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defect structure and dielectric properties of Mn-doped X8R BaTiO3-based ceramics with high permittivity: Experiments and first-principle calculations

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CERAMICS INTERNATIONAL 2023年第11期49卷 16514-16523页

作者： Xue, Keying Xie, Jialing Wang, Menglong Li, Lingxia Tianjin Univ Sch Microelect Tianjin 300072 Peoples R China Tianjin Univ Tianjin Key Lab Imaging & Sensing Microelect Techn Tianjin 300072 Peoples R China Tianjin Univ Key Lab Adv Ceram & Machining Technol Minist Educ Tianjin 300072 Peoples R China

The comprehensive control of dielectric properties and temperature stability is the focus of BaTiO3-based ceramics with non-reducibility. For this purpose, BaTiO3-0.02MgO-0.02Y(2)O(3)-0.04CaZrO(3)-xMnO(2)(x = 0, 0.005, 0.01 and 0.015) ceramics were prepared by the solid-state method and sintered in a reducing atmosphere. When x = 1.5 mol%, high dielectric constant (epsilon(r) similar to 3644), large insulation resistivity (rho(v) similar to 2.07 x 10(11) ohm cm), and low dielectric loss (tan delta similar to 0.011) were obtained in ceramics, which demonstrated the superior potential of current studies. The effects of multivalent Mn-ion doping on the phase transition, dielectric characteristics, and defect polarization were systematically investigated based on the experimental results and first-principle calculations. The change of dielectric properties was related to the formation of new defect dipoles ([Mn-Ti '-Y-Ba(center dot)] and[Mn-Ti ''-2Y(Ba)(center dot)]). According to the first-principle calculations, the deformation of ceramic structures and the nonuniform distribution of electron density lead to the weakening of chemical bonds and the enhancement of carrier transitions. The interfacial polarization associated with the long-range hopping of oxygen vacancies is the main source of high dielectric constant for Mn15 ceramic samples. Furthermore, all ceramics showed excellent temperature stability and satisfied the EIA X8R standard (-55 degrees C-150 degrees C, Delta C/C-25 degrees C <= +/- 15%), which can be explained by the "core-shell" structure. The effect of internal defect structure on polarization mode presented in this work can be applied to the study of BaTiO3-based dielectric ceramics. The results have excellent application potential in the BME-MLCC industry.

关键词： Temperature stability High dielectric constant defect structure Polarization mode BaTiO3

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Research of the defect structure and colouring mechanism of black lithium tantalate wafers

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OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS 2024年第3-4期18卷 161-168页

作者： Xu, Qingyan Si, Jiashun Liang, Shuaijie Zhang, Yan Huang, Yan Ma, Lingling Hai, Liang Zhang, Xuefeng Wang, Mengfan Zhang, Huan Xiao, Xuefeng North Minzu Univ Coll Elect & Informat Engn Yinchuan 750021 Peoples R China North Minzu Univ Key Lab Phys & Photoelect Informat Funct Mat Sci & Yinchuan 750021 Peoples R China North Minzu Univ Microelect & Solid State Elect Device Res Ctr Yinchuan 750021 Peoples R China Ningxia Ju Jing Yuan Crystal Technol Co Ltd Shizuishan 753000 Peoples R China Zhengzhou Univ Sch Mat Sci & Engn Zhengzhou 450001 Peoples R China

In this work, a chemical reduction method has been used to prepare black lithium tantalate (BLT) wafers. The defect structure and chromogenic mechanism of BLT wafers were investigated. It was found that the reduction process results in the reduction of a large amount of Ta5+ to Ta4+, and a small percentage of low valence Ta3+/2+ ions to Ta4+ or Ta5+ on the surface of lithium tantalate wafers. At the same time, it produced a large number of O vacancies. The O vacancies and structural distortion of TaO6 were the main reasons for the blackening of lithium tantalate wafers.

