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IntroductionThethirdmemberofthehomologousseriesofHg Ba2 Can - 1CunO2n + 2 (Hg 12 2 3)wasreportedtobeasuper conductoratthehighesttransitiontemperatureof 133K ,1whichmakesitthemostattractive.ThedirectinformationontheCuionsiteattheatomiclevelisimportantforelucidatingthesuperconductivitymechanism .Sotheneedforamicro scopicprobesuchasM ssbauerspectroscopyisself evident.AnumberofpapersonM ssbauerspectroscopyhavebeenre ported .2 Nevertheless ,therearestillcontroversiesconcerningthespectrumfitsan… 相似文献
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We investigate hexagonal BC2N in graphite unit cells using the first-principles method and calculate the total energies, lattice parameters, and electronic band structures after full relaxation. It is shown that stable hexagonal BC2N should be stacked sequentially with one graphite layer and one h-BN layer. The density of states indicates that this structure should have metallicity. 相似文献
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Both boron nitride(BN) and carbon(C) have sp, sp2 and sp3 hybridization modes, thus resulting in a variety of BN and C polymorphs with similar structures, such as hexagonal BN(h BN) and graphite, cubic BN(c BN)and diamond. Here, five types of BN polymorph structures are proposed theoretically, inspired by the graphitediamond hybrid structures discovered in a recent experiment. These BN polymorphs with graphite-diamond hybrid structures possess excellent mechanical propertie... 相似文献
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采用高压合成技术,在1.5 GPa,900 K的合成压力和温度条件下成功合成出了系列Fe置换掺杂型方钴矿化合物FexCo4-xSb12 ,其中x= 0,0.2,0.6,0.8. 详细研究了FexCo4-xSb12 样品在300 K ~ 700 K温度范围内的电阻率、Seebeck系数和功率因子(S2σ)随温度和Fe掺杂量的变化关系. 研究结果表明:在测试温度范围内,随着温度的升高,样品的电阻率和Seebeck系数逐渐增大. 随着Fe含量的增加,样品的电阻率和Seebeck系数先增加后减小. 与常压下相同样品比较,高压合成方法制备的样品的电学输运特性有了明显的提高. 上述研究结果表明,高压合成技术在制备热电材料方面能够有效地提高样品的电输运特性. 相似文献
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液固Gibbs自由能差是决定材料非晶转变的热力学关键因素,但该参量在预测非晶转变和指导非晶成分设计方面仍有一些基本问题有待解决.其中,一个关键问题是:作为Gibbs能差的两个核心要素,焓与熵,二者在决定和控制非晶转变中关系并不明确.基于课题组系列研究结果,本文就焓与熵在材料非晶转变中的协同性与独立性问题进行了全面探讨,发现二者在决定非晶形成上具有很强的相关性.理论分析和实验测量相结合,展示了材料熔化熵与熔点粘度、混合焓等多个非晶形成经典参量之间的内在关联,证实熔化熵与材料非晶形成之间的密切关联;并从多个角度证实材料低熔化熵有利于非晶形成,纠正了传统上基于经典形核理论得出的高熔化熵有利于非晶形成的认识.研究也发现,决定非晶形成的关键动力学与热力学参量,如粘度和混合焓,均可通过熔化熵得到表达.进而论证了熔化熵在评估非晶形成、指导非晶成分设计中的可靠性和有效性,由此提出熔化熵可作为理解指导材料非晶形成的代表性热力学参量.系列成果为发展非晶形成热力学、深入理解材料非晶形成提供了参考与思路. 相似文献
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Design of a Class of New sp2-sp3 Carbons Constructed by Graphite and Diamond Building Blocks
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The sp2–sp3-hybridized carbon allotropes with the advantage of two hybrid structures possess rich and fascinating electronic and mechanical properties and they have received long-standing attention.We design a class of versatile sp2–sp3carbons composed of graphite and diamond structural units with variable sizes.This class of sp2–sp3carbons is energetically more favorable than graphite under high pressure,and their mechanical and dynamical stabilities are further confirmed at ambient pressure.The calculations of band structure and mechanical properties indicate that this class of sp2–sp3carbons not only exhibits peculiar electronic characteristics adjusted from semiconducting to metallic nature but also presents excellent mechanical characteristics,such as superhigh hardness and high ductility.These sp2–sp3carbons have desirable properties across a broad range of potential applications. 相似文献
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EFFECTS OF THE QUALITY OF SUBSTRATE ON THE STRUCTURE AND SUPERCONDUCTING PROPERTIES OF Yba2Cu3O7-x THIN FILM
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We have systematically investigated the structures, morphologies, microwave surface resistance, DC performances and the substrate qualities of three YBa2Cu3O7-x(YBCO) thin films 30mm in diameter. The three samples deposited by the same process have been proved of different properties. It has been shown that the structure and superconducting properties of the thin film depend strongly on the quality of substrate. 相似文献
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采用φ50.8m (即2 in)YBCO*/YBCO/CeO2 /YSZ/Si多层膜制成的磁通变换器与SrTiO3 双晶上制备的尺寸为10mm×5mm平面式DC-SQUID梯度计构成一个倒装片梯度计 .磁通变换器与平面梯度计之间的耦合系数为0.18.磁通变换器有效地提高了梯度计的磁场梯度分辨率.倒装片式梯度计在白噪声区的磁场梯度分辨率为73fT·cm-1·Hz-1/ 2 ,在1Hz下 ,磁场梯度分辨率为596fT·cm-1·Hz-1/ 2 .在无屏蔽条件下 ,采用该梯度计成功地测得了高质量心磁图 . 相似文献
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EFFECTS OF THE QUALITY OF SUBSTRATE ON THE STRUCTURE AND SUPERCONDUCTING PROPERTIES OF Yba2Cu3O7-x THIN FILM
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We have systematically investigated the structures, morphologies, microwave surface resistance, DC performances and the substrate qualities of three YBa2Cu3O7-x(YBCO) thin films 30mm in diameter. The three samples deposited by the same process have been proved of different properties. It has been shown that the structure and superconducting properties of the thin film depend strongly on the quality of substrate. 相似文献