Table of Content

15 March 2024, Volume 53 Issue 3

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Special Issue on Lithium Niobate Integrated Photonics

Defect Structure of Lithium Niobate Crystals

LIU Hongde, WANG Weiwei, ZHANG Zhongzheng, ZHENG Dahuai, LIU Shiguo, KONG Yongfa, XU Jingjun

2024, 53(3):  355-371. 

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Lithium niobate is an artificial crystal which integrates electro-optic, acousto-optic, piezoelectric and nonlinear properties, and has been known as “optical silicon” or “photonic silicon”. In recent years, with the rapid development of integrated photonics based on thin film lithium niobate, lithium niobate crystals have received more and more attention. However, lithium niobate is a typical non-stoichiometric crystal, it contains a large number of intrinsic defects, which seriously affects its characteristics. The lithium niobate lattice has good solid-solution to many impurity ions, moreover, its properties vary significantly with the types and concentrations of dopants. As with defect engineering of semiconductors such as silicon, defects have and will continue to have an important effect on crystal performance and integrated photonics based on thin film lithium niobate. This paper briefly reviews the defect structure of lithium niobate crystals, especially the recent progress on thin film lithium niobate crystals, including the intrinsic defect structure, extrinsic defect structure, characterization of defect structure, theoretical calculation of defect structure, and structure-activity relationship between defect structure and crystal properties. We hope it helpful to the current research of lithium niobate integrated photonics.

Advances in Low-Loss Thin-Film Lithium Niobate Photonic Integrated Devices

LIN Jintian, GAO Renhong, GUAN Jianglin, LI Chuntao, YAO Ni, CHENG Ya

2024, 53(3):  372-394. 

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Recently, due to the rapid development of ion-slicing technique and low-loss nanostructuring technology for thin-film lithium niobate (TFLN), photonic integrated microstructures have been demonstrated on the TFLN platform with high-performances, allowing tight optical field confinement, ultralow propagation loss, fast electro-optic tunability, highly efficienct optical frequency conversion, and strong acousto-optic modulation. This technological advance in turn results in a variety of innovative photonic integrated devices of unprecedented optical qualities, such as meter-scale length electro-optically switchable optical true delay lines, ultrahigh-speed electro-optic modulators, efficienct frequency convertors, on-chip frequency combs, miniaturized microwave sources, bright quantum light sources, high-power waveguide amplifiers, narrow-linewidth microlasers, and compact ultrafast light sources. Up to now, the TFLN photonics is making a great advance in large-scale photonic integrated circuits, and opening an avenue for the further development for fast information processing, precision metrology, integrated quantum information processing and artificial intelligence, enabled by the advances in low-loss wafer-scale nanofabrication technology and the outstanding properties of TFLN. This review begins with the history of bulk lithium niobate optics, and then we survey the development history of ion-sliced TFLN wafer and nanofabrication technologies for TFLN photonic structures. The following sections present various TFLN photonic integrated devices categorized into nonlinear photonics, frequency comb generation, electro-optical modulators, wavelength/mode division multiplexers and coherent light sources. Finally, some conclusions and future perspectives are provided.

Conductive Domain Wall and Its Applications in Lithium Niobate

ZHANG Yuchen, LI Sanbing, XU Jingjun, ZHANG Guoquan

2024, 53(3):  395-409. 

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Lithium niobate (LiNbO₃, LN) is a kind of multi-functional uniaxial ferroelectric material, and is widely used in optical modulators, optical frequency combs, optical waveguides, and so on. The emergence of conductive domain wall (DW), serving as a nanoscale conductive path embedded in the insulating materials and showing important application prospects in non-volatile memristor, logic gate, and transistor, etc., promoted the application of LN in the field of nano-opto-electronics. The realization of DW p-n junction in LN on an insulator (LNOI) is expected to push forward the development of opto-electronics integrated chips based on LN. This paper provides a concise review on the study of DWs in LN, including the fabrication techniques, the conduction mechanism and types of DWs as well as the development of applications based on DWs, especially the achievement of DW p-n junction. Furthermore, combined with the hot potential applications, the key issues, challenges and opportunities in the development DW-based opto-electronic devices based on LN were summarized.

Recent Research Progress of Thin film Lithium Niobate Photodetector

XIE Hanrong, YANG Tiefeng, WEI Yuming, GUAN Heyuan, LU Huihui

2024, 53(3):  410-425. 

