NLBO crystal achieved the optimal THG output was studied, and the optimum phase matching angles at different temperatures were modified.

In Situ ATR-IR Investigation on the Crystallization of DKDP Crystals

LIU Fafu, ZHANG Cong, GUO Jianbin, ZHANG Wu, CAO Jianwu, ZHANG Haibo, XU Mingxia

2022, 51(3):  404-410. 

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The crystallization of KH_2-xD_xPO₄ (DKDP) crystals with different deuterium contents ranged from 0 to 99% were investigated in solution by Attenuated Total Reflectance Infrared (ATR-IR) spectroscopy. The (H₂PO₄^-)_1-x(D₂PO₄^-)_x ionic groups were characterized by the υ₁(PO₄) and υ₃(PO₄) vibrations. The intensity changes of the υ₁(PO₄) vibration peaks and the broadened width changes of the υ₃(PO₄) vibration peaks indicate that the (H₂PO₄^-)_1-x(D₂PO₄^-)_x concentration increases with the measurement time increases. Besides, the appearance of δ(P—O…H/D—O—P) vibration illustrates the formation of (H₂PO₄^-)_n-x(D₂PO₄^-)_x clusters, which can be confirmed as growth unite.The intensity changes of the H—O—H and D—O—D vibration at the wavenumbers from 1 448 cm^-1 to 1 653 cm^-1can illustrate the un-uniform distribution of deuterium contents in DKDP crystallization process.

Properties of Novel Ternary Relaxor Ferroelectrics Modified by Bismuth Series Compounds

HUANG Jiangfeng, WANG Tao, WANG Fenghua, HE Zhixing, CHEN Zhe, HUANG Yinbo, WU Wenjuan

2022, 51(3):  411-418. 

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As a traditional dielectric capacitor material, barium titanate (BaTiO₃) ceramics have strong ferroelectric property, which leads to low energy storage density. However, the relaxation ferroelectric can be obtained through doping to weaken the ferroelectric property and improve the energy storage performance. In this paper, BaTiO₃-based ceramics modified by BiScO₃ and (Sr_0.7Bi_0.2)TiO₃, a ternary ceramic material (0.99-x)Ba(Zr_0.1Ti_0.9)O₃-x(Sr_0.7Bi_0.2)TiO₃-0.01BiScO₃(abbreviated as BZT-xSBT-BS) was designed, owing to the enhanced relaxation properties induced by bismuth series compounds. The phase structure of BZT-xSBT-BS ceramics prepared by traditional solid-state method is not changed due to doping, and they are pure cubic perovskite structure at room temperature. Dielectric and ferroelectric tests and analysis show that BZT-xSBT-BS ceramics have typical relaxor ferroelectric properties. Sr²⁺ and Bi³⁺ ions substitutions produce thermionic relaxation polarization, which contributes to the polarization and increases the dielectric constant of BZT-xSBT-BS ceramics, but the dielectric loss will increase due to its slow response speed. An appropriate amount of (Sr_0.7Bi_0.2)TiO₃ can improve the dielectric, ferroelectric, strain and energy storage properties of BZT-xSBT-BS ceramics. BZT-xSBT-BS ceramics with x=0.015 show excellent properties, ε_r~10 372, tanδ~0.019, P_max=16.42 μC/cm², E_c=1.41 kV/cm, S⁺_max=0.12% (@40 kV/cm), W_D=0.181 J/cm³, η=79.4% (@60 kV/cm).

Very Low Frequency Broadband Gap Mechanism of Tian-Shaped Seismic Metamaterials

LI Lixia, LI Pengguo, JIA Qi, LI Ling

2022, 51(3):  419-427. 

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The seismic waves propagating in the earth mainly include body wave and surface wave, and Rayleigh wave in surface wave has the strongest damage to buildings. For the vibration control of Rayleigh waves, a Tian-shaped metamaterial structure was proposed. Compared with the traditional seismic metamaterials, this metamaterial barrier is composed of a nested cross column inside an external oral frame, forming four filling areas. The external frame is partially embedded, with high strength, strong stability and flexible filling methods. The band structure and transmission characteristics of Tian-shaped metamaterial were calculated by finite element method. By analyzing the mode shapes at the band gap boundary, it is found that the band gap opening is due to the local resonance of the cylinder. Combined with the band gap mechanism, different amounts of filling in the cylinder structure can change the quality of the column structure, form different resonant frequencies, and produce a very low frequency band gap. Furthermore, the mass filling methods with positive and negative gradients were designed and studied to broaden the band gap, and 3.3~13.1 Hz very low frequency broadband gap can be obtained. In the resonant frequency range, the isolation methods of the two are Rayleigh wave rainbow capture and Rayleigh wave to body wave conversion. Finally, the EI-Centro seismic wave was used to verify the time history of the filled barrier. The maximum acceleration attenuation is more than 80%, which provides new design ideas and methods for seismic metamaterials in damping and isolation.