关键词： Black lithium tantalate defect structure Colouring mechanism O vacancies

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Growth of heavily doped LiNbO3:Ce crystals, their physicochemical and optical characteristics and defect structure

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JOURNAL OF SOLID STATE CHEMISTRY 2024年 332卷

作者： Palatnikov, M. N. Tokko, O. V. Kadetova, A. V. Petrova, S. V. Teplyakova, N. A. Palatnikova, O. V. Russian Acad Sci Tananaev Inst Chem Subdiv Fed Res Ctr Kola Sci Ctr Murmansk Oblast Russia Petrozavodsk State Univ Petrozavodsk Russia

A series of LiNbO3:Ce crystals was grown using the Czochralski method in a wide range of dopant concentrations ([Ce] = 0.55-2.41 wt% in the melt). The physicochemical characteristics of the crystal-melt Li2O-Nb2O5-CeO2 system during the growth of the LiNbO3:Ce crystals have been studied. Optical characteristics and defect structure of the crystals were studied using the methods of photoinduced light scattering (PILS), laser conoscopy, optical spectroscopy and XRD. In the range of dopant concentrations in the crystal [Ce] approximate to 0.8-0.88 wt%, pronounced threshold effects have been detected in the LiNbO3:Ce crystals. It has been shown that LiNbO3:Ce crystals with a high dopant concentration can be used as "black" lithium niobate - a temperature -independent acoustoelectronic material free from pyroelectric effects.

关键词： Cerium-doped lithium niobate crystal Threshold effects defect structure Macro and micro-domain structure

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Effect of zirconium content on defect structure and optical uniformity of dysprosium-doped lithium niobate crystals

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RADIATION EFFECTS AND defectS IN SOLIDS 2024年第3-4期179卷 537-547页

作者： Dai, Li Zhang, Lin Wang, Houliang Lai, Ning Harbin Univ Sci & Technol Sch Mat Sci & Chem Engn Harbin Peoples R China

Four Zr: Dy: LiNbO3 crystals doped with different concentrations of Zr4+ (0, 1, 2, 4, mol%) have been grown by Czochraski technique. The effect of doping concentration of Zr4+ ions on the actual concentration of Zr4+ and Dy3+ ions in doped crystal was studied by the inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results of X-ray diffraction and ultraviolet absorption spectroscopy showed that the Zr: Dy: LiNbO3 crystal still maintained the original lattice structure of the pure lithium niobate crystal, and the doped ions entered the crystal by preferential substitution of Nb-Li(4+), and doped ions entered the crystal When Nb-Li(4+) is completely replaced, ions are doped to replace the normal Nb and Li positions into the crystal. The lattice constant with the increase of Zr content shows a trend of first becoming larger and then smaller. Finally, the optical uniformity of Zr4+ doped concentration on Zr: Dy: LiNbO3 crystals was studied by birefringence gradient method. The results showed that with the increase of Zr4+ ion doping concentration, the crystal optical uniformity of Zr: Dy: LiNbO3 gradually increased, and the optical uniformity reached the highest when doped at a concentration of 4 mol%. Based on the Li-site vacancy model, the experimental results are discussed in detail.

关键词： Zr: Dy: LiNbO3 crystal defect structure optical uniformity UV-VIS-spectroscopy

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High- entropy engineering with regulated defect structure and electron interaction tuning active sites for trifunctional electrocatalysis

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PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2024年第13期121卷 e2313239121-e2313239121页

作者： Zou, Xiaoxiao Xie, Jiyang Mei, Zhiyuan Jing, Qi Sheng, Xuelin Zhang, Conghui Yang, Yongxin Sun, Mengjiao Ren, Futong Wang, Lilian He, Tianwei Kong, Youchao Guo, Hong Yunnan Univ Int Joint Res Ctr Adv Energy Mat Yunnan Prov Sch Mat & Energy Yunnan Key Lab Carbon Neutral & Green Low carbon T Kunming 650091 Peoples R China Yancheng Teachers Univ Dept Phys & Elect Engn Yancheng 224002 Peoples R China Southwest United Grad Sch Kunming 650091 Peoples R China

High- entropy alloy nanoparticles (HEANs) possessing regulated defect structure and electron interaction exhibit a guideline for constructing multifunctional catalysts. However, the microstructure-activity relationship between active sites of HEANs for multifunctional electrocatalysts is rarely reported. In this work, HEANs distributed on multi- walled carbon nanotubes (HEAN/CNT) are prepared by Joule heating as an example to explain the mechanism of trifunctional electrocatalysis for oxygen reduction, oxygen evolution, and hydrogen evolution reaction. HEAN/CNT excels with unmatched stability, maintaining a 0.8V voltage window for 220 h in zinc-air batteries. Even after 20 h of water electrolysis, its performance remains undiminished, highlighting exceptional endurance and reliability. Moreover, the intrinsic characteristics of the defect structure and electron interaction for HEAN/CNT are investigated in detail. The electrocatalytic mechanism of trifunctional electrocatalysis of HEAN/CNT under different conditions is identified by in situ monitoring and theoretical calculation. Meanwhile, the electron interaction and adaptive regulation of active sites in the trifunctional electrocatalysis of HEANs were further verified by density functional theory. These findings could provide unique ideas for designing inexpensive multifunctional high- entropy electrocatalysts.

