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Discovery of superhard materials via CALYPSO methodology

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Chinese Physics B 2019年第10期28卷 10-21页

作者： Shuangshuang Zhang julong he Zhisheng Zhao Dongli Yu Yongjun Tian Center for High Pressure Science (CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan University

The study of superhard materials plays a critical role in modern industrial applications due to their widespread applications as cutting tools, abrasives, exploitation drills, and coatings. The search for new superhard materials with superior performance remains a hot topic and is mainly considered as two classes of materials:(i) the light-element compounds in the B-C-N-O(-Si) system with strong and short covalent bonds, and(ii) the transition-element light-element compounds with strong covalent bonds frameworks and high valence electron density. In this paper, we review the recent achievements in the prediction of superhard materials mostly using the advanced CALYPSO methodology. A number of novel, superhard crystals of light-element compounds and transition-metal borides, carbides, and nitrides have been theoretically identified and some of them account well for the experimentally mysterious phases. To design superhard materials via CALYPSO methodology is independent of any known structural and experimental data, resulting in many remarkable structures accelerating the development of new superhard materials.

关键词： CALYPSO superhard materials crystal structure prediction

Fibre Metallurgy Characteristic of Short Cast Iron Fibre and Its Applications for Diamond Wheel

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Journal of Materials Science & Technology 1994年第4期10卷 246-250页

作者： Shizhen CheN Dongli YU julong he Yongjun TIAN and Dongchun LI (Yanshan University, Qinhuangdao City, 066004, China) Yanshan Univ Qinhuangdao China

A kind of diamond grinding wheel bonded by short cast iron fibres has been developed. ln comparison with high quality bronze bonded diamond grinding wheel. the new wheel was more suitable to grind hard and brittle materials like ceramics. For Si3N4, the grinding efficiency has been raised two times and the grinding ratio five times

关键词： Cast Fibre Metallurgy Characteristic of Short Cast Iron Fibre and Its Applications for Diamond Wheel MPa

Nanocrystalline high-entropy hexaboride ceramics enable remarkable performance as thermionic emission cathodes

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Fundamental Research 2023年第6期3卷 979-987页

作者： Mengdong Ma Xinyu Yang Hong Meng Zhisheng Zhao julong he Yanhui Chu School of Materials Science and Engineering South China University of TechnologyGuangzhou 510641China Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdao 066004China School of Materials Science and Engineering Hefei University of TechnologyHefei 230009China

The development of high-entropy borides with combined structural and functional performance holds untold scientific and technological potential,yet relevant studies have been rarely *** this work,we report nanocrystalline(La_(0.25)Ce_(0.25)Nd_(0.25)Eu_(0.25))B6 high-entropy rare-earth hexaboride(heReB6-1)ceramics fabricated through the high-pressure sintering of self-synthesized nanopowders for the first *** as-fabricated samples exhibited a highly dense(96.3%)nanocrystalline(94 nm)microstructure with major(001)fiber textures and good grain boundaries without any impurities,resulting in a remarkable mechanical,electrical,and thermionic emission *** results showed that the samples possessed outstanding comprehensive mechanical properties and a high electrical resistivity from room temperature to high temperatures;these were greater than the average values of corresponding binary rare-earth hexaborides,such as a Vickers hardness of 23.4±0.6 GPa and a fracture toughness of 3.0±0.4 MPa•m^(1/2)at room *** importantly,they showed high emission current densities at elevated temperatures,which were higher than the average values of the corresponding binary rare-earth *** instance,the maximum emission current density reached 48.3 A•cm^(−2)at 1873 *** superior performance makes the nanocrystalline heReB6-1 ceramics highly suitable for potential applications in thermionic emission cathodes.

关键词： High-entropy ceramics hexaborides Nanocrystalline Mechanical properties Thermionic emission

Experimental Observation of Cubic C_3N_4 Compound in Carbon Nitride Thin Films

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Journal of Materials Science & Technology 1999年第5期15卷 480-482页

作者： Furen XIAO Dongli YU Yongjun TIAN julong he Dongchun LI and Wenkui WANG(College of Materials Science and Chemical Engineering, Yanshan University, Qinhuangdao 066004, China To whom correspondence should be addressed E-mail: fhcl@*** ) College of Materials Science and Chemical Engineering Yanshan University Qinhuangdao 066004 China

Cubic C3N4 compound in the C-N thin films on Si and NaCl substrates was prepared by ion beam sputtering of a pure graphite target with discharge gas of pure N2. X-ray photoelectron spectroscopy indicated that nitrogen atoms combined with sp2- and sp3- coordinated C atoms in the film, respectively. X-ray diffraction, selected area electron diffraction and high-resolution electron microscopy were used to identify the cubic C3N4 phase. The results reconfirm the ab initio calculations on metastable structure in C-N compounds

关键词： Thin Experimental Observation of Cubic C3N4 Compound in Carbon Nitride Thin Films Rev

Extraordinary high-temperature mechanical properties in binder-free nanopolycrystalline WC ceramic

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Journal of Materials Science & Technology 2022年第2期97卷 169-175页

作者： Hongfeng Dong Baozhong Li BoBo Liu Yang Zhang Lei Sun Kun Luo Yingju Wu Mengdong Ma Bing Liu Wentao Hu julong he Dongli Yu Bo Xu Zhisheng Zhao Yongjun Tian Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdao 066004China School of Materials Science and Engineering Shaanxi University of TechnologyHanzhong 723001China

From the perspective of high-temperature applications,materials with excellent high-temperature mechanical properties are always *** present work demonstrates that the binder-free nanopolycrystalline WC ceramic with an average grain size of 103 nm obtained by high-pressure and hightemperature sintering exhibits excellent mechanical properties at both room temperature and high temperature up to 1000℃.Specifically,the binder-free nanopolycrystalline WC ceramic still maintains a considerably high Vicker hardness H_(V)of 23.4 GPa at 1000℃,which is only 22%lower than the room temperature H_(V).This outstanding thermo-mechanical stability is superior to that of typical technical ceramics,***,Si_(3)N_(4),Al_(2)O_(3),*** grains with many dislocations,numerous low-energy,highly stableΣ2 grain boundaries,and a relatively low thermal expansion coefficient,are responsible for the observed outstanding high-temperature mechanical properties.

