Table of Content

15 January 2022, Volume 51 Issue 1

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Invited

Research Progress on the Growth of SiC Single Crystal via High Temperature Solution Growth Method

WANG Guobin, LI Hui, SHENG Da, WANG Wenjun, CHEN Xiaolong

2022, 51(1):  3-20. 

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As a third-generation semiconductor material, silicon carbide (SiC) has excellent properties such as wide bandgap, high thermal conductivity, high saturation electron drift velocity, strong radiation resistance, good thermal and chemical stability, et al. It has great application potential in high temperature, high power, high frequency power electronic devices and radio frequency devices. The production of high-quality, large-size, and low-cost SiC single crystal substrates is a prerequisite for large-scale applications of SiC devices. However, the supply of SiC single crystal substrates still faces some challenges, such as high defect density, low yield and high cost. High temperature solution growth (HTSG) technique, with top seeded solution growth (TSSG) as the main technical model at present, has advantages of fabrication of SiC with low defects density, easy to enlarge diameter, and easy to obtain p-type doping. In the future, it is expected to become one of the mainstream technologies to mass produce SiC single crystals. In this paper, the development of SiC single crystal grown by TSSG is reviewed firstly. Then the principle and growth process of SiC single crystal growth by TSSG are introduced and analyzed. The research progress of TSSG for SiC single crystal growth is summarized from crystal growth thermodynamics and kinetics. The unique advantages of this technology are summarized. Finally, the future research direction and challenges of this method are given.

Research Articles

Growth and Luminescent Properties of KCaCl₃:Ce Crystals

SHEN Yiming, LI Man, YANG Chenyue, ZHU Shujun, PAN Shangke, PAN Jianguo

2022, 51(1):  21-26. 

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The single crystals of KCaCl₃:Ce doped with different mole fraction of Ce³⁺ ion concentrations(1%, 2%, 4%, 6%, 8%) were successfully grown by Bridgman method. The crystals belong to orthorhombic system, the cell parameters have been determined as: a=0.756 0 nm, b=1.048 2 nm, c=0.726 6 nm. The melting point measured by the thermogravimetric analyzer are 740 ℃. The photoluminescence spectrum, decay time, X-ray excitation emission spectrum and optical transmittance were characterized. The transmittance shows it has good optical transmittance in visible band. The photoluminescence spectra of KCaCl₃:Ce exhibit the two broad emission peaks locate at 358 nm and 378 nm, corresponding to Ce³⁺5d₁→²F_5/2 and 5d₁→²F_7/2 energy level transition; the scintillating decay time of the KCaCl₃:Ce is about 30 ns under ultraviolet excitation. Moreover, all crystals exhibit excellent X-ray liminescence properties under X-ray excitation.

Effects of Seed-Holder Shape on the Initial Growth of AlN Single Crystals by Homoepitaxial PVT Method

ZHANG Gang, FU Danyang, LI Zhe, HUANG Jiali, WANG Qikun, REN Zhongming, WU Liang

2022, 51(1):  27-34. 

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The initial temperature field and mass transport during homoepitaxial AlN growth process by the PVT method were studied by FEMAG and in-house developed convection, mass transport, supersaturation and growth rate prediction finite element modules. The influences of the seed-holder shape on the temperature field, flow field, supersaturation and growth rate were investigated in detail by numerical simulations. The simulation results show that the flow and mass transport near the seed-holder were strongly affected by the axial and radial temperature gradient near the seed deposition surface, and these temperature gradients near the seed deposition surface could be calibrated by the expansion angle θ of the seed-holder. When the angle θ of the seed-holder is 130°, the temperature gradient at seed surface is small and the polycrystalline deposition at the seed surface and seed-holder periphery can be completely prohibited, which is beneficial to grow parasitic-free, crack-free and high-quality AlN single crystals.

Microstructure and Optical-Electrical Properties of Phosphorus/Boron Co-Doped Silicon Nanocrystals

LI Dongke, CHEN Jiaming, SUN Teng, ZHAI Zhangyin, CHEN Guibin

2022, 51(1):  35-41. 