Growth of Ultrafine Single-Crystal Fibers by Laser Heated Pedestal Growth Technique

WANG Tao, JIA Zhitai, LI Yang, ZHANG Jian, TAO Xutang

2022, 51(3):  428-433. 

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Single-crystal fiber (SCF) is a kind of fibrous functional crystalline material with “quasi one-dimensional” structure, exhibiting great application prospects in the fields of high-energy lasers, high-temperature sensing, radiation detection, information communication and other areas of national defense and national livelihood. In this work, ultrafine Al₂O₃ and YAG single-crystal fibers with the diameter from 60 μm to 100 μm and length-to-diameter ratio greater than 6 000∶1 were grown by laser heated pedestal growth (LHPG) technique. The diameter fluctuation of the obtained SCF is less than 4%, demonstrating excellent flexibility and waveguide characteristics. This work presents feasible approach for the miniaturization of SCF devices method.

Doping, Passivation and Photovoltaic Properties of Ultra-Thin Poly-Silicon

SONG Zhicheng, YANG Lu, ZHANG Chunfu, LIU Dawei, NI Yufeng, ZHANG Ting, WEI Kaifeng

2022, 51(3):  434-440. 

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The doping process, passivation and photovoltaic properties of 70 nm ultra-thin poly-silicon were studied in this paper. The optimal doping process for 70 nm ultra-thin poly-silicon was identified, the results show that when the ion implantation dose is 3.2×10¹⁵ cm^-3 and annealed at 855 ℃ for 20 min, the passivation properties of 70 nm ultra-thin poly-silicon is comparable to that of conventional 120 nm poly-silicon, and the surface doping concentration value of 5.6×10²⁰ atoms/cm³ for 70 nm ultra-thin poly-silicon is achieved, which is much higher than that of 120 nm doped poly-silicon (2.5×10²⁰ atoms/cm³). Based on the characteristic of reduced thickness and heavy doping for 70 nm ultra-thin poly-silicon, the conversion efficiency of TOPCon solar cells processed on large area (6 inch) Cz wafers significantly improves due to the low parasitic absorption and excellent filed passivation effect. The I_sc is increased by 20 mA and 0.3% improvement of FF, leading to an absolute efficiency gain of 0.13% for the champion conversion efficiency, as well as low series resistance.

Electron Transport Properties of ε-(Al_xGa_1-x)₂O₃/ε-Ga₂O₃ Heterojunction

BAI Yanan, LYU Yanwu

2022, 51(3):  441-449. 

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Ga₂O₃is an emerging wide bandgap semiconductor with potential applications in power and RF electronic systems. Previous studies have focused on β-Ga₂O₃, and theoretical caculations have been made on the two-dimensional electronic gas(2DEG) in β-(Al_xGa_1-x)₂O₃/Ga₂O₃ heterojunction. In this paper, the effect of ε-(Al_xGa_1-x)₂O₃ as a potential barrier on the electron transport properties of ε-(Al_xGa_1-x)₂O₃/ε-Ga₂O₃ heterojunction was studied. Firstly, the structure and properties of ε-(Al_xGa_1-x)₂O₃/ε-Ga₂O₃ heterojunction are introduced. The charge density on the polarization surface caused by spontaneous polarization and piezoelectric polarization of ε-(Al_xGa_1-x)₂O₃/ε-Ga₂O₃ heterojunction and the effect of polarization on the concentration of 2DEG were analyzed and calculated. Then, the relationship between ε-(Al_xGa_1-x)₂O₃ barrier thickness and alloy disorder scattering, interface roughness scattering and polar optical phonon scattering were analyzed under different Al mole composition. Finally, it is concluded that the interface roughness scattering and polar optical phonon scattering have important effects on the electron transport properties of ε-(Al_xGa_1-x)₂O₃/ε-Ga₂O₃ heterojunction, and the alloy disorder scattering has little effect on the electron transport properties of ε-(Al_xGa_1-x)₂O₃/ε-Ga₂O₃ heterojunction. The electron mobility of 2DEG concentration, alloy disorder scattering, interface roughness scattering and polar optical phonon scattering are determined by the thickness of ε-(Al_xGa_1-x)₂O₃ barrier layer and the Al mole composition.

