2000 Fiscal Year Final Research Report Summary
Chemical Analysis and Electronic Structure Studies of Vacancy-Type Defects by Measuring Positron Annihilation Momentum Distribution in Wide Range
| Project/Area Number |
10450229
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical properties of metals
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
HASEGAWA Masayuki TOHOKU UNIVERSITY, INSTITUTE FOR MATERIALS RESEARCH, PROFESSOR, 金属材料研究所, 教授 (80005975)
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| Co-Investigator(Kenkyū-buntansha) |
YUBUTA Kunio TOHOKU UNIVERSITY, INSTITUTE FOR MATERIALS RESEARCH, RESEARCH ASSOCIATE, 金属材料研究所, 助手 (00302208)
TANG Zheng TOHOKU UNIVERSITY, INSTITUTE FOR MATERIALS RESEARCH, RESEARCH ASSOCIATE, 金属材料研究所, 助手 (80271972)
NAGAI Yasuyoshi TOHOKU UNIVERSITY, INSTITUTE FOR MATERIALS RESEARCH, RESEARCH ASSOCIATE, 金属材料研究所, 助手 (10302209)
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| Project Period (FY) |
1998 – 2000
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| Keywords | Positron Annihilation / BCC-Cu / Nano-particles / Fermi Surface / Reactor Pressure Vessel Steels / Fe-Cu / Al-Cu-Mg / Magic Number Vacancy Clusters |
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| Research Abstract |
We have measured electron momentum distributions in wider ranges sampled by positrons in several metals and semiconductors using positron annihilation techniques of two dimensional angular correlation of annihilation radiation (2D-ACAR) and coincidence Doppler broadening (CDB). Marked results are as follows.
1) Fe-Cu model alloys for nuclear reactor pressure vessel (RPV) steels containing harmful Cu impurities.
A quantum-dot-like positron state is demonstrated in the defect-free Cu ultrafine particles embedded in Fe matrix. The wave functions of all positrons are entirely confined in the particles. The positrons in this state convey us usefu and exclusive information about the atomic and electronic structures of the particles. By 2D-ACAR experiments on Fe-1.0%Cu single crystals, we have determined the Fermi surface of BCC Cu ultrafine particles in Fe. The Fermi surface is almost spherical but has 12 necks around the centers of (110) Brillouin faces of the BCC structure.
In neutron-irradiated Fe-Cu model alloys, we have observed irradiation-induced microvoids of which inner surfaces are almost coated with Cu atoms. After annealing around 4O0℃, the dissociation of vacancies from the microvoids leads to the formation of Cu ultrafine particles.
2) Role of vacancy-solute complex in the initial rapid age hardening in Al-Cu-Mg alloy.
Using CDB method, we have found that quenched-in vacancies are bound to Mg atoms rather than Cu atoms initially and the vacancy-Mg complexes easily migrate to vacancy sinks at 150℃. Vacancy-Mg-Cu complexes form during the initial 1 min aging at vacancy sinks. The dislocation-solute interaction is the origin of the initial rapid hardening.
3) Mgic number vacanvy clusters in graphite and Si.
By combining positron annihilation experiments and first-principles calculation, we firstly observed magic number vacancies in a covalent-bond materials : graphite after neutron irradiation.
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Research Products
(14 results)