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Si/SiO₂ multilayers were fabricated by RF plasma enhanced chemical vapor deposition system, and phosphorus/boron (P/B) co-doped silicon nanocrystals (Si NCs) were obtained under the constricted crystallization of multilayers structures. Microstructures of P/B co-doped Si NCs/SiO₂ multilayers and impurities distributions were studied by Raman, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Low temperature electron paramagnetic resonance (EPR) results indicate that the non-radiative defects on Si NCs surfaces can be passivated by P and B impurities. Hall effect manifests that P and B impurities can substitutionally incorporate into Si NCs inner. Meanwhile, P impurity exhibits higher doping efficiency than B. Near-infrared photoluminescence near 1 200 nm with the wavelength compatible for optical telecommunication was detected in the small-sized P/B co-doped Si NCs. The emission intensity can be enhanced by regulating the nominal P-doping concentration. According to the time-resolved photoluminescence and EPR results, the physical mechanisms of P-doping on the radiative and non-radiative recombination processes of Si NCs were discussed, which are responsible for the enhancement of 1 200 nm photoluminescence.

Preparation of C8-BTBT Single Crystals by Solvent Vapor Annealing Assisted Micro-Spacing Sublimation

SHI Shaohui, FANG Zhenyu, WANG Hong

2022, 51(1):  42-48. 

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Organic semiconductor single crystal has excellent device performance due to its long-range ordered molecular arrangement, few defects and grain boundaries. It is considered as a candidate to realize the practicability of organic semiconductor devices. At present, researchers have developed a variety of methods that can be applied in the growth of organic single crystals. Micro-spacing sublimation is a method to prepare organic micro/nano single crystals by sublimating organic semiconductor molecules onto substrates under ambient conditions. However, when C8-BTBT was treated by this method, amorphous/polycrystalline islands instead of single crystals were obtained due to the low melting point of C8-BTBT. In this work, these amorphous/polycrystalline islands are successfully transformed into discrete single crystals by solvent vapor annealing. The morphology and structure of the obtained crystals were characterized by optical microscope, X-ray diffraction characterization and atomic force microscope. The results show that the prepared crystals have typical characteristics of single crystals.

First-Principles Study of P-Doped 6H-SiC

HUANG Sili, XIE Quan, ZHANG Qin

2022, 51(1):  49-55. 

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The electronic structure and optical properties of intrinsic 6H-SiC, P substituted for Si, C doped and P interstitial doped 6H-SiC were calculated by the first-principles pseudopotential plane wave method based on density functional theory. The results indicate that intrinsic 6H-SiC is an indirect band gap semiconductor with a band gap of 2.052 eV. The band gaps of the P substituted for Si, C doped and P interstitial doped 6H-SiC decrease to 1.787 eV, 1.446 eV and 0.075 eV, respectively. The interstitial doping band gap decreases the most. P substitutional doped 6H-SiC causes the Fermi level guide band to move and insert into the conduction band, and the 6H-SiC becomes an n-type semiconductor. One level of P interstitial doping valence band crosses into Fermi level, so a P 3p impurity level appears in the gap band, and 6H-SiC turns into p-type semiconductor. Substitutional and interstitial doping increase the real part of dielectric function of 6H-SiC, while the imaginary part of dielectric function, absorption spectrum, reflection spectrum and photoconductivity redshift. Among them, P interstitial doped 6H-SiC has the best effect. The conductivity of the material is enhanced and the utilization rate of the material in the infrared band is obviously improved by P doping. The results provide effective theoretical basis for the application of 6H-SiC in infrared photoelectric performance.

First-Principle Study on Photoelectric Properties of Mg, N Doped β-Ga₂O₃

REN Shanshan, FU Xiaoqian, ZHAO He, WANG Honggang

2022, 51(1):  56-64. 