Theoretical Study on Photocatalytic Activity of X/g-C₃N₄ (X=g-C₃N₄, AlN and GaN) Heterojunction

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

2022, 51(3):  450-458. 

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The stability, electronic structures, work function, and optical properties of single-layer g-C₃N₄ and X/g-C₃N₄(X=g-C₃N₄, AlN and GaN) heterostructures were investigated using plane-wave density functional theory with ultra-soft pseudopotentials. The results show that the lattice mismatch ratio and lattice mismatch energy of X/g-C₃N₄ heterojunction are very low, indicating that X/g-C₃N₄ heterojunction has excellent stability. Compared with the single-layer g-C₃N₄, the bandgap of the X/g-C₃N₄ all reduces, and the peaks and troughs of the density of states greatly improves. At the same time, X/g-C₃N₄ has a redshift, which leds to an increase in the number of electrons in the excited state, making electronic transitions easier. It shows that the heterojunction is beneficial to improves the response-ability of the system to visible light, and effectively improves the photocatalytic activity of the system. Further calculations show that the work function of X/g-C₃N₄ reduces and a built-in electric field is formed at the interface, which inhibits the recombination of photo-generated electron-hole pairs. This is of great benefit to the migration of carriers and the improvement of photocatalytic ability. Among them, the GaN/g-C₃N₄ heterojunction has the smallest work function, the potential difference at the interface formed a built-in electric field and the redshift is the most obvious. It can be inferred that the GaN/g-C₃N₄ heterojunction has the best photocatalytic activity. Therefore, the heterojunction proposed in this paper is an effective means to improve the photocatalytic activity of the system.

First-Principles Study on the Electronic Structure and Optical Properties of GeS/MoS₂ Heterojunction

LIANG Zhihua, TAN Qiuhong, WANG Qianjin, LIU Yingkai

2022, 51(3):  459-470. 

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Two-dimensional layered materials represented by MoS₂ and GeS exhibit excellent physical properties in optical and electrical aspects. How to combine the excellent properties of the two materials and obtain composite materials with new synergistic functions are of great significance to the development and application of electronic devices. This work uses the first-principles calculation method of density functional theory to systematically study the electronic structures and optical properties of GeS/MoS₂ heterojunctions, at the same time, the influence of interface distance, strain and electric field on the electronic structures and the optical properties of the heterojunctions was also explored. The research results show that the GeS/MoS₂ heterojunctions is a type Ⅱ band arrangement, which is conducive to the separation of photogenerated electron-hole pairs. Further research found that the band arrangement and light absorption coefficient of GeS/MoS₂ heterojunctions can be effectively controlled by means of strain and electric field. The research results show that GeS/MoS₂ heterojunctions has potential applications in photocatalysis, optoelectronic devices and other fields, and the research in this paper provides theoretical guidance for the design and preparation of GeS/MoS₂ related optoelectronic devices.

Frist-Principles Study on Electric Structure of Ag-O Co-Doped p-Type AlN Nanotubes

XIONG Mingyao, ZHANG Rui, WEN Dulin, SU Xin

2022, 51(3):  471-476. 

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Based on the first-principles plane wave ultrasoft pseudopotential method, the geometric structure of (6, 0) single-wall aluminum nitride nanotubes, Ag doped, and Ag-O co-doped nanotubes were optimized.This work discusses the energy band structure, density of states and differential charge density of aluminum nitride nanotubes before and after doping. The results show that the band gaps of intrinsic AlN nanotubes, Ag doped AlN nanotubes and Ag-O co-doped aluminum nitride nanotubes are 2.49 eV, 1.84 eV and 1.80 eV. All doping configurations still preserve semiconductor characteristics. Based on the present discussion, the top of the valence band of Ag doped AlN nanotubes penetrates through the Fermi level to form a degenerate state, which realizes the p-type doping of AlN nanotubes. However, there is a strong hybrid effect between the electronic orbitals of Ag-4d state and N-2p state,the mono-doping of Ag is in general energetically unfavorable. After O doping, Ag and O attracts each other to overcome the repelling of acceptor Ag atoms, which makes the doping of Ag in AlN nanotubes more stable; the band gap of co-doped nanotube system is narrower than that of single doped nanotube system, and the conductivity is further enhanced. Ag-O co-doping is expected to be an effective method to obtain p-type AlN nanotubes.