关键词： Binder-free nanopolycrystalline WC High-pressure and high-temperature synthesis High-temperature mechanical properties Dislocation Σ2 Grain boundary

Novel Boron Nitride Polymorphs with Graphite-Diamond Hybrid Structure

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Chinese Physics Letters 2022年第3期39卷 36-43页

作者： Kun Luo Baozhong Li Lei Sun Yingju Wu Yanfeng Ge Bing Liu julong he Bo Xu Zhisheng Zhao Yongjun Tian Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdao 066004China Key Laboratory for Microstructural Material Physics of hebei Province School of ScienceYanshan UniversityQinhuangdao 066004China

Both boron nitride(BN)and carbon(C)have sp,sp^(2)and sp^(3)hybridization modes,thus resulting in a variety of BN and C polymorphs with similar structures,such as hexagonal BN(hBN)and graphite,cubic BN(cBN)and ***,five types of BN polymorph structures are proposed theoretically,inspired by the graphite-diamond hybrid structures discovered in a recent *** BN polymorphs with graphite-diamond hybrid structures possess excellent mechanical properties with combined high hardness and high ductility,and also exhibit various electronic properties such as semi-conductivity,semi-metallicity,and even one-and two-dimensional conductivity,differing from known insulators hBN and *** simulated diffraction patterns of these BN hybrid structures could account for the unsolved diffraction patterns of intermediate products composed of so-called“compressed hBN”and diamond-like BN,caused by phase transitions in previous ***,this work provides a theoretical basis for the presence of these types of hybrid materials during phase transitions between graphite-like and diamond-like BN polymorphs.

关键词： ductility conductivity Diamond

Enhanced thermoelectric performance of Na-doped Pb Te synthesized under high pressure

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Science China Materials 2018年第9期61卷 1218-1224页

作者： Bowen Cai Jianghua Li Hao Sun Long Zhang Bo Xu Wentao Hu Dongli Yu julong he Zhisheng Zhao Zhongyuan Liu Yongjun Tian State Key Laboratory of Metastable Materials Science and Technology Yanshan UniversityQinhuangdao 066004China

Despite an effective p-type dopant for PbTe, the low solubility of Na limits the fully optimization of thermoelectric properties of Na-doped PbTe. In this work, Na-doped PbTe was synthesized under high pressure. The formation of the desired rocksalt phase with substantially increased Na content leads to a high carrier concentration of 3.2×10^20 cm^-3 for Na0.03Pb0.97Te. Moreover, dense in-grain dislocations are identified from the microstructure analysis. Benefited from the improved power factor and greatly suppressed lattice thermal conductivity, the maximal ZT of 1.7 is achieved in the optimal Na0.03Pb0.97Te. Current work thus designates the advantage of high pressure in synthesizing PbTe-based thermoelectric materials.

关键词： lead telluride high pressure synthesis carrier concentration dislocation

The rise of plastic deformation in boron nitride ceramics

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Science China Materials 2021年第1期64卷 46-51页

作者： Yingju Wu Yang Zhang Shuangshuang Zhang Xiaoyu Wang Zitai Liang Wentao Hu Zhisheng Zhao julong he Dongli Yu Bo Xu Zhongyuan Liu Yongjun Tian Center for High Pressure Science(CHiPS) State Key Laboratory of Metastable Materials Science and TechnologyYanshan UniversityQinhuangdao066004China Key Laboratory for Microstructural Material Physics of hebei Province Yanshan UniversityQinhuangdao066004China

Ceramics are bonded by ionic or covalent bonds,with very limited slip systems for dislocation nucleation and movement[1].The poor deformability and natural brittleness are the major drawbacks of ceramics,especially when compared with *** stress,ceramics tend to fracture before noticeable plastic deformation takes *** occur and propagate rapidly in ceramics subjected to stress much lower than the theoretical strength[2].As a result,ceramics can only endure very small strains(he toughness even *** to the lack of significant plastic deformation capacity for ceramic materials,the catastrophic failures without warning are easy to happen under stress which critically increases the unreliability of ceramics in the applications as structural materials.

关键词：氮化硼陶瓷陶瓷材料刚性结构择优取向压缩强度纳米薄片随机取向原子层

Impact of Lattice Volume on the Band Gap Broadening of Isovalent S-Doped CuInSe_2

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Journal of Semiconductors 2008年第10期29卷 1883-1888页

作者：陈翔赵宇军姚若河何巨龙华南理工大学物理科学与技术学院广州510640 燕山大学材料科学与工程技术学院秦皇岛066004

The electronic structure of pure and S-doped chalcopyrite CulnSe2 is investigated using a first-principles pseudopotential method in the generalized gradient approximation. The calculation indicates that the band gap of CulnSe2 broadens as S-doping concentration increases. We find that the decreased lattice volume due to isovalent S-doping in CulnSe2 has a significant impact on the band gap broadening phenomena. This physical insight is further discussed with the study of the electronic structure and bond length changes.

关键词： first-principles calculation CulnSe2 band gap broadening