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The structural, electronic and optical properties of Mg single doped, N single doped and different concentrations Mg-N co-doped β-Ga₂O₃ were studied via the first-principles calculation based on density function theory. This work aims to improve the effect of p-type β-Ga₂O₃doping. Five models were built including Mg single doped, N-single doped, 1 Mg-N doped, 2 Mg-N doped and 3 Mg-N doped β-Ga₂O₃. Among them, the model of 3 Mg-N doped β-Ga₂O₃ shows the most stable structure than other doped systems. In attention to, the bandgap of 3 Mg-N doped β-Ga₂O₃ material is the smallest. And occupied states contributed by N 2p and Mg 3s inhibit the formation of oxygen vacancies, which increases the concentration of holes. Thus, 3 Mg-N doped β-Ga₂O₃ system displays excellent p-type feature. Adsorption peak is obvious red-shift in 3 Mg-N doped system, and the adsorption coefficient is bigger at solar-blind region, which is ascribed to the interband electron transition from the Ga 4s, Ga 4p, Mg 3s of conduct band to O 2p, N 2p of valence band. This work will provide a theoretical guide for the study and application of p-type β-Ga₂O₃ materials.

Electronic Structure and Magnetic Properties of MnGa Alloy

ZHANG Feipeng, LU Qingmei, LI Hongfei, FANG Hui, LIU Weiqiang, ZHANG Dongtao, YUE Ming

2022, 51(1):  65-71. 

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Geometry, formation, electronic structure as well as magnetic properties of the tetragonal MnGa alloy were systematically studied by density functional theory method. The results show that the tetragonal MnGa has formation enthalpy of -4.85 eV, which is slightly higher than other compounds without d state electrons. It has conductor like band structure with the deep valance bands formed by d state electrons, they show strong localization effect. The tetragonal MnGa alloy shows obvious spin polarization. The s state electrons near Fermi energy and the p state electrons under Fermi energy have weak spin polarization, the d state electrons which form conductor band and bands below Fermi energy have strong spin polarization, they contribute to the total electronic as well as magnetic properties. The s and p state electrons of Mn have weak spin polarization, its d electrons which form conductor band and bands below Fermi energy have strongest spin polarization. The d electrons of Ga which form bands below Fermi energy have weak spin polarization. The two kinds of Ga have different spin polarization states. The tetragonal MnGa alloy has net magnetic moment, it shows weak ferrimagnetism.

First Pricinples Study on TFSI Passivating Surface of Crystal Si

WEI Lijing, MENG Zijie, GUO Jianxin

2022, 51(1):  72-76. 

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Surface passivation of crystalline silicon is the key technology of high efficiency crystalline silicon solar cells, which directly affects the performance of crystalline silicon devices. In this paper, the surface passivation of crystalline silicon (001) by a superacid bis(trifluoromethane)sulfonimide (TFSI) was studied by first principles method. It is found that the four oxygen atoms of TFSI can effectively bond with Si atoms on Si (001) surface, and the adsorption energy is -5.124 eV. The electron localization function shows that the bonding type between O atom of TFSI and Si on the surface of crystalline silicon is metal bond. The analysis of density of states and charge difference density show that the electrons on the Si surface are transferred to TFSI, which effectively reduces the electron recombination on the Si surface and improves the minority carrier lifetime of crystalline silicon. Bader charge shows that the charge of Si atoms on the surface decreases with the passivation of Si atoms on the surface of crystalline silicon by TFSI, while the charge of O atoms and S atoms in TFSI increases, which further proves the electron transfer after TFSI passivation of Si surface. This work provides data support for the first principle method to predict the passivation effect of organic strong acid passivated crystalline silicon surface.

Electronic Structure and Optical Properties of C and Ti Doped GaN by GGA+U Method

LIU Jibo, PANG Guowang, MA Lei, LIU Lizhi, WANG Xiaodong, SHI Leiqian, PAN Duoqiao, LIU Chenxi, ZHANG Lili, LEI Bocheng, ZHAO Xucai, HUANG Yineng

2022, 51(1):  77-84. 

