2017 Fiscal Year Research-status Report
MXenes: A new family of two-dimensional materials for electronic and energy harvesting applications
| Project/Area Number |
17K14804
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| Research Institution | Institute of Physical and Chemical Research |
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Principal Investigator |
KHAZAEI Mohammad 国立研究開発法人理化学研究所, 計算科学研究機構, 研究員 (50431599)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | Chemical exfoliation / MAX Phases / MXenes / two-dimensional |
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| Outline of Annual Research Achievements |
There is a very important question that which of MAX phase compounds are promising candidates for exfoliation into two-dimensional transition metal carbides or nitride (so-called MXenes). In last fiscal, I performed extensive electronic structure and phonon calculations, and determined the force constants, bond strengths, and static exfoliation energies of MAX phases to MXenes for around 82 different experimentally synthesized MAX phases. I could show a clear correlation between the force constants and the bond strengths. As the total force constant of an “A” atom contributed from the neighboring atoms is smaller, the exfoliation energy becomes smaller, thus making exfoliation easier. I could propose 37 MAX phases for successful exfoliation into 2D MXenes. In addition, I explored the effect of charge injection on MAX phases. I found that the injected charges, both electrons and holes, are mainly received by the transition metals. This is due to the electronic property of MAX phases that the states near the Fermi energy are mainly dominated by d orbitals of the transition metals. For negatively charged MAX phases, the electrons injected cause swelling of the structure and elongation of the bond distances along the c axis, which hence weakens the binding. For positively charged MAX phases, on the other hand, the bonds become shorter and stronger. Therefore, we predict that the electron injection can significantly facilitate the exfoliation possibility of MAX phases to 2D MXenes. Our results have been published in the [Phys. Chem. Chem. Phys. 20, 8579 (2018)].
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In last fiscal year, in order to provide an insight into exfoliation possibilities of MAX phases into 2D MXenes, I had a very close collaboration with excellent theoretical physicists (Prof. Seiji Yunoki from RIKEN, Japan, and Prof. Keivan Esfarjani from University of Virginia, USA) and quantum chemist (Prof. Richard Dronskowski from Aachen University, Germany). Together, we could develop a good strategy to address our research question well. Fortunately, I had access to a very good computational facility. Therefore, I could perform the necessary calculations properly in shortest time. We analyzed our data quickly and summarized our results in a research paper, which has already been published. Hence, I think my research progress was rather smooth.
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| Strategy for Future Research Activity |
Recently, a group of MAX phases with in-plane ordered double transition metals, named as iMAX phases, have been synthesized. Experimentally, some of these iMAX phases have been chemically exfoliated into MXenes. Hence, we are investigating the structural stabilities and electronic structures of the experimentally discovered iMAX phases and their possible derivatives of MXenes. Our preliminarily results indicate that upon oxygen termination, some of the MXenes turn into semiconductors. Due to the absence of centrosymmetry in these systems, the semiconducting MXenes may have applications in piezoelectricity. Our calculations reveal that semiconducting MXenes possess giant piezoelectric coefficients as large as 45 pC/m. We are going to explore piezoelectric properties of MXenes in more detail.
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| Causes of Carryover |
In last fiscal year, I mainly focused on my research to proceed it and obtain good results. Hence, I could not use all my research budget. I just could find enough time to attended in two international conferences and I invited Prof. Amir Abbas Farajian from Wright State University, United States here to discuss about two-dimensional systems, particularly about MXenes. However, In this fiscal year, I am going to attend several international conferences and workshops and visit some of the experimental groups. Also, I have already invited several experimentalis and theoretical physicists in the field of MXenes from United States to visit us to start a new collaboration with them.
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