| 研究実績の概要 |
Endohedral lithium-ion encapsulated fullerene (Li+@C60) is a commercially available emerging endohedral fullerene, whose electronic properties, structures and potential applications have been recently attracting considerable interest. Following this, neutral Li@C60 has been the next intriguing target because the existence of neutral lithium metal atom inside the fullerene cage represents the creation of a “super hydrogen atom”. However, the reported preparation of neutral Li@C60 is inefficient and time consuming. We have now achieved a facile, reliable, and efficient synthesis of neutral Li@C60 by chemical reaction using an easily available reducing agent, decamethylferrocene. With solid samples produced with this method in hand, we performed X-ray, Raman, and EPR studies. We found that Li@C60 obtained by chemical reduction contains a high proportion of radical monomer species (Li+@C60(-)) due to smaller formation yield of EPR silent dimerized (Li@C60)2. We believe that not only the new synthetic procedure for production but also the properties investigation undertaken contribute greatly to the understanding of this unique family of endohedral metallofullerenes, incorporating both Li+@C60 and Li@C60. As such the results achieved in this research will be of urgent nature and broad interest to the scientific community as they are of direct relevance to materials chemists and scientists, researchers working on functional molecular materials and to the extended pi-electron based molecular carbon community.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
Superconductors have no electrical resistance and carry electricity without losing energy. The development of new materials in order to achieve transition temperatures to zero-resistance as high as possible is at the extreme forefront of current challenges in materials science. C60 superconductors played leading role in materials research in the last 30 years achieving a robust zero-resistance state at record temperatures and surviving at extremely high magnetic fields. But they have reached their upper limit. Here we are facing the challenge of surpassing the past performance of C60 superconductors. We are targetting to achieve this by developing the uncharted field of high-symmetry superatomic carbon frameworks with metal ions inside the cages and using unprecedented mechanisms of electronic control by dual-direction internal and external electron doping. This is a challenging proposal because there are simply no systems of this type created before and, if and when made, theory predicts superb performance. Currently we have achieved the first milestone of producing and characterizing in the bulk the parent neutral lithium endohedral C60 fullerene - this constitutes the starting material, the synthon of our eventual targets and confirms that we are progressing at an excellent pace for this research.
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| 今後の研究の推進方策 |
Our research plan follows two complementary procedures: (i) to develop the new synthetic chemistry needed, and (ii) to combine it with advanced structural and physical property measurements and feedback from theory. The research will include: [1] Synthesis of dual-direction-doped A+n[Li+@C60(n+1)-] phases (A = alkali metal; n = 1-6). This will define the full range of valences and electronic ground states in C60 cages dually-electron-doped internally and externally. [2] Physical control of structure and properties. Application of pressure will be used to drive insulator-to-metal transitions and trigger the emergence of superconductivity out of non-superconducting A+n[Li+@C60(n+1)-] precursors away from half filling of the conduction band. [3] Electronic and magnetic ground states in the new materials. The strong interplay between crystal and electronic structure requires the use of many advanced experimental techniques at both ambient and elevated pressures. We have the expertise to employ the full range of experimental techniques to investigate crystal structure (synchrotron X-ray & neutron diffraction), electronic structure (magnetometry, transport properties, specific heat) and dynamics (NMR/muSR/EPR & IR/Raman spectroscopy) throughout the project duration. The integrated study of structure and electronic properties in the normal and superconducting states will be the basis for theoretical understanding of the new metallic/superconducting ground states.
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| 次年度使用額が生じた理由 |
The research started after the beginning of the financial year 2018 and at the beginning utilized pre-existing resources in the applicant's laboratory. Moreover, the emphasis of the project was initially (as described originally in the proposal) to isolate and purify (Li@C60)2. This was achieved by optimizing the bulk synthesis and purification of the neutral (Li@C60)2 dimer from the monomeric ionic precursor, (Li@C60)(PF6) targeting the availability of the material in large-quantities to allow full exploratory synthesis. This part of the work was successful and was achieved with resources well within our budget. The next steps involve more elaborate physical characterization as a function of temperature as well as the utilization of high pressure to enhance the properties. This will require significant resources including those carried over.
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