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As an excellent semiconductor material, GaN has a wide band gap, which causes it to only absorb violet light in visible light. Therefore, how to increase the utilization rate of visible light of GaN material is a problem worthy of study. Doping is commonly used to solve this problem. Therefore, this paper uses the first-principles method to calculate the electronic structure and optical properties of the intrinsic GaN, C single-doped, Ti single-doped, and C-Ti co-doped GaN. The results show that the stability of the system after doping is all good; the volume of each system increases after doping, indicating that the introduction of impurities causes distortion of the system lattice, which helps to promote the separation of photogenerated hole-electron pairs, and further improves the photocatalytic performance of the material; the energy level of the system is split and the electronic transition is easier after the introduction of impurity elements; after doping, the main peak of the imaginary part of the dielectric function of each system moves to the low-energy region, and the absorption spectrum is red-shifted to the visible light region, and the co-doped system is in the blue-green light region, and the absorption coefficient is the largest, so it can be inferred that C-Ti co-doping will help improve the photocatalytic performance of GaN.

Effect of Volume Strain on Electronic Structure and Optical Properties of Cubic Lead Titanate

DENG Pengxing, WEN Zhiqin, MA Bo, WANG Mingze, LIU Junxiao, ZOU Zhengguang

2022, 51(1):  85-91. 

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Effect of volume strain (-11%~11%) on the structure, stability, electronic structure and optical properties of cubic paraelectric phase PbTiO₃ was calculated and analyzed via first-principles method. It is found that formation enthalpy increases and stability decreases for PbTiO₃ after volume strain. And the influence of compressive strain on the stability of PbTiO₃ is greater than that of tensile strain. When subjected to tensile strain, cubic PbTiO₃ changes from direct bandgap semiconductor to indirect bandgap semiconductor, and bandgap increase first and then decrease with the increase of strain. When compressive strain occurs, from the analysis of complex dielectric function, complex refractive index and absorption coefficient, the light absorption capacity of PbTiO₃ weakens under natural light, with fluctuations in individual wavelength. When tensile strain occurs, dielectric peak and absorption peak redshifts, and light absorption capacity of PbTiO₃ in visible light range is enhanced. Furthermore, when strain increases to 11%, the aforementioned absorption capacity outclasses than that in intrinsic cubic phase.

Transition Metal (Sc, V, Zr) Doping Effects on the Electromagnetic Properties of Ti₂N Monolayer MXene Nanosheet

ZHOU Tingyan, ZHAO Min, YANG Kun, JIA Weihai, HUANG Haishen, WU Bo

2022, 51(1):  92-97. 

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Two-dimensional MXene nanosheets have attracted much attention due to its large surface area ratio and high electron mobility. The effects of transition metal (Sc, V, Zr) doping on the electromagnetic properties of Ti₂N monolayer MXene nanosheet were studied systematically by first-principles calculation. The results show that the binding energies of all transition-metal-doped systems are negative and the structures are stable. The formation energy of the Ti₂N-Sc system is -2.242 eV, and the structure is easy to form. The magnetic moments of Ti₂N-Sc and Ti₂N-Zr systems increase after doping. In addition, the Ti₂N-Sc system retains a high spin polarization rate of 84.9%, which can be a potential candidate for spintronic applications.

Thermal Spin Transport Properties of the Li Atom Doped C₂₈ Monomolecular Device

WENG Zhulin

2022, 51(1):  98-103. 

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Thermal spin transport properties of the Li atom doped C₂₈ monomolecular device were simulated by using first-principle study combined with density functional theory. By applying a temperature field, the upper and lower spins provide transport channels for the electrons and holes in the Li doped C₂₈ monomolecular device, respectively. The thermal spin current increases with temperature increasing in the MJ₁ and MJ₃, but the thermal spin current increases then decrease with temperature increasing in the MJ₂. The spin-dependent Seebeck effect appears in the Li doped C₂₈ monomolecular device, and the negative differential resistance effect appears in the MJ₂. The physical mechanism was explained using the Fermi-Dirac distribution and spin transmission spectrum. These interesting effects suggest that the Li atom doped C₂₈ monomolecular device can be used as new spin nanodevices.

