2022 Fiscal Year Research-status Report
Accurate site-selective atomic structure determination by single-energy x-ray holography
| Project/Area Number |
20K15027
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| Research Institution | Nagoya University |
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Principal Investigator |
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| Project Period (FY) |
2020-04-01 – 2024-03-31
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| Keywords | x-ray holography / local structure / site-selectivity |
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| Outline of Annual Research Achievements |
The concept of site-selectivity is of great importance for modern materials science. It entails a full understanding of the atomic scale structure of the functional site in a material, which in turn largely determines its functional properties. New advances in x-ray fluorescence holography (XFH) have the potential to become a universal tool for site-selective investigations in crystals. These methods combine the intrinsic element-selectivity of XFH with the possibility for a chemical characterization of the environment. This is achieved by a resonant approach, i.e. tuning the x-ray energy to an energy that coincides with an x-ray absorption edge in the material. However, the approach is practically limited in the choice of energies, and the reconstruction from single-energy holographic data is still problematic. The proposed project aims to resolve these problems, to practically implement site-selective measurements and to apply them to current research issues in materials science. This approach is useful for, among else, identifying local atomic environments with chemical information and for understanding in detail the chemical disorder. One of the obstacles here is the atomic image cancellation effect, which leads to a large decrease in the signal intensity of certain pairs of distances and incident energies.
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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
The project is progressing smoothly. In this fiscal year, we investigated a Ni-Fe alloy using resonant x-ray fluorescence holography. These alloys have excellent properties and are widely used for scientific and practical purposes. Ni3Fe, which has a single-phase, fcc structure, is paramagnetic and disordered between 871 and 1715 K. It transforms to a ferromagnetic state at 871 K and to an ordered fcc structure at 773 K. Short-range order sets in as T approaches 773 K. The short-range order state can be obtained at room temperature by quenching the sample, and can be determined by Complex X-ray Fluorescence Holography. The results will strongly contribute to the further developments in the field of magnetic material. The data of the Ni-Fe alloy are now being analyzed.
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| Strategy for Future Research Activity |
After establishing the procedure for the Ni-Fe alloys, the next target will be more complex structures. These comprise in particular High Entropy Alloys, in which many different elements may occupy the same topological site. A detailed survey of the chemical fluctuations in these systems will expedite the understanding of these technologically important materials. Further targets are aperiodic systems (quasicrystals), for which the local structure is highly complex and short-range order information is highly sought after.
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| Causes of Carryover |
The budget set aside previously could not be fully utilized due to a delay with the experiments at large research facilities. It will be used for this purpose within the new fiscal year.
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