关键词： high- entropy alloy nanoparticles trifunctional electrocatalysis defect structure electron interaction

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Investigation of defect structure and Optical Properties of Sc: Yb: Ho: LiNbO3 Crystals with Different [Li]/[Nb] Ratios

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INTEGRATED FERROELECTRICS 2023年第1期237卷 58-66页

作者： Dai, Li Lai, Ning Wang, Houliang Zhang, Lin Harbin Univ Sci & Technol Sch Mat Sci & Chem Engn Harbin Peoples R China

Sc: Yb: Ho: LiNbO3 crystals with various [Li]/[Nb] ratios (0.85, 0.94, 1.05, 1.20 and 1.38) were grown by Czochralski method. In this report, the effect of the [Li]/[Nb] ratio dependence of the doped element concentration and segregation coefficient was studied using an inductive coupled plasma-atomic emission spectrometer (ICP-AES). It was found that the change of the [Li]/[Nb] ratio will affect the concentration and the occupancy of the doped ions in the crystal. The structures of the crystals with different [Li]/[Nb] ratios are analyzed using X-ray diffraction patterns (XRD). It was found that doping elements do not change the crystal structure, and the crystal has the least defects when the [Li]/[Nb] ratio is 1.20. The optical uniformity of crystals was measured by birefringence gradient method. The results show that the optical uniformity of the crystal is significantly enhanced as the [Li]/[Nb] ratio increases.

关键词： Sc: Yb: Ho: LiNbO3 crystals defect structure segregation coefficient optical homogeneity

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The role of defect structure and residual stress on fatigue failure mechanisms of Ti-6Al-4V manufactured via laser powder bed fusion: Effect of process parameters and geometrical factors

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JOURNAL OF MANUFACTURING PROCESSES 2023年 102卷 549-563页

作者： Hosseini, Seyed Mehrab Vaghefi, Ehsan Mirkoohi, Elham Auburn Univ Dept Mech Engn Auburn AL 36849 USA

Undoubtedly, one of the greatest revolutions in the last few decades has been the paradigm shift in design and manufacturing of components using additive manufacturing (AM) technologies. Despite the numerous benefits of metal AM, the presence of volumetric defects and the development of residual stress during manufacturing pose significant obstacles for producing load-bearing components critical for missions. Laser powder bed fusion (LPBF) has many process parameters, each potentially affecting volumetric defects and residual stress, which may lead to varying fatigue performance. In this paper, we comprehensively investigate the criticality of volumetric defects and residual stress on fatigue properties of AMed Ti-6Al-4V. Using X-ray computed tomography (XCT) and X-ray diffraction (XRD), we characterized volumetric defects and measured residual stress of the specimens, respectively. We performed extensive statistical analysis to correlate XCT, residual stress, and fatigue data, allowing us to identify the factors impacting components' fatigue life. Our observations indicate that residual surface stress plays a crucial role in the fatigue performance of components in the absence of defects at the "critical location". Furthermore, we found that the pore location has a more significant impact than the defect size on fatigue fracture.

关键词： defect structure Residual stress Fatigue performance Ti-6Al-4V

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Colossal permittivity in Ta-doped SrTiO3 ceramics induced by interface effects and defect structure: An experimental and theoretical study

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CERAMICS INTERNATIONAL 2023年第12期49卷 20388-20397页

作者： Xue, Keying Li, Lingxia Tianjin Univ Sch Microelect Tianjin 300072 Peoples R China Tianjin Univ Tianjin Key Lab Imaging & Sensing Microelect Techn Tianjin 300072 Peoples R China Tianjin Univ Minist Educ Key Lab Adv Ceram & Machining Technol Tianjin 300072 Peoples R China

The lack of systematic research on the phase structure, defect structure, and polarization mechanism hinders the full comprehension of the colossal permittivity (CP) behavior for SrTiO3-based ceramics. For this purpose, Ta-doped SrTiO3-based ceramics were synthesized in an N-2 atmosphere with a traditional method. When the appropriate amount of Ta was doped, colossal permittivity (epsilon(r)similar to 62505), low dielectric loss (tan delta similar to 0.07), as well as excellent temperature stability (-70 degrees C-180 degrees C, Delta C/C25 degrees C <= +/- 15%) were obtained in the Sr0.996Ta0.004TiO3 ceramic. The relationship between Ta doping, polarization mechanism, and dielectric performance was sys-tematically researched according to experimental analysis and theoretical calculations. The first-principle cal-culations indicate that the Ta5+ ion prefers to replace the Sr-site. The defect dipoles and oxygen vacancies formed by heterogeneous-ion doping play an active role in regulating the dielectric performance of ceramics. In addition, the interface barrier layer capacitance (IBLC) effect associated with semi-conductive grains and insulating grain boundaries is the primary origin of colossal permittivity for Sr1-xTaxTiO3 ceramics. The polarization mechanism and defect structure proposed in the study can be extended to the research of SrTiO3 CP ceramics. The results have a good development prospect in colossal permittivity (CP) materials.