Photo-Electrical Stability of PEDOT:PSS Thin Film for Device Application

SHI Yanbin, ZHOU Yuqin, CHE Zhigang, SHANG Jiacheng, WANG Qi, LIU Fengzhen, ZHOU Yurong

2022, 51(1):  104-111. 

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PEDOT:PSS (poly 3,4-ethylenedioxythiophene-polystyrene sulfonate) film is widely used due to its good electrical conductivity, light transmittance, mechanical flexibility and solution processability. Improving the electrical conductivity and photoelectric stability of PEDOT materials is of great significance to its device applications. In this article, highly conductive PEDOT:PSS films were obtained by spin-coating method after post-treatment by sulfuric acid. The films were placed in air, oxygen, nitrogen and under sun illumination for 30 d to study their photo-electrical stability and aging mechanisms. It indicates that: sunlight is the main factor affecting the stability of photo-electrical properties of thin films, and sulfuric acid treatment removes the excessive PSS component effectively and therefore improves the stability of PEDOT:PSS films. By comparing the absorption spectrum and photoelectron spectroscopy (XPS) of the film before and after aging, it is found that, the film underwent photo-oxidation degradation during the aging process, which directly affects its photoelectrical stability.

Electromechanical Coupling Performance of (111)-Oriented 0.7PMN-0.3PT Thin Film

LI Qiang, ZHANG Peizhi, LYU Jinbin, ZHANG Qingyong, LIU Li, YE Yang

2022, 51(1):  112-119. 

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Due to its excellent physical properties, ferroelectric thin films are widely used in the fields of microelectronics, optoelectronics, and microelectromechanics. In terms of theoretical research on ferroelectric thin films, the phenomenological theory of thermodynamics can effectively predict the phase structure, polarization characteristics and electromechanical properties of ferroelectric thin films, and has been well applied in the research of (001)-oriented ferroelectric thin films. However, there are very few research reports on (111)-oriented ferroelectric thin films. Therefore, the thermodynamic potential energy function and the calculation method of electromechanical properties of the (111)-oriented thin film by transforming order parameters of the system was constructed in this paper. Based on constructed theory, the phase structure and electromechanical properties of (111)-oriented 0.7PMN-0.3PT ferroelectric thin film were studied. The results reveal that the phase structures of the (111)-oriented 0.7PMN-0.3PT ferroelectric thin film mainly have three symmetrical phases with interchangeable polarizations along the crystal axis, they are paraelectric phase PE, rhombohedral phase R and monoclinic phase M_A (or M_B). By the controling of misfit strain and external electric field, the (111)-oriented 0.7PMN-0.3PT thin film exhibits excellent electromechanical properties. At the boundary of the R-M_A phase transformation, the dielectric constants ε11, ε22, ε33 and the out-of-plane piezoelectric coefficient d33 have achieved a maximum value. With the external electric field E₃=0, 50 kV/cm, 100 kV/cm and 200 kV/cm, the peak values of the out-of-plane dielectric constant ε33 are 4 382, 2 646, 2 102 and 1 600, respectively, and the peak values of the out-of-plane piezoelectric coefficient d33 are 303.8 pm/V, 241.9 pm/V, 219.7 pm/V and 195.1 pm/V. The misfit strain and external electric field can better control the electromechanical coupling performance of the film, which provide a reference for the preparation of devices with excellent electromechanical coupling performance.

Preparation and Luminescent Properties of NaY(WO₄)₂:Sm³⁺ Powders

MENG Xiaoyan, WU Bin, LIU Qing, WANG Yi, WU Xiuping

2022, 51(1):  120-125. 

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A series of self-assembled 3D flower-like NaY_1-x(WO₄)₂:xSm³⁺(x=0, 0.005, 0.010, 0.015, 0.020, 0.025, 0.030) powders were prepared by hydrothermal method and high temperature sintering, with trisodium citrate as the anchoring agent. The phase structure, morphology, composition and luminescence properties were characterized by X-ray powder diffraction(XRD), scanning electron microscopy(SEM), infrared spectrum(FT-IR) and photoluminescence spectroscopy (PL), respectively. The results show that the synthesized samples are pure NaY(WO₄)₂ with tetragoonal scheelite structure. NaY(WO₄)₂:Sm³⁺ powders can be excited by a wavelength of 405 nm and exhibit a strong orange-red emission at 600 nm, corresponding to the ⁴G_5/2→⁶H_7/2 magnetic dipole transition of Sm³⁺. The optimum doping molar fraction of Sm³⁺ is determined to be of 0.015 based on the maximum intensity of fluorescence emission.