Theoretical Studies of the Thermal, Electronic and Mechanical Properties of Ti₃(Zn_xAl_1-x)C₂ Solid Solutions

DENG Feiran, XU Min, MIAO Feng, HUANG Yi, FENG Shiquan, SONG Mingze, XIAO Chenda, LIN Yuanyuan, LI Huimin

2022, 51(3):  477-484. 

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Using the first-principles density functional theory plane-wave pseudopotential method, the Ti₃(Zn_xAl_1-x)C₂ structure, energy, phonon properties, electronic properties and elastic properties were systematically studied by projector augmented wave (PAW) and generalized gradient approximation (GGA). The structure model of Ti₃(Zn_xAl_1-x)C₂(x=0, 0.25, 0.5, 0.75, 1) solid solutions were constructed by substituting Zn for Al element at A position in Ti₃AlC₂ crystal of MAX phase. The calculation analysis shows that Ti₃(Zn_xAl_1-x)C₂ solid solutions are a thermodynamic, dynamic and mechanically stable brittle material in the doping concentration range studied. In addition, Ti₃(Zn_xAl_1-x)C₂(x=0, 0.25, 0.5, 0.75, 1) solid solutions are metallic. The electronic density of states at Fermi level mainly contributes from the Ti-3d state, and possesses the comprehensive properties of ionic, covalent and metallic bonds. The conductivity and plasticity of Ti₃(Zn_xAl_1-x)C₂(x=0, 0.25, 0.5, 0.75, 1) solid solutions are enhanced to some extent with the increase of Zn doping concentration.

Two Supra Molecular Co(Ⅱ) Coordination Polymers Based on 2,5-Dimethoxyterephthalic Acid and Imidazole Derivatives: Crystal Structures and Photo-Catalytic Reactions

SHI Mingfeng, GU Jianghong, LU Senyuan, XU Zhongxuan

2022, 51(3):  485-492. 

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Two cobalt coordination polymers, namely{[Co(DTA) (1,4-DIB)(H₂O)]·H₂O}_n (1) and [Co(DTA)(1,3-BMIB)]_n(2) were constructed by 2,5-dimethoxyterephthalic acid (H₂DTA), Co(Ⅱ) ions and different imidazole derivatives 1,4-di(1H-imidazol-1-yl)benzene (1,4-DIB) and 1,3-bis(4-methyl-1H- imidazol-1-yl)benzene (1,3-BMIB) under hydrothermal reaction, respectively. Complexes 1 and 2 were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, thermo-gravimetric analysis and UV-Vis spectra. Single-crystal X-ray diffraction reveals that complexes 1 and 2 are three-dimensional supra molecular frameworks packed by two-dimensional layers. The powder X-ray diffraction confirms that complexes 1 and 2 are stable in water under UV light. The UV-Vis spectra indicate that complexes 1 and 2 are semiconductors with high absorbing ability for UV-Vis light. Photocatalytic tests further confirm the complex 1 and 2 have catalytic activity for the degradation of methylene blue (MB) in water.

Alkali Resistance of Iron Vanadium Based Oxides by SAPO-34

HU Fangfang, LI Shun, CAI Sixiang, JIANG Hong, MA Yanping

2022, 51(3):  493-501. 

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Fe-VO_x/SAPO-34 and Fe-VO_x/TiO₂ catalysts were prepared by impregnation method to explore the catalytic activity and alkali metal resistance of SAPO-34 molecular sieve and TiO₂ supported iron vanadium-based oxides. The catalysts were characterized by means of XRD, XPS, NH₃-TPD, H₂-TPR and in-situ DRIFTs. The results show that: the specific pore structure and stable skeleton in SAPO-34 molecular sieve are conducive to the uniform dispersion of active components on the carrier and reduce the physical coverage of alkali metals on the surface active centers; at the same time, the rich acid sites can be used as alkali metal capture sites to protect the active center on the catalyst surface and ensure the normal adsorption reaction process of the catalyst, so that Fe-VO_x/SAPO-34 shows good alkali metal resistance.

