共查询到20条相似文献,搜索用时 78 毫秒
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用离散变分密度泛函分子轨道方法(DFT-DVM)和线性扩展平面波能带方法(LAPW)计算了Bi2Te3与SnBi2Te4,讨论了电子结构与热电性能之间的关系.Te(Ⅱ)-Bi离子键强度和Te(Ⅰ)-Bi差别不大,而Te(Ⅱ)-Bi共价键比Te(Ⅰ)-Bi强.Te(Ⅰ)-Te(Ⅰ)原子层之间的主要相互作用是范得华力而最弱.Bi2Te3掺Sn后Te-Bi离子键增强而共价键减弱,且费米能级处带隙变小.Sn主要影响导带结构. 相似文献
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研究了用低温湿化学法和水热法制备纳米级的Bi2Te3和sb挪e3颗粒,并通过透射电镜观察其微观形貌。Bi2Te3粉末的微观形貌为直径在30-50n之间的片状小颗粒,而sb2Te3颗粒的微观形貌为薄带状,直径约为70nm,长度则为从150-300nm不等,并对其晶体的形核和长大机理进行了讨论。认为,纳米小颗粒状的Bi2Te3晶体可能是通过“表面形核和侧向生长”形成的产物,而薄带状的sb2Te3晶体可能是在Te块解体形成的条带状碎屑基础上形成的。用放电等离子烧结法(spark plasma sintering)制备不同比例的Bi2Te3/Sb2Te3块状复合材料,测量并比较了其热电性能。通过改变Bi2Te3的量,可以提高复合材料的电性能。成分不同的层片间的散射,能更有效地降低块体材料的热导率。在500K的温度下,Bi2Te3和sb2Te3以摩尔比为1:1复合烧结的试样的热导率低达0.7W/(m·K)。进一步优化Bi2Te3和sb2Te3的复合比例,其热电性能可能会有进一步的提高。 相似文献
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热电材料的低维化可以改善材料电输运与热传输的矛盾,特别是一维纳米热电材料明显的晶体各向异性和强烈的量子禁闭效应,可大幅度提高材料的热电优值和热电转换效率。Bi2Te3是制造低温热电材料的最常用材料,在温差发电和半导体制冷方面具有广阔的商业应用前景。以一维Bi2Te3基纳米热电材料的制备技术为评述线索,重点论述一维Bi2Te3基纳米热电材料形貌参数(包括直径、长径比)、晶面取向等微观结构的调控方法、生长机理以及显微结构对热电性能的影响规律。指出发展新的一维Bi2Te3基纳米热电材料结构控制方法,研究一维纳米热电材料的定向排布及组装技术,从更深层次揭示一维结构与热电性能的关系,以及开发一维Bi2Te3基纳米热电材料在各领域的实际应用是未来研究的发展方向。 相似文献
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稀土元素对Bi2Te3基材料热电性能的影响一直是Bi2Te3基热电材料研究的热点。本文研究了不同Gd掺杂量Bi2Te3基热电材料的热压烧结工艺参数,运用XRD,SEM方法对材料的物相成分和形貌进行了表征,研究了20MPa下不同Gd掺杂对Bi2Te3基材料的载流子浓度、电导率、Seebeck系数的影响。研究结果表明,Gd掺杂没有明显改变Bi2Te3基材料的晶体结构,适量的Gd掺杂有利于减小载流子浓度、提高Bi2Te3基材料的热电性能。 相似文献
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Chiral materials are widely applied in various fields such as enantiomeric separation, asymmetric catalysis, and chiroptical effects, providing stereospecific conditions and environments. Supramolecular concepts to create the chiral materials can provide an insight for emerging chiro-optical properties due to their well-defined scaffolds and the precise functionalization of the surfaces or skeletons. Among the various supramolecular chiral structures, 2D chiral sheet structures are particularly interesting materials because of their extremely high surface area coupled with many unique chemical and physical properties, thereby offering potential for the next generation of functional materials for optically active systems and optoelectronic devices. Nevertheless, relatively limited examples for 2D chiral materials exhibiting specific functionality have been reported because incorporation of molecular chirality into 2D architectures is difficult at the present stage. Here, a brief overview of the recent advances is provided on the construction of chiral supramolecular 2D materials and their functions. The design principles toward 2D chirality and their potential applications are also discussed. 相似文献
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Multistimuli Response Micro‐ and Nanolayers of a Coordination Polymer Based on Cu2I2 Chains Linked by 2‐Aminopyrazine
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J. Conesa‐Egea J. Gallardo‐Martínez S. Delgado J. I. Martínez J. Gonzalez‐Platas V. Fernández‐Moreira U. R. Rodríguez‐Mendoza P. Ocón F. Zamora P. Amo‐Ochoa 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(33)
A nonporous laminar coordination polymer of formula [Cu2I2(2‐aminopyrazine)]n is prepared by direct reaction between CuI and 2‐aminopyrazine, two industrially available building blocks. The fine tuning of the reaction conditions allows obtaining [Cu2I2(2‐aminopyrazine)]n in micrometric and nanometric sizes with same structure and composition. Interestingly, both materials show similar reversible thermo‐ and pressure‐luminescent response as well as reversible electrical response to volatile organic solvents such as acetic acid. X‐ray diffraction studies under different conditions, temperatures and pressures, in combination with theoretical calculations allow rationalizing the physical properties of this compound and its changes under physical stimuli. Thus, the emission dramatically increases when lowering the temperature, while an enhancement of the pressure produces a decrease in the emission intensity. These observations emerge as a direct consequence of the high structural flexibility of the Cu2I2 chains which undergo a contraction in Cu? Cu distances as far as temperature decreases or pressure increases. However, the strong structural changes observed under high pressure lead to an unexpected effect that produces a less effective Cu? Cu orbital overlapping that justifies the decrease in the intensity emission. This work shows the high potential of materials based on Cu2I2 chains for new applications. 相似文献