Synthesis, HSA Binding, and Cytotoxic Activity of Copper(Ⅱ) Complex Constructed by P-Chlorobenzoic Acid

ZENG Zhenfang, YUAN Fang, HUANG Qiuping, PANG Huayu, YANG Honglan, HUANG Qiuchan

2022, 51(1):  126-131. 

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In this paper, a copper(Ⅱ) complex [Cu(pcba)₂·(phen)(H₂O)] (pcba=p-chlorbenzoic acid, phen=1,10-phenanthroline) was synthesized. The structure of the complex belongs to triclinic, P1 space group, with a=0.790 98(2) nm,b=1.072 40(4) nm, c=1.487 19(6) nm, α=100.613(3)°, β=95.239(3)°, γ=108.334(3)°, Z=2, D_c=1.638 g·cm^-3, F(000)=582 unit cell parameters. The final R₁=0.035 9, wR₂=0.089 1. The interaction between HSA (human serum albumin) and the complex was evaluated by UV-Vis and fluorescence spectroscopy. The complex quenched the intrinsic fluorescence of HSA via static quenching with K_sv=2.35×10⁵ L·mol^-1, the quenching rate constant K_q=2.35×10¹³ L·mol^-1·s^-1, the binding constant K_a=2.14×10¹³ L·mol^-1, the binding site n=2.37. Furthermore, the proliferation inhibition effect of the complex on the cells A549, Hela and HepG2 was studied.

Process of Preparing High Sheet Resistance P-N Junction Emitter with Low Surface Phosphorus Doping Concentration

LI Wang, TANG Lu, TIAN Yahui, XUE Fei, XIN Zengnian, PAN Shengjiang

2022, 51(1):  132-138. 

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The conventional thermal diffusion process for preparing P-N junction emitter of solar cells mainly consists of two steps: pre-deposition and high temperature drive-in. In this paper, high sheet resistance (R_s) emitters with a low surface phosphorus doping concentration were prepared on p-type multicrystalline silicon wafers by introducing a constant temperature process after the high temperature drive-in step. The influence of constant temperature on the R_s and phosphorus atom doping profile of P-N junction emitter was investigated. The results show that the R_s of the P-N junction with a certain constant temperature treatment can increase reversely. Correspondingly, the doping profiles tested by secondary ion mass spectrometry (SIMS) indicate that the phosphorus doping concentration at the surface of silicon was reduced when the constant thermal treatment at temperatures of 650 ℃ to 750 ℃ was carried out after the high temperature drive-in step. Compared with the conventional diffusion process, the R_s of the P-N junction with a constant temperature treatment at 700 ℃ for 15 min increased by about 3.2 Ω/□, and the conversion efficiency E_ff of the corresponding solar cells increases to 18.69%, which is higher by 0.23% than that of the Baseline.

Hydrothermal Synthesis and Visible Light Photocatalytic Properties of Self-Doped SnO₂ Microspheres

LIU Quan, ZHAN Hongquan, YUAN Menglei, LI Fu, XIE Zhipeng, WANG Chang'an

2022, 51(1):  139-147. 

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In this study, the microspheres assembled from SnO₂ nanocrystals with abundant oxygen vacancies were synthesized by hydrothermal method using citric acid as a chelating agent and controlling the molar ratio of Sn⁴⁺/Sn²⁺. The SnO₂ nano-microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectroscopy. The results show that under the acidic hydrothermal conditions and the chelating effect of citric acid, the tin dioxide nanocrystals aggregate to form microspheres; at a Sn⁴⁺/Sn²⁺ molar ratio of 3:7, the size of the microspheres is the smallest and the overall dispersion is good. The presence of the oxygen vacancies will extend the light absorption range to visible light; thus, the sample shows a strong visible light catalytic efficiency and complete degradation of methyl orange within 8 min.

