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Ferroelectricity survives in the sub-nanometer scale

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Science China Materials 2023年第5期66卷 2105-2106页

作者： Yiqian Liu yuan-hua lin State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

Ultrathin materials with maintained functionalities are the prerequisites for the device miniaturization and *** materials are key ingredients in nonvolatile memories as information storage media and in field-effect transistors as gate dielectrics[1],and therefore their thickness scaling enables the high-capacity and energy-efficient ***,the longstanding problem for ultrathin ferroelectrics is that the strong depolarizing field can cancel ferroelectricity[2].In traditional barium titanates,the ultrathin film turns paraelectric without spontaneous polarizations[2,3].Moreover,realizing switchable ferroelectric behaviors is even more challenging because of the unsuppressed leakage *** recent years,although some studies have demonstrated that ferroelectricity can be stabilized in several nanometers in perovskites and fluorites[4-6],there still lacks direct evidence to confirm that ultrathin ferroelectrics have macroscopic hysteresis loops and polarization switching,which is the foundation of the practical usage of ultrathin ferroelectrics.

关键词： polarization ferroelectric maintained

Pyrochlore-based high-entropy ceramics for capacitive energy storage

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Journal of Advanced Ceramics 2022年第7期11卷 1179-1185页

作者： Yiying CHEN Junlei QI Minhao ZHANG Zixi LUO yuan-hua lin State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

High-performance dielectrics are widely used in high-power systems,electric vehicles,and aerospace,as key materials for capacitor *** application scenarios under these extreme conditions require ultra-high stability and reliability of the ***,a novel pyrochlore component with high-entropy design of Bi1.5Zn_(0.75)Mg_(0.25)Nb_(0.75)Ta_(0.75)O_(7)(BZMNT)bulk endows an excellent energy storage performance of Wrec≈2.72 J/cm3 together with an ultra-high energy efficiency of 91%at a significant enhanced electric field Eb of 650 kV/***,the temperature coefficient(TCC)of BZMNT(~−220 ppm/℃)is also found to be greatly improved compared with that of the pure Bi1.5ZnNb1.5O7(BZN)(~−300 ppm/℃),demonstrating its potential application in temperature-reliable *** high-entropy design results in lattice distortion that contributes to the polarization,while the retardation effect results in a reduction of grain size to submicron scale which enhances the *** high-entropy design provides a new strategy for improving the high energy storage performance of ceramic materials.

关键词： high entropy bismuth-based pyrochlore high-temperature stability energy storage

Colossal permittivity and ultralow dielectric loss in Nb-doped SrTiO_(3) ceramics

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Journal of Advanced Ceramics 2023年第12期12卷 2247-2256页

作者： Jinghan Cai Junlei Qi Yueyang Yang Xinyue Zhang yuan-hua lin State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

Defect engineering has been applied to prepare materials with modifiable dielectric ***3(x=0,0.003,0.006,0.009,0.012)ceramics were synthesized using the traditional solid-state reaction method and sintered in a reducing *** samples show excellent dielectric properties with giant permittivity(>3.5×10^(4))and low dielectric loss(<0.01).SrTiNb0.003O3 ceramic exhibits a colossal permittivity of 4.6×10^(4)and an ultralow dielectric loss of 0.005(1 kHz,room temperature)as well as great temperature stability in the range of(−60)–160℃.The mechanism of the presented colossal permittivity(CP)properties is investigated by conducting X-ray photoelectron spectroscopy(XPS)and analyzing activation *** results indicate that the introduction of Nb5+and the reducing sintering atmosphere together generated the formation of Ti^(3+)and V_(O)^(**).These defects further form Ti-V_(O)^(**)-Ti'_(Ti)defect dipoles,contributing to the coexisting giant permittivity and low dielectric loss in Nb-doped SrTiO_(3)(STN)ceramics.