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Lithium niobate crystal has many advantages such as large electro-optical, piezoelectric and non-linear optical coefficients, wide optical transparency range, compatibility with speed matching, phase matching and dispersion engineering, long-term stability and low-cost preparation of optical-grade wafers. As an important platform for constructing optoelectronic devices such as electro-optic modulators, optical frequency combs and optical waveguides, lithium niobate holds grant promise in the fields of light generation, light transmission and light modulation in the field of information and communication. Lithium niobate is also well known as the “silicon of photonics” and has huge integration potential in both academia and industry. However, due to the insulator and weak optical absorption properties of lithium niobate, integrated application fields based on lithium niobate platforms also face the problems of low photo-to-electric conversion efficiency and thus arouse difficult in photodetection. Light demodulation and light extraction in all-optical communications require high-performance detectors, therefore, the development of photodetectors based on lithium niobate has great scientific significance and application value. Starting from the basic structural characteristics of lithium niobate, this article introduces in detail the excellent physical properties and photo-to-electric conversion mechanism of lithium niobate, reviews some recent research results of domestic and foreign scholars, and focuses on the optical waveguide integrated photodetectors and the heterogeneous type photodetectors based on lithium niobate crystals, the advantages and development potential of different routes are discussed and compared, and prospects for this field are proposed.

Fabrication and Characterization of Wafer-Scale Thin-Film Lithium Niobate Waveguides

YE Zhilin, LI Shifeng, CUI Guoxin, YIN Zhijun, WANG Xuebin, ZHAO Gang, HU Xiaopeng, ZHU Shining

2024, 53(3):  426-433. 

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With the rapid development of photonic integration and optical communication technology, low-loss waveguides have become the key components for efficient photonic transmission, and their performance directly affects the performance of the entire integrated chip. Therefore, the preparation technology of low-loss thin film lithium niobate (TFLN) waveguides is currently a hot and difficult research topic. In this study, in-depth research on the preparation process of wafer-level low-loss thin-film lithium niobate waveguides was conducted. On a 4-inch thin-film lithium niobate wafer, waveguides with a transmission loss of less than 0.15 dB/cm based on the deep-UV lithography and inductive coupled plasma etching were successfully prepared, while the etching depth error was controlled within 10%, greatly improving the accuracy of the waveguide structure. Additionally, this study also proposed a characterization method based on micro-ring resonators for wafer-level waveguide loss measurement, which can more accurately evaluate waveguide performance. Through testing, it is found that the qualified rate of the prepared waveguides exceeds 85%, demonstrating good reproducibility and reliability. The wafer-level thin film lithium niobate processing technology developed in this article is of great significance for promoting the large-scale preparation and application of lithium niobate waveguides.

Growth of 8-Inch Lithium Niobate Crystals

SUN Dehui, HAN Wenbin, LI Chenzhe, PENG Liguo, LIU Hong

2024, 53(3):  434-440. 

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Lithium niobate film on insulator (LNOI) is increasingly applied in the field of key devices in the new generation of information technology. With the development of the techniques of lithium niobate single crystal thin film and photonic integrated circuits, low cost, high integration is the eternal development direction. Therefore, it is urgently needed the large-scale lithium niobate crystal. In this paper, the variation of natural convection of melt in large-sized crucible as the liquid level decrease was discussed, and the growth characteristics of Z- and X-axis lithium niobate crystal were discussed. The 8-inch Z- and X-axis lithium niobate crystals with the size of larger than ϕ210 mm×50 mm were obtained. The transmission of the spectral range of 380~3 300 nm is more than 70% for 1 mm thick X-axis lithium niobate wafers. The chip moire pattern images show the presence of refractive index ripple defects in the crystal, indicating that the quality of the crystal still needs improvement.

Study on Fabrication of Erbium-Doped Lithium Niobate Thin Film Based on Low Temperature Ion Exchange Method

HE Yuxuan, WU Jiangwei, CHEN Yuping, CHEN Xianfeng

2024, 53(3):  441-448. 