Preparation and Properties of the Near Zero Thermal Expansion of Zr_0.5Hf_0.5V_1.4P_0.6O₇

WANG Junping, CHEN Qingdong, MU Wenying, LIANG Erjun

2022, 51(1):  148-153. 

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Near zero expansion oxide functional ceramics Zr_0.5Hf_0.5V_1.4P_0.6O₇ was synthesized by the traditional solid-state method and then the thermal expansion properties of the synthesized samples were explored.X-ray diffraction(XRD), Raman spectra and thermal dilatometry were used to investigate the coefficient of thermal expansion (CTE), isotropy and phase transition of Zr_0.5Hf_0.5V_1.4P_0.6O₇.Hf⁴⁺/P⁵⁺ double ion doping results in the material has smaller coefficient of thermal expansion. The investigation results show that the samples are single cubic phase with the space group of Pa3 in the crystal structure. The linear expansion coefficient of Zr_0.5Hf_0.5V_1.4P_0.6O₇ is calculated to be -1.56×10^-6 K^-1 in the temperature range from 334 K to 673 K and has near-zero thermal expansion characteristic in a wide temperature range. Due to the influence of the internal microstructure of the solid solution, there is a certain gap between the expansion test results and the X-ray diffraction results at variable temperature. The near zero thermal expansion (NZTE) property of Zr_0.5Hf_0.5V_1.4P_0.6O₇ provides a basis for the synthesis of materials with controllable expansion coefficient of negative thermal expansion materials.

Reviews

Strain Tuning of Multiferroic Materials

YUE Wenfeng, YU Liang, GUO Quansheng, JIA Tingting, YU Shuhui

2022, 51(1):  154-169. 

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The original definition of multiferroics is that one owns two or three “ferro” properties, such as ferroelectricity, ferroelasticity, and ferromagnetism. Furthermore, novel effects would be generated by the cross-coupling effect among various orders of multiferroic materials, and it has a broad application prospect in electronic information, sensing, storage, wireless network and other fields. At present, researchers are still focus on the multiferroic materials with strong magnetoelectric coupling effect at room temperature. However, the realization and application of devices based on multiferroics are still on the way. Strain engineering is an effective way that can influence the physical properties of multiferroic materials. The physical properties of materials such as electricity, magnetism, and photoacoustic could be influenced by strain engineering through the interaction of lattice with electrons, spins, and orbits. Tuning the structural and physical properties of ferroelectric thin films by strain has been paid extensive attention. Through investigating the research of strain engineering in multiferroic materials in this paper, herein, the strain engineering in multiferroics are summarized and effect of strain engineering on the physical properties of multiferroics is reviewed. It is prospected that the current work may provide research ideas for the investigation and development of multiferroic materials.

Research Progress of Kaolinite-Based Composites in Photocatalysis Application

ZHAO Yunpu, CHENG Hongfei, CAO Zhou, JIA Yuefa

2022, 51(1):  170-184. 

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Environmental pollution and energy shortage have become major problems that need to be solved urgently in today's society. The photocatalytic treatment technology of kaolinite-based composites has attracted much attention because of its green environmental protection, economic safety, and no secondary pollution. In view of the current research status of kaolinite in the field of photocatalysis, the unique structural characteristics of kaolinite layered silicate and its application advantages in the field of photocatalysis are introduced in this paper, and the main types, basic characteristics, synthesis methods, modification processes, photocatalytic characteristics and application progress and advantages of kaolinite-based photocatalytic materials are summarized. Finally, the key research directions for the application of kaolinite-based composite materials in the field of photocatalysis are proposed. In order to obtain a kaolinite-based photocatalytic composite material with simple preparation process, excellent photocatalytic performance, easy access to raw materials and no environmental pollution, fundamentally solve the problem of environmental pollution and alleviate the crisis of energy shortage.