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自从1911年著名物理学家Onnes发现超导电性以来,人们不断努力提高超导转变温度,室温超导体是人类追逐的百年梦想。在近百年的研究历程中,铜基超导体、铁基超导体及麦克米兰极限MgB2超导体的发现不断刷新了人们对超导领域的认知,也增强了人们进一步提高超导转变温度和挖掘高温超导机制的信心。最近,理论预测并被实验验证的新型富氢化合物显示了高温乃至室温超导电性的巨大潜力,成为室温超导体的最佳候选体系之一。值得注意的是,高压下硫氢化物和镧氢化物均具有超过200 K的超导转变温度,引领了富氢化合物的研究热潮,涌现了一些重要的理论和实验成果。本文聚焦于目前富氢化合物超导体的实验研究进展,从不同氢结构单元及氢成键特征的角度总结和归纳新型富氢化合物的晶体结构性质及超导性能。主要介绍了5种在实验上成功获得的富氢化合物超导体:间隙型、离子型、共价型、笼型及分子型。通过对比分析不同类型的富氢化合物超导体,总结出一些影响超导转变温度的普适规律,并提出目前实验上亟待解决的问题和未来主攻的实验方向。 相似文献
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Pressure allows the precise tuning of a fundamental parameter, the interatomic distance, which controls the electronic structure and virtually all interatomic interactions that determine material properties. Hence, pressure tuning is an effective tool in the search for new materials with enhanced properties. To realize pressure tuning on matter, large-volume press(LVP) apparatuses have been widely used not only to synthesize novel materials but also to implement the in situ measurement of physical properties. Herein, we introduce the LVP apparatuses, including belt-type, cubic anvil, and 6–8 type multi-anvil, that will be constructed at the Synergetic Extreme Condition User Facility(SECUF) at Jilin University.Typically, cell volumes of 1000 mm~3 can be obtained at 20 GPa in a belt-type apparatus that is significantly larger than that obtained in a 6–8 type multi-anvil apparatus at the same pressure. Furthermore, the in situ measurement of physical properties, including thermological, electrical, and mechanical behaviors, is coupled to these LVP apparatuses. Some typical results of both synthetic experiments and in situ measurements obtained from the LVP apparatuses are also reviewed. 相似文献
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A systematical study of the orientational behavior of C60 molecules in single wall carbon nanotubes (SWCNTs) with different chirality and diameter has been performed by using a model of an infinite long nanotube filled with two C60 (denoted as C60-1 and C60-2) molecules. We studied the preferred orientation of the C60-1 molecule when the neighboring C60-2 molecule was fixed at the pentagon, double-bond, and hexagon orientations respectively. Our results showed that the C60-1 molecule prefers the pentagon (hexagon) orientation when the tube diameter is smaller (larger) than 1.31nm (1.36nm). For the tube diameter in between, the preferred molecular orientation of C60-1 changes from pentagon to hexagon with the increasing tube diameter when the neighboring C60-2 molecule is fixed at the pentagon or double-bond orientation. A novel vertex orientation for the C60-1 molecule has been found when the C60-2 molecule is fixed at the hexagon orientation. 相似文献
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In situ high pressure XRD diffraction and Raman spectroscopy have been performed on 12 nm CeO2 nanoparticles. Surprisingly, under quasihydrostatic conditions, 12 nm CeO2 nanoparticles maintain the fluorite-type structure in the whole pressure range (0-51 GPa) during the experiments, much more stable than the bulk counterpart (PT~31 GPa). In contrast, they experienced phase transition at pressure as low as 26 GPa under non-hydrostatic conditions (adopting CsCl as pressure medium). Additionally, 32-36 nm CeO2 nanoparticles exhibit an onset pressure of phase transition at 35 GPa under quasihydrostatic conditions, and this onset pressure is much lower than our result. Further analysis shows both the experimental condition (i.e., quasihydrostatic or non-hydrostatic) and grain size effect have a significant impact on the high pressure behaviors of CeO2 nanomaterials. 相似文献
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利用化学沉积法和溶胶法制备了粒径在20~100nm范围内不同的表面增强纳米结构活性银膜,系统地研究了单壁碳纳米管(SWCNT)的表面增强拉曼光谱(SERS)的G—band和D—band、比较玻璃和石英两种不同基片上的结果发现,单壁碳管的SERS谱随银膜粒径的变化有相同的变化趋势,G-band峰移对20~100nm范围内活性银膜粒径的差异不敏感,表明该波段所对应的碳管六元环本征振动比较稳定,与界面的化学相互作用较弱.D—band的峰形随基片和活性银膜粒径不同均有改变,且随着粒径变小,高频振动贡献有增大的趋势,表明无序碳与活性银膜间存在很强的相互作用。 相似文献
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本文采用基于从头算演化理论的晶体结构预测方法,对过渡金属锇(Os)的高压结构进行了系统研究. 结果表明,在0~1000 GPa压力范围内,金属Os一直保持六角密堆结构(hcp),没有发生结构相变,排除了前人提出的hcp到ω相变的可能. 我们深入利用赝势平面波方法和全电子缀加波方法对ω相(P6/mmm)及hcp相进行了优化,并比较了能量随体积(压强)的变化关系,两种方法均证实了我们的结论. 相似文献
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采用零温条件下的赝势-平面波方法和有限温度下的Car-Parrinello分子动力学方法,模拟了不同压力环境下氦原子在金属铌中的行为特征,研究了宿主缺陷和氦泡的形成机制。结果表明,闭电子壳层的氦原子在金属铌中具有刚球模型特征,其占据区域为金属自由电子的禁区,从而破坏铌原子之间的金属性键合。在常温条件下,局域高浓度的氦原子优先凝聚于近邻宿主空位缺陷处,从而形成氦泡;完整晶格中高浓度的氦将促使铌原子易位,形成间隙-空位模式的宿主缺陷,氦原子聚集于空位区域。完整宿主在压力(40 GPa)的作用下,晶格参数减小,铌原子之间的相互作用增强,尽管氦原子的存在削弱了铌原子之间的相互作用,位于格点上的铌原子仍难以借助热振动偏离格点形成空位,因而未能形成间隙-空位对和氦泡。 相似文献
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