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Journal Articles

FE-SEM observations of multiple nanohillocks on SrTiO$$_{3}$$ irradiated with swift heavy ions

Kitamura, Akane; Ishikawa, Norito; Kondo, Keietsu; Fujimura, Yuki; Yamamoto, Shunya*; Yamaki, Tetsuya*

Transactions of the Materials Research Society of Japan, 44(3), p.85 - 88, 2019/06

Swift heavy ions can create nanosized hillocks on the surfaces of various ceramics. When these materials are irradiated with swift heavy ions at normal incidence, each ion impact results in the formation of a single hillock on the surfaces. In contrast, irradiation at grazing incidence forms chains of multiple hillocks on the surface, for example, for strontium titanate (SrTiO$$_{3}$$). So far, chains of multiple hillocks have been investigated using atomic force microscopy (AFM). It should be noted that AFM measurements involve systematic errors of several nanometers due to the finite size of the probe tip. Consequently, it is possible that the image of one hillock may merge with that of a neighboring hillock even if the two hillocks are well separated. In contrast to AFM, field-emission scanning electron microscopy (FE-SEM) is a useful technique for obtaining higher-resolution images. In this study, we observed multiple nanohillocks on the surfaces of SrTiO$$_{3}$$ using FE-SEM. Crystals of SrTiO$$_{3}$$(100) and 0.05 wt% Nb-doped SrTiO$$_{3}$$(100) were irradiated with 350 MeV Xe ions, respectively, at grazing incidence, where the angle between the sample surface and the beam was less than 2$$^{circ}$$. On the SrTiO$$_{3}$$ surface, a chain of periodic nanohillocks is created along the ion path. In contrast, black lines accompanied by hillocks are observed on the Nb-doped SrTiO$$_{3}$$ surface.

Journal Articles

Observation of simulated fuel debris using synchrotron radiation

Yoneda, Yasuhiro; Harada, Makoto; Takano, Masahide

Transactions of the Materials Research Society of Japan, 44(2), p.61 - 64, 2019/04

We performed three-dimensional observation of simulated fuel debris using Synchrotron Computed Tomography (CT). CT was used to make the inside of fuel debris clear. The CT observation provides that a clear contrast in the zirconia rich part and concrete rich part. Zirconia heavier than concrete moved to the lower part when crystals precipitate and aggregates near the bottom surface. As a result, phase separation occurs. The phase separation is caused by the difference in the composition ratio of zirconia, and can also be observed difference in crystal growth mode by composition ratio.

Oral presentation

TEM study of surface nanostructure of ceramics irradiated with swift heavy ions

Ishikawa, Norito; Taguchi, Tomitsugu*; Kitamura, Akane

no journal, , 

In most of the previous studies, hillocks have been imaged by atomic force microscopy (AFM). Although AFM is suitable for measuring height of hillocks, it is not suitable for measuring their diameter. Since diameter measurement by AFM is significantly affected by the curvature of the probe tip, most diameter data are subjected to a systematic error of some nanometers. One of the alternative methods for observing hillocks is to use transmission electron microscopy (TEM). Comparison between hillock diameter and ion track diameter is important for elucidating the mechanism of nanostructuring by SHI. In the present study, Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$ (yttrium iron garnet, YIG) were irradiated with various SHI having high electronic stopping power (20-35 keV/nm), and the as-irradiated samples were observed by TEM. As a result, the hillock diameter appears to be almost the same as the ion track diameter.

Oral presentation

Local structure of BaSn$$_{0.5}$$In$$_{0.5}$$O$$_{2.75}$$ as electrolyte for solid oxide fuel cell analyzed by EXAFS and neutron powder diffraction

Igawa, Naoki; Kodama, Katsuaki; Taguchi, Tomitