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論文

Preparation, thermoelectric properties, and crystal structure of boron-doped Mg$$_{2}$$Si single crystals

林 慶*; 齋藤 亘*; 杉本 和哉*; 大山 研司*; 林 好一*; 八方 直久*; 原田 正英; 及川 健一; 稲村 泰弘; 宮崎 譲*

AIP Advances (Internet), 10(3), p.035115_1 - 035115_7, 2020/03

 被引用回数:5 パーセンタイル:68.88(Nanoscience & Nanotechnology)

Mg$$_{2}$$Si is a potential thermoelectric (TE) material that can directly convert waste energy into electricity. In expectation of improving its TE performance by increasing electron carrier concentration, the element boron (B) is doped in Mg$$_{2}$$Si single crystals (SCs). Their detailed crystal structures are definitely determined by using white neutron holography and single-crystal X-ray diffraction (SC-XRD) measurements. The white neutron holography measurement proves that the doped B atom successfully substitutes for the Mg site. The SC-XRD measurement confirms the B-doping site and also reveals the presence of the defect of Si vacancy (VSi) in the B-doped Mg$$_{2}$$Si SCs. Regarding TE properties, the electrical conductivity, $$sigma$$, and the Seebeck coefficient, S, decreases and increases, respectively, due to the decrease in the electron carrier concentration, contrary to the expectation. The power factor of the B-doped Mg$$_{2}$$Si SCs evaluated from $$sigma$$ and S does not increase but rather decreases by the B-doping.

論文

Multiple-wavelength neutron holography with pulsed neutrons

林 好一*; 大山 研司*; 八方 直久*; 松下 智裕*; 細川 伸也*; 原田 正英; 稲村 泰弘; 仁谷 浩明*; 宍戸 統悦*; 湯葢 邦夫*

Science Advances (Internet), 3(8), p.e1700294_1 - e1700294_7, 2017/08

Local structures around impurities in solids provide important information for understanding the mechanisms of material functions, because most of them are controlled by dopants. For this purpose, the X-ray absorption fine structure method, which provides radial distribution functions around specific elements, is most widely used. However, a similar method using neutron techniques has not yet been developed. If one can establish a method of local structural analysis with neutrons, then a new frontier of materials science can be explored owing to the specific nature of neutron scattering-that is, its high sensitivity to light elements and magnetic moments. Multiple-wavelength neutron holography using the time-of-flight technique with pulsed neutrons has great potential to realize this. We demonstrated multiple-wavelength neutron holography using a Eu-doped CaF$$_{2}$$ single crystal and obtained a clear three-dimensional atomic image around trivalent Eu substituted for divalent Ca, revealing an interesting feature of the local structure that allows it to maintain charge neutrality. The new holography technique is expected to provide new information on local structures using the neutron technique.

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