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The dielectric properties of nanophase Ag2HgI4 and Ag2HgI4-Al2O3 nanocomposites at different frequencies have been studied over a temperature range covering the stability range of β phase
of Ag2HgI4 and beyond the β to a phase transition temperature. έ′, tan δ and σa.c. of nanophase Ag2HgI4 and Ag2HgI4-Al2O3 nanocomposites were found to be larger than the reported values for polycrystalline pellets of Ag2HgI4. The dielectric properties of the nanocomposites were found to be a function of the wt.% of nano alumina. The observed changes
are attributed to the grain boundary properties of nanophase materials and to the microsize space charge effects. 相似文献
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用固相反应法制备(Gd1-xErx)2(Zr0.8Ti0.2)2O7(摩尔分数x=0,0.2,0.4)陶瓷并测试其晶体结构、显微形貌和物理性能,研究了Er2O3掺杂的影响。结果表明,(Gd1-xErx)2(Zr0.8Ti0.2)2O7陶瓷具有立方烧绿石结构,显微结构致密,在室温至1200℃高温相的稳定性良好;Er3+掺杂降低了陶瓷材料的热导率和平均热膨胀系数,当x=0.2时,其1000℃的热导率最低(为1.26 W·m-1·k-1)。同时,Er3+掺杂还提高了这种材料的硬度和断裂韧性。 相似文献
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J. Arout Chelvane S. Kasiviswanathan M. V. Rao G. Markandeyulu 《Bulletin of Materials Science》2004,27(2):169-173
The magnetic properties of ball-milled TbFe2 and TbFe2B were studied by magnetization measurements. X-ray diffraction studies on TbFe2B showed that boron occupied interstitial position in the crystal structure, just as hydrogen did. The value of the saturation
magnetization of TbFe2B was found to be smaller than that of TbFe2. This is explained on the basis of a charge transfer between the boron atoms and the 3d band of Fe. The anisotropy of TbFe2B was found to be large compared to that of TbFe2. X-ray diffractograms for the ball milled samples showed that after 80 h of milling, a predominantly amorphous phase was
obtained. TbFe2B was found to undergo easy amorphization compared to TbFe2. Magnetization of TbFe2 was found to decrease rapidly with initial milling hours and was found to be constant with further hours of milling. TbFe2B exhibited an anomalous behaviour with an increase in moment with milling hours and this may be due to the segregation of
α-Fe. 相似文献
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Dipesh B. Trivedi Guven Turgut Ying Qin Mohammed Y. Sayyad Debarati Hajra Madeleine Howell Lei Liu Sijie Yang Naim Hossain Patoary Han Li Marko M. Petrić Moritz Meyer Malte Kremser Matteo Barbone Giancarlo Soavi Andreas V. Stier Kai Müller Shize Yang Ivan Sanchez Esqueda Houlong Zhuang Jonathan J. Finley Sefaattin Tongay 《Advanced materials (Deerfield Beach, Fla.)》2020,32(50):2006320
Janus crystals represent an exciting class of 2D materials with different atomic species on their upper and lower facets. Theories have predicted that this symmetry breaking induces an electric field and leads to a wealth of novel properties, such as large Rashba spin–orbit coupling and formation of strongly correlated electronic states. Monolayer MoSSe Janus crystals have been synthesized by two methods, via controlled sulfurization of monolayer MoSe2 and via plasma stripping followed thermal annealing of MoS2. However, the high processing temperatures prevent growth of other Janus materials and their heterostructures. Here, a room-temperature technique for the synthesis of a variety of Janus monolayers with high structural and optical quality is reported. This process involves low-energy reactive radical precursors, which enables selective removal and replacement of the uppermost chalcogen layer, thus transforming classical transition metal dichalcogenides into a Janus structure. The resulting materials show clear mixed character for their excitonic transitions, and more importantly, the presented room-temperature method enables the demonstration of first vertical and lateral heterojunctions of 2D Janus TMDs. The results present significant and pioneering advances in the synthesis of new classes of 2D materials, and pave the way for the creation of heterostructures from 2D Janus layers. 相似文献