关键词： SrTiO_(3) colossal permittivity(CP) ultralow dielectric loss defect dipoles

Thermoelectric thin films:Promising strategies and related mechanism on boosting energy conversion performance

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Journal of Materiomics 2020年第3期6卷 494-512页

作者： Xuxuan Chen Zhifang Zhou yuan-hua lin Cewen Nan State Key of Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing100084PR China

Thermoelectrics can be capable of direct and reversible conversion between heat and *** dimensional thermoelectric materials,especially two dimensional(2D)thin films,have been considered as a breakthrough to decouple the correlations between electronic and thermal transport,contributing to the optimization of thermoelectric *** the past few decades,some effective strategies combined with physical concepts like quantum confinement effect,energy filtering effect,band structure tuning and interface engineering are introduced to design high performance *** a thorough understanding the underlyingmechanisms is essential to develop thermoelectric ***,our review summarizes the major strategies that can be utilized in thermoelectric thin films,including fabrication of superlattice structure,formation of two-dimensional electron gas(2DEG)system,orientation regulation,strain engineering and magnetic manipulation,from the aspects of deep mechanisms analyses,recent progress and prospects,inspiring significant improvement of thermoelectric properties.

关键词： Thermoelectrics Thin film Strategy Mechanism

Self-etching Ni-Co hydroxides@Ni-Cu nanowire arrays with enhancing ultrahigh areal capacitance for flexible thin-film supercapacitors

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Rare Metals 2017年第9期36卷 691-697页

作者： Peng Guo Yang Shen Yu Song Jing Ma yuan-hua lin Ce-Wen Nan State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China Laboratory of Advanced Energy Storage Materials and Devices Research Institute of Tsinghua University in ShenzhenShenzhen 518057China

Flexible thin-film supercapacitors with high specific capacitance are highly desirable for modern wearable or micro-sized electrical and electronic applications. In this contribution, Ni-Co hydroxides（NCH）nanosheets were deposited on top of Ni-Cu alloy（NCA）nanowire arrays forming a freestanding thin-film composite electrode with hierarchical structure for *** electrochemical cycling, the dissolution of Cu into Cu ions will create more active sites on NCA, and the redeposited copper oxide can be coated onto NCH, giving rise to substantial increase in specific capacitance with cycling. Meanwhile, NCA and NCH have excellent conductivity, thus leading to excellent rate performance. This flexible thin-film electrode delivers an ultrahigh initial specific capacitance of 0.63 F·cm^（-2）（or 781.3 F·cm^（-3））.During charge-discharge cycles, the specific capacitance can increase up to 1.18 F·cm^（-2）（or 1475 F·cm^（-3）） along with the“self-etching”process. The electrode presents a better specific capacitance and rate capability compared with previously reported flexible thin-film electrode, and this novel design of etching technique may expand to other binary or ternary materials.

关键词： Nickel Cobalt Copper Hydroxides Supercapacitors

Nanonet-/fiber-structured flexible ceramic membrane enabling dielectric energy storage

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Journal of Advanced Ceramics 2023年第1期12卷 145-154页

作者： Lvye DOU Bingbing YANG Shun LAN Yiqian LIU yuan-hua lin Ce-Wen NAN State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

Ceramics are considered intrinsically brittle at macro scale due to the lack of slip mechanism and pre-existing defects,which greatly limits their potential applications in emerging fields including wearable electronic devices and flexible *** this contribution,we developed BiFeO_(3)/SiO_(2) dual-networks with exceptional flexibility through a coupled electronetting/electrospun *** hybrid nanostructured networks endow the material with high tensile strength(2.7 MPa),excellent flexibility(80%recoverable deformation),and robust fatigue resistance performance(maintain flexibility after a 1000-cyclic compress test).After in-situ compounded with dielectric polymer via a layer-by-layer solution casting method,the resultant three-dimensional(3D)composite film exhibits a twice higher dielectric constant(εr)than polyether imide(PEI)*** importantly,the breakdown strength of the 3D composite film is almost the same as that of the PEI film,resulting in an enhanced energy density of~6.0 J/cm^(3) and a high efficiency of 80%at 4.58 MV/*** unique structure,combined with the excellent balance between mechanical and dielectric properties in flexible structures,is of critical significance to the design of flexible functional ceramics and broadening their applications in wearable electric devices.