Preparation of Tin Dioxide/Bismuth Tungstate Composite Photocatalytic Materials by Hydrothermal Method and Its Catalytic Activity

ZHENG Wenli, LIU Jiaqi, WU Zhaoyang, LIU Mengfan, ZHANG Hengqiang, HAN Wei

2022, 51(3):  502-507. 

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In this paper, the orthorhombic nano-spherical tin dioxide and orthorhombic bismuth tungstate which are aggregated from flake to spherical structure were prepared by hydrothermal method, and then they were compounded to prepare the composite photocatalytic material of tin dioxide/bismuth tungstate. X-ray diffraction (XRD), scanning electron microscope (SEM), specific surface area tester (BET) and UV-Vis spectrophotometer were used to characterize the structure, morphology, specific surface area, pore volume and aperture and optical properties of the composite samples. The photocatalytic activity of tin dioxide/bismuth tungstate composites was studied by iodine tungsten lamp to simulate sunlight and using tin dioxide, bismuth tungstate and tin dioxide/bismuth tungstate composites as catalysts to degrade rhodamine B(RhB). The degradation rates of rhodamine B by tin dioxide, bismuth tungstate and tin dioxide/bismuth tungstate are 9%, 22% and 30%, respectively. Experiments show that the photocatalytic activity of tin dioxide/bismuth tungstate composite is higher than that of single tin dioxide and bismuth tungstate under visible light.

Influence of Stoichiometric Ratio on the Microwave Dielectric Properties of MgO·nGa₂O₃ Spinel Ceramics

YANG Ming, XU Pengyu, WANG Bin, ZHENG Kaiping, TU Bingtian, WANG Hao

2022, 51(3):  508-515. 

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Spinel-type microwave dielectric ceramics are widely applied in wireless communication due to its high quality factor and adjustable resonant frequency temperature coefficient. In this paper, MgO·nGa₂O₃ (n=0.975, 1.00, 1.08 and 1.17) spinel ceramics were prepared by pressureless sintering. The influence of stoichiometric ratio on the crystalline structure was studied by the XRD Rietveld whole pattern fitting method. The relationship between microwave dielectric properties and crystalline structure was explored through the bond valence theory model. The variation of relative dielectric constant (ε_r) of MgO·nGa₂O₃ ceramics is related to the lattice constant and ion polarizability. The quality factor (Q×f) decreases from 165 590 GHz to 109 413 GHz as n increases, which is affected by bond strength and the degree of cation order. The resonant frequency temperature coefficient (τ_f) is related to the crystal thermal expansion coefficient. The obtained MgO·0.975Ga₂O₃ ceramics possess excellent microwave dielectric properties: ε_r=9.69, Q×f=165 590 GHz (at 14 GHz) and τ_f=-7.12×10^-6/℃.

Amino Acids/Graphene Oxide/Hydroxyapatite Composites on in vitro Remineralization of Acid-Etched Human Enamel

CAI Ying, CHUAN Dingze, CHEN Qinghua, LIU Jitao

2022, 51(3):  516-522. 

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Effects of glycine (Gly) and graphene oxide (GO) modified hydroxyapatite (Gly/GO/HA), and aspartic acid (Asp) and GO modified hydroxyapatite (Asp/GO/HA) on in vitro remineralization of acid-etched human enamel (HE) were investigated. The cytotoxicity of these composites was studied by CCK-8 method, the surface and cross-section morphology, surface element composition, surface composition structure and surface mechanical properties of HE before and after remineralization were characterized by field emission scanning electron microscope, EDX energy spectrum analysis, X-ray diffraction and microhardness test. The results show that Gly/GO/HA and Asp/GO/HA both have good safety and biocompatibility, and both can repair the acid-etched HE to a certain extent, among which Gly/GO/HA is better than Asp/GO/HA in repairing the surface and deep demineralization of the acid-etched HE.

Reviews

Research Progress of Ultra-Wide Band Gap Semiconductor Ga₂O₃-Based X-Ray Detectors

LI Zhiwei, TANG Huili, XU Jun, LIU Bo

2022, 51(3):  523-537. 