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In this paper, by preparing a molten mixture of KNO₃ and Er(NO₃)₃, mixing it with a thin film lithium niobate in a high-temperature tube furnace for low temperature thermal diffusion, and combining it with an annealing process, a method was invented to directly dope the thin film lithium niobate with Er³⁺. By continuously changing parameters such as thermal diffusion temperature, doping reagent concentration ratio and crystal tangential direction, the influence of different parameters on the effect of doping Er³⁺ by the low temperature ion exchange method was explored through comparative experiments. When the thermal diffusion and annealing temperature were 360 ℃, and under the parameter setting of KNO₃ and Er(NO₃)₃ mass ratio of 25∶1, a Z-cut erbium-doped thin film lithium niobate with good surface morphology was obtained. The Er³⁺ concentration in the obtained erbium-doped thin film lithium niobate was detected by time-of-flight secondary ion mass spectrometry, which verified the actual effect of the low temperature ion exchange method used. This method greatly simplifies the thin film lithium niobate doping process, while saving costs, and will help to achieve subsequent selectively doping on the thin film lithium niobate platform and provides a viable solution for the construction of a customized lithium niobate photonic integration platform in the future.

Poling Electric Field Uniformization Design Regulates the Duty Cycle of Periodically Poled Lithium Niobate

LIU Qilu, ZHENG Mingyang, GAO Yang, ZHANG Longxi, SONG Yukun, WANG Fulei, LIU Hong, WANG Dongzhou, SANG Yuanhua

2024, 53(3):  449-457. 

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In theory, quasi phase match (QPM) can make full use of nonlinear optical coefficient of the crystal, and has no deviation effect, which has great advantages in optical frequency conversion. Lithium niobate crystal (LiNbO₃, LN) has high nonlinear optical coefficient, wide optical range and low growth cost, causing the periodically poled lithium niobate crystal (PPLN) based on the design of ferroelectric domain structure is an ideal choice for QPM. At present, the most commonly used method for fabricating PPLN crystal is applied electric field method. In the fabrication process, the parameters of electrode structure are important for the poling process. Based on the electric field poling process under real-time monitoring and finite element analysis, this paper analyzed the spatial electric field distribution of different electrode structures. It is found that the electric field maximum appears at the edge of the electrode, the electric field distribution inside the electrode is relatively uniform. Based on this phenomenon, a design scheme of multi-channel electrode structure is proposed to achieve uniform distribution of electric field in poled area. By characterizing the duty cycle ratio of each channel, it is found that the duty cycle ratio of the inner eight channels are uniform and within 50%±5%. Through the SHG experiment of crystals, it is found that the nonlinear conversion efficiency of the inner channel relative to the edge channel in the sample of ten-channel periodic poling is significantly improved and uniformly distributed. It is proved that the middle channels have a uniform poling structure with controllable duty cycle, which provides an effective design for generating uniform poling electric fields.

Femtosecond Laser Direct Writing of Lithium Niobate Crystal Semi-Cladding Optical Waveguide

DUAN Yumeng, JIA Yuechen, LYU Jinman

2024, 53(3):  458-464. 

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In this paper, the semi-cladding waveguides with diameters of 30, 40 and 50 μm were successfully prepared in lithium niobate (LiNbO₃) crystals by femtosecond laser micro-nano-processing technology. Their waveguiding performances were tested by the end-face coupling technique, which results in the waveguides having excellent transmission performances at the wavelengths of 633 and 1 550 nm. The guidance is valid only for TM polarization with the single-polarized nature. By calculating the transmission loss of the waveguide, it is concluded that the 30 μm diameter waveguide has the best transmission performance at 633 and 1 550 nm wavelengths. The experimental results are proved to be reasonable by theoretical calculations using Rsoft software. The results of this study provide an important reference for the design and performance optimization of optical waveguides, and have certain experimental and theoretical value.

Integrated Lithium Niobate Polarization Beam Splitter Based on a Subwavelength Grating-Assisted Directional Coupler

CHEN Li, ZHOU Xudong, YUAN Mingrui, XIAO Huifu, TIAN Yonghui

2024, 53(3):  465-471. 