关键词： BiFeO_(3)/SiO_(2)dual-network flexible mechanically robust dielectric energy storage

Enhanced electrochemical performance of Si/C electrode through surface modification using SrF_(2) particle

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International Journal of Minerals,Metallurgy and Materials 2021年第10期28卷 1621-1628页

作者： Jun Yang yuan-hua lin Bing-shu Guo Ming-shan Wang Jun-chen Chen Zhi-yuan Ma Yun huang Xing Li School of New Energy and Materials Southwest Petroleum UniversityChengdu 610500China

The silicon-based material exhibits a high theoretical specific capacity and is one of the best anode for the next generation of advanced lithium-ion batteries(LIBs).However,it is difficult for the silicon-based anode to form a stable solid-state interphase(SEI)during Li alloy/de-alloy process due to the large volume change(up to 300%)between silicon and Li4.4Si,which seriously limits the cycle life of the ***,we use strontium fluoride(SrF_(2))particle to coat the silicon-carbon(Si/C)electrode(SrF_(2)@Si/C)to help forming a stable and high mechanical strength SEI by spontaneously embedding the SrF_(2) particle into *** the formed SEI can inhibit the volume expansion of the silicon-carbon anode during the *** electrochemical test results show that the cycle performance and the ionic conductivity of the SrF_(2)@Si/C anode has been significantly *** X-ray photoelectron spectroscopy(XPS)analysis reveals that there are fewer electrolyte decomposition products formed on the surface of the SrF_(2)@Si/C *** study provides a facile approach to overcome the problems of Si/C electrode during the electrochemical cycling,which will be beneficial to the industrial application of silicon-based anode materials.

关键词： silicon-based anode volume expansion strontium fluoride solid electrolyte interface cycling stability

Electrical and thermal transport behaviours of high-entropy perovskite thermoelectric oxides

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Journal of Advanced Ceramics 2021年第2期10卷 377-384页

作者： Yunpeng Zheng Mingchu Zou Wenyu Zhang Di Yi Jinle Lan Ce-Wen Nan yuan-hua lin State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing100084China State Key Laboratory of Organic-Inorganic Composites Beijing University of Chemical TechnologyBeijing100029China

Oxide-based ceramics could be promising thermoelectric materials because of their thermal and chemical stability at high ***,their mediocre electrical conductivity or high thermal conductivity is still a challenge for the use in commercial ***,we report significantly suppressed thermal conductivity in SrTiO_(3)-based thermoelectric ceramics via high-entropy strategy for the first time,and optimized electrical conductivity by defect *** high-entropy(Ca_(0.2)Sr_(0.2)Ba_(0.2)Pb_(0.2)La_(0.2))TiO_(3)bulks,the minimum thermal conductivity can be 1.17 W/(m·K)at 923 K,which should be ascribed to the large lattice distortion and the huge mass fluctuation *** power factor can reach about 295μW/(m·K^(2))by inducing oxygen ***,the ZT value of 0.2 can be realized at 873 K in this bulk *** approach proposed a new concept of high entropy into thermoelectric oxides,which could be generalized for designing high-performance thermoelectric oxides with low thermal conductivity.

关键词： high entropy thermoelectric oxides thermal conductivity electrical conductivity oxygen vacancy

Low-dimensional nanostructured photocatalysts

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Journal of Advanced Ceramics 2015年第3期4卷 159-182页

作者： Hao-Min XU huan-Chun WANG Yang SHEN yuan-hua lin Ce-Wen NAN State Key Laboratory of New Ceramics and Fine Processing School of Materials Science and EngineeringTsinghua UniversityBeijing 100084China

Low-dimensional nanostructures are a promising class of ideal high-performance candidates for energy storage and conversion owing to their unique structural,optical,and chemical ***-dimensional nanostructured photocatalysts have attracted ever-growing research *** this review,we mainly emphasize on summarizing the 0-,1-,and 2-dimensional nanostructured photocatalysts systematically,including their photocatalytic performance,synthesis methods,and theoretical *** the viewpoint of dimension,we try to figure out the way to design more high-efficiency photocatalysts towards numerous applications in the field of solar energy conversion,hoping to promote efficient control and rational development of photocatalysts.

关键词： low-dimension photocatalysis nanostructure