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X-ray with its advantages of short wavelength and strong penetration plays an important role in medical imaging, security inspection, scientific research, space communication, and other fields. Semiconductor X-ray detectors can convert X-ray photons into current signals, which have the advantages of easy integration, high spatial resolution, high energy resolution, and fast response speed. High-performance X-ray detectors should have the features of low dark current, high sensitivity, fast response speed, and stable work for a long time. Therefore, the semiconductor materials for preparing X-ray detectors should have the characteristics of high resistivity, few defects, and strong irradiation resistance. Gallium oxide (Ga₂O₃) is one of the new wide band gap semiconductor materials, which has the advantages of ultra-wide band gap, high breakdown field strength, high X-ray absorption coefficient, high thermal stability, and being grown by melting methods. Therefore, Ga₂O₃ is suitable for preparing X-ray detectors. In recent years, X-ray detectors based on Ga₂O₃ have become one of the research hotspots. In this review, the physical properties of Ga₂O₃ semiconductor and its research progress in X-ray detectors are introduced, the influence mechanism of materials and device structure on the performance of X-ray detectors are analyzed, the ideas for the preparation of Ga₂O₃-based X-ray detectors with high performance are provided.

Progress in the Preparation and Opto-Electro-Magneto Application of Two-Dimensional Layered Metal Iodides

PAN Baojun, ZHANG Lijie, WANG Peijian

2022, 51(3):  538-550. 

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Novel layered metal iodides, with a van der Waals stacking structure and large average atomic numbers, suitable energy band-gap, strong magnetoelectric coupling effect, are regarded as a new type of photoelectric detection material, including high-energy ray detectors. Some magnetic 2D metal iodides can be used in magneto-electronic devices. Due to the strong potential for applications in opto-electro-magneto devices, they become a hot research topic in low-dimensional materials. Moreover, in terms of material preparation, the generally low melting points, mild and simple preparation conditions make layered metal iodides a good candidate to explore the growth mechanisms of two-dimensional layered materials. The structure and properties of 2D metal iodides are introduced in this paper, and then focus on the preparation of two-dimensional layered metal iodides. Finally, their applications in opto-electro-magneto devices are discussed. Hopefully, the readers will gain a better understanding of two-dimensional layered metal iodides and largely promote their future applications.

Research Progress of Low Lead/Lead-Free Perovskite Solar Cells

YANG Zhisheng, KE Weifang, JIAO Xuewei, YU Zenan, ZHU Hua

2022, 51(3):  551-558. 

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As a new low-cost and high-efficiency photovoltaic material, perovskite solar cells have attracted much attention in recent years. Lead based perovskite solar cells have the advantages of high photoelectric conversion efficiency, low cost and easy preparation. However, their further commercialization and application are greatly limited due to the toxicity issue of lead and environmental pollution caused by lead. Therefore, some novel non-toxic or low-toxic perovskite materials have been explored for development of environmentally friendly low lead/lead-free perovskite solar cells. ⅣA group elements Ge, ⅡA group elements Mg, Ca, Sr and Ba, ⅤA group elements Bi and Sb, ⅢA group element In and transition metal element Cu are used to replace or partially replace Pb. This article briefly introduces the structure and formation conditions of hybrid perovskite materials, and focuses on the development of Sn based perovskite solar cells. The performance regulation of low lead or lead-free perovskite materials by adjusting the composition and ratio of halogen X and positive ion A are summarized. And the research progress of low lead/lead-free perovskite solar cell devices is reviewed. In addition, their future development direction is prospected.

Synthesis of Jadeite: Review and Perspective

OUYANG Liuzhang, HE Fei, XING Yingying

2022, 51(3):  559-570. 

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Over the centuries, with the vigorous development of craftsmanship and the jewelry industry, the demand of jadeite, known as the “king of jade”, has increased sharply in decoration and collection. However, the formation conditions of jadeite in nature are extremely harsh, which makes it difficult for its supply to meet people’s needs. Therefore, the development of jadeite synthesis technology is of great benefit to the problem of insufficient supply of natural jadeite. It can not only promote the high yield of jadeite, but also can accelerate its marketization process. High temperature and high pressure method has been widely used to synthesize artificial jadeite. The key to this method is the synthesis of jadeite precursors and the conversion of vitreous amorphous jadeite to jadeite. In this process, to prepare the jadeite precursor under a relatively mild condition is thus a key point, but several challenges still remained. This review discusses the latest research hotspots and applications of jadeite synthesis at home and abroad in recent years, focusing on three conventional preparation techniques for jadeite precursors: solid-phase sintering method, chemical synthesis method and sol-gel method. At the same time, the advantages and disadvantages of various methods are evaluated, and the future development of artificial synthetic jadeite is also prospected.