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Lithium niobate on insulator (LNOI) is an ideal platform for realizing high-speed photonic integrated circuits (PICs). By taking full advantage of LN, the LNOI platform enables high-speed electro-optic and efficient nonlinear optical integrated devices. The polarization beam splitter (PBS) is one of the key passive devices for separating and combining two orthogonal polarized modes, which is essential for realizing on-chip polarization multiplexing systems and enhancing the data transmission capacity of photonic communication systems. In recent years, PBS has been successfully implemented based on various structures. Among them, the PBS based on subwavelength grating-assisted directional coupling structure stands out due to its excellent device performance and compact size. In this paper, we present a high-performance PBS with a subwavelength grating-assisted directional coupling structure, realized through an indirect etching scheme of silicon nitride-lithium niobate heterogeneous integration. Simulation results show that the device achieves a polarization extinction ratio greater than 24.49 dB in the wavelength range of 1 500 nm to 1 600 nm. Experimental data further confirms that the polarization extinction ratio of the device is greater than 18.06 dB in the wavelength range of 1 500 nm to 1 580 nm.

Photovoltaic Transportation of Surfactant-Mediated Aqueous Microdroplets on LiNbO₃ Platform

SHI Lihong, GAO Zuoxuan, YAN Wenbo

2024, 53(3):  472-479. 

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A method of surfactant-mediated photovoltaic transportation is proposed in this paper, the surfactant (span 80) layers self-assembled at the water-oil and oil-LN interfaces are employed to isolate photovoltaic charges in this method. The reduced electrostatic attenuation, remarkable hydrophobicity, and strong electrical breakdown suppression of the surfactant layers enable the stable and swift transportation of fL-scale aqueous microdroplets using μW-level laser in an oil medium. Three kinds of microdroplet responses to the laser illumination (unresponsive, repulsive and attractive cases) was found. With the increase of surfactant concentration, the driving mechanism can transit from the coulomb repulsion to the dielectrophoretic attraction that facilitates the photovoltaic transportation. Besides, the minimal laser power required for the attractive response was found correlated with the NaCl concentration inside the microdroplet.

Research Articles

Dislocation Density Evolution Study of GaN Single Crystal Growth by Ammonothermal Method

XIA Zhenghui, LI Tengkun, REN Guoqiang, XIE Kaihe, LU Wenhao, LI Shaozhe, ZHENG Shunan, GAO Xiaodong, XU Ke

2024, 53(3):  480-486. 

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Gallium nitride (GaN) single crystal has the characteristics of high breakdown voltage, direct band gap, high saturated electron drift rate, good chemical stability, etc., and has been widely used in optoelectronic devices and high-power electronic devices. However, the heteroepitaxial of GaN produces a high dislocation density, which limits the performance of GaN devices. In this study, GaN single crystal was grown by ammonothermal method using HVPE-GaN as a seed crystal. The dislocation evolution from the seed crystal region to the lateral growth region of GaN single crystal was studied by scanning electron microscopy (SEM), optical microscopy and wet etching. The results show that the dislocation density of GaN single crystal in the lateral growth region is obviously lower than that in the seed crystal region, and the dislocation density decreases by 2 orders of magnitude when the lateral growth exceeds 25 μm.

Fabrication and Characterization of 8 Inch Semiconducting GaAs Single Crystal Substrate

REN Diansheng, WANG Zhizhen, ZHANG Shuhui, WANG Yuanli

2024, 53(3):  487-496. 

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Si doped GaAs single crystal with diameter over 200 mm was prepared by vertical gradient freeze (VGF) method. The 8 inch GaAs single crystal substrate was obtained through multi-line cutting, edging, grinding, chemical mechanical polishing and wet cleaning. The crystal quality, dislocation density, electrical properties and surface quality of 8 inch GaAs substrate were characterized by X-ray diffraction, dislocation density inspection, Hall measurement, non-contact surface resistivity measurement, photoluminescence and wafer surface defect inspection. The results show that the full width of half maximum (FWHM) of substrate (400) diffraction peak is smaller than 0.009°, the average dislocation density is lower than 30 cm^-2, the lowest dislocation density is 1.7 cm^-2 and 98.87% area are zero dislocation. Moreover, the standard deviation of surface resistivity and photoluminescence intensity are smaller than 6% and 4%, respectively. The number of the spot with light point defect (LPD)≥0.2 μm is less than 10. The results show that the 8 inch semiconducting GaAs single crystal substrate with excellent performance is developed and can be used as the high quality substrate for epitaxial growth and devices fabrication.

Preparation and Properties of 13N Ultra-High Purity Germanium Single Crystals

GU Xiaoying, ZHAO Qingsong, NIU Xiaodong, DI Juqing, ZHANG Jiaying, XIAO Yi, LUO Kai

2024, 53(3):  497-502. 

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13N ultra-high purity germanium single crystal is the core material for producing ultra-high purity germanium detectors. This article obtains reduced germanium ingots by reduction method, then purifies them by horizontal zone refining method to obtain 12N high-purity germanium polycrystals, and finally grows 13N ultra-high purity germanium single crystals by Czochralski method. The performance of 13N ultra-high purity germanium single crystal was tested and studied through low-temperature Hall test, dislocation density test, and deep level transient spectroscopy (DLTS) detection. The low-temperature Hall results show that the average mobility of the crystal head cross-section is 4.515×10⁴ cm²·V^-1·s^-1, the carrier concentration is 1.176×10¹⁰ cm^-3, and the conductivity is p-type, the dislocation density at the crystal head is 2 256 cm^-2. The average mobility of the tail section is 4.620×10⁴ cm²·V^-1·s^-1, the carrier concentration is 1.007×10¹⁰ cm^-3, and the conductivity type is p-type, the dislocation density at the tail of the crystal is 2 589 cm^-2. The concentration of deep level impurities in the crystal is 1.843×10⁹ cm^-3. The results indicate that the crystal is 13N ultra-high purity germanium single crystal.

Thermal Conductivity Test of Large-Size Diamond by Laser Flash Method

ZHANG Yalin, AN Xiaoming, GE Xingang, JIANG Long, LI Yifeng

2024, 53(3):  503-510. 

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In order to solve the problem of thermal conductivity test of large-size diamond, the ϕ100 mm sample holder of vertical mode and In-Plane mode was designed for the NETZSCH LFA467 HyperFlash instrument. The test results of the ϕ100 mm sample holder are proved to be credible from both principle and test results. From the theoretical analysis, it is concluded that the change of sample boundary conditions brought by the new sample holder has little effect on the test results. The thermal conductivity test results of the ϕ100 mm sample holder in the In-Plane mode are 6.5% higher than that of the standard sample holder, and the thermal conductivity test results of the ϕ100 mm sample holder in the vertical mode are 3.6% higher than that of the standard sample holder. The test results are still within the acceptable range. The ϕ100 mm sample holder designed in this paper can test ϕ100 mm samples at most, which helps to protect the integrity of samples. In this paper, the non-destructive testing of thermal conductivity of large-size diamond by laser flash method is realized.

Bandgap Characteristics of Metamaterial Sandwich Plates with Spiral Holes

ZHANG Jiulin, TIAN Xia

2024, 53(3):  511-518. 

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In this paper, a new type of low frequency broadband perforated metamaterial sandwich plate is designed to suppress the transverse vibration between the plates. The unit cell of the structure is composed of the upper and the lower layer plates, spiral plates, cylindrical oscillators and support components. Among them, the spiral plate with four threaded holes is connected with the upper and lower plates through the support parts on both sides, and the oscillator is fixed at the center of the plate by bolts. The finite element analysis of the cell is carried out by COMSOL Multiphysics, and the energy band structure and resonance mode of the infinite periodic structure are obtained. In addition, the transmission transmittance of the finite-period structure is calculated. The results show that the structure generate two wide band gaps of low frequency vibration, and the vibration attenuation is obvious in the band gap range. Furthermore, this paper unveils the mechanism of the band gap, optimizes structural parameters, achieves low-frequency coupling of the two band gaps, and provides band gap configurations that meet the practical engineering requirements.

First-Principles Study on the Photoelectric Properties of N and As Doped Two-Dimensional GeC

LI Ping, QIN Yanjun, PANG Guowang, TANG Yuzhu, ZHANG Yao, WANG Peng, LIU Chenxi

2024, 53(3):  519-525. 

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Based on the first-principles calculations of density functional theory, the stability, electronic structure, and optical properties of single layer GeC, N-doped, As doped, and N-As doped GeC systems were systematically studied. The results show that the single layer GeC is a direct bandgap semiconductor with the bandgap of 2.10 eV. Compared with the single layer GeC, the bandgap and work function of the doped system decrease, indicating that the required energy for electronic transition is relatively small in our doped system. Moreover, the light absorption coefficient of the doped system improves, and the absorption band edge has also undergone a red shift, effectively expanding the response range of the system to light and improving the absorption ability of the system to photons. In addition, the As doped GeC system not only exhibits impurity levels near the Fermi level, but also shows the optimal optical properties such as absorption coefficient, static dielectric function, and extinction coefficient in the low energy region. The above research can provide a theoretical basis for the preparation of relevant GeC photoelectric experiments.