关键词： Colossal permittivity defect structure Polarization mechanism SrTiO 3-based ceramics Dielectric properties

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A novelty strategy induced pinning effect and defect structure in Ni-rich layered cathodes towards boosting its electrochemical performance

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Journal of Energy Chemistry 2022年第9期31卷 570-580,I0016页

作者： Zhouliang Tan Yunjiao Li Xiaoming Xi Shijie Jiang Xiaohui Li Xingjie Shen Panpan Zhang Zhenjiang He Junchao Zheng School of Metallurgy and Environment Central South UniversityChangsha 410083HunanChina Engineering Research Center of the Ministry of Education for Advanced Battery Materials Central South UniversityChangsha 410083HunanChina Changsha Research Institute of Mining and Metallurgy Changsha 410083HunanChina Office of Laboratory and Equipment Management Xinjiang UniversityUrumqi 830000XinjiangChina

Layered Ni-rich transition metal oxide is treated as the most promising alternative cathode due to their high-capacity and flexible ***,the severe lattice strain and slow Li-ion migration kinetics severely restrict their practical ***,a novelty strategy induced pinning effect and defect structure in layered Ni-rich transition metal oxide cathodes is proposed via a facile cation(iron ion)/anion(polyanion)co-doping ***,the effects of pinning effect and defect structure on element valence state,crystal structure,morphology,lattice strain,and electrochemical performance during lithiation/delithiation are systematically *** detailed characterizations(soft X-ray absorption spectroscopy(sXAS),in-situ X-ray diffraction(XRD),etc.)and density functional theory(DFT)calculation demonstrate that the pinning effects built-in LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)materials by the dual-site occupation of iron ions on lithium and transition metal sites effectively alleviate the abrupt lattice strain caused by an unfavorable phase transition and the subsequent induction of defect structures in the Li layer can greatly reduce the lithium-ion diffusion ***,the modified LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)exhibits a high-capacity of 206.5 mAh g^(-1)and remarkably enhanced capacity retention of 93.9%after 100 cycles,far superior to~14.1%of the pristine ***,an excellent discharge capacity of 180.1 mAh g^(-1)at 10 C rate is maintained,illustrating its remarkable rate *** work reports a pinning effect and defect engineering method to suppress the lattice strain and alleviate lithium-ion kinetic barriers in the Ni-rich layered cathodes,providing a roadmap for understanding the fundamental mechanism of an intrinsic activity modulation and structural design of layered cathode materials.

关键词： Ni-rich layered cathode Pinning effect defect structure Lattice strain Lithium-ion kinetic

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Mixed (Sr1-xCax)(33)Bi24Al48O141 fullerenoids: the defect structure analysed by (S)TEM techniques

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INTERNATIONAL JOURNAL OF MATERIALS RESEARCH 2022年第7期97卷 978-984页

作者： Lebedev, Oleg, I Bals, Sara Van Tendeloo, Gustaaf Snoeck, G. Etienne Retoux, Richard Boudin, Sophie Hervieu, Maryvonne Univ Antwerp EMAT Groenenborgerlaan 171 B-2020 Antwerp Belgium CEMES CNRS Toulouse France Lab CRISMAT Caen France

(Sr1-xCax)(33)Bi24+delta Al48O141+3 delta/2 fullerenoid solid solutions have been synthesized and the effect of partial substitution of Sr by Ca has been characterized by (scanning) transmission electron microscopy, applying different imaging methods. Most of the defects commonly observed in face centered cubic compounds, have also been observed in (Sr1-xCax)(33)Bi24+delta Al48O141+3 delta/2. Based on purely geometrical and topological models, structural presentations for the coherent twin boundaries and stacking faults have been constructed on the basis of complex spherical "Al84O210" units. The results are compared to defects observed in the crystallite fullerite C-60.

关键词： Fullerenoid oxide defect structure Electron microscopy Z-contrast

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