Effect of Bi and Ag Doping on the Thermoelectric Property of SnTe

GAO Lei, YANG Xinyue, LI Wenhao, WANG Jianing, LIU Ruixiu, ZHENG Shuqi

2024, 53(3):  526-533. 

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SnTe has been widely studied as an alternative to PbTe because of its similar crystal structure and band structure to PbTe, the thermoelectric material with the best performance in the middle temperature region. Reducing the energy difference between heavy and valence bands and enlarging the band gap of SnTe are effective means to optimize the thermoelectric performance of SnTe. In this paper, by co-doping SnTe with Bi and Ag, the energy difference between heavy and valence bands is effectively reduced, the band gap is obviously increased, and the Sn_1-2xBi_xAg_xTe(x=0,0.01,0.02,0.03,0.04) samples with improved electric transport properties are obtained. Compared with undoped SnTe, the power factor of Sn_1-2xBi_xAg_xTe samples doped x=0.03 and 0.04 is significantly improved, and the maximum power factor of Sn_0.94Bi_0.03Ag_0.03Te samples is 15.34 μW·cm^-1·K^-2, which is 12.9% higher than undoped SnTe. The maximum power factor of Sn_0.92Bi_0.04Ag_0.04Te sample is 14.53 μW·cm^-1·K^-2. At the same time, Bi and Ag doping decreased the thermal conductivity of SnTe. In this study, the total thermal conductivity of Sn_0.92Bi_0.04Ag_0.04Te samples is significantly lower than that of undoped SnTe, and the thermal conductivity of all samples gradually decreases with the increase of temperature. At 823 K, the total thermal conductivity of Sn_0.92Bi_0.04Ag_0.04Te sample decreases to 3.073 W·m^-1·K^-1, and its ZT value increases to 0.387. It can be seen that the co-doping of Bi and Ag is an effective strategy to improve the thermoelectric performance of SnTe.

Construction and Electrochemical Properties of Co/Ni Coordination Polymer Based on Flexible Phenyldiacetate

LIN Taohai, ZHANG Jun, GE Qing, ZHANG Gangqiang, ZHANG Meili

2024, 53(3):  534-540. 

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Two coordination polymers ([Co(tib)(mpda)(H₂O)₂]·H₂O, [Ni(tib)(mpda)(H₂O)₂]·H₂O) were synthesized based on flexible phenyldiacetic acid, and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis and X-ray single crystal diffraction. In the structure of [Ni(tib)(mpda)(H₂O)₂]·H₂O, the tib ligands coordinate as three nodes with Co(II) ions to form a 2D grid plane; cis-mpda ligands are attached to the 2D grid face as end-bases; through the O—H…O interaction between the mpda virgin carboxyl O and the coordinated water molecule (bond length of O1…O3 is 0.262 4 nm, ∠O5—H5A…O2=155.41°), a three-dimensional supramolecular network structure is formed. Two coordination polymers belong to the heterogeneous crystal structure. The specific surface areas of the two coordination polymers are 54 and 58 m²/g, respectively. [Ni(tib)(mpda)(H₂O)₂]·H₂O has a complete cyclic voltammetric curve (reduction and oxidation potentials are 0.205 and 0.563 V, respectively) and good scanning rate.

Study on Electronic Structure and Magnetic Property of MnGa Binary Alloy under Isostatic Pressure

ZHANG Feipeng, LU Qingmei, LIU Weiqiang, ZHANG Dongtao, YUE Ming

2024, 53(3):  541-550. 

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In order to study the electronic structure and magnetic properties of the non-rare earth based MnGa binary alloys under isostatic pressure, the crystal structure, formation, spin electronic structure as well as magnetic property of the tetragonal MnGa alloy under isostatic pressure of 500 MPa were systematically studied based on density functional theory calculation method. The results show that the tetragonal MnGa alloy can be formed easier, however the compressibility is anisotropic under the isostatic pressure of 500 MPa. The distances between heterogeneous species are smaller than that between the homogeneous species. The band structures are anisotropic and metallic. The Mn d states form higher net magnetic moment than that of the Ga d states in the MnGa alloy, and the Mn d states contribute to systematic remanent magnetism. The tetragonal MnGa alloy presents weak ferrimagnetism, its net magnetic moment decreases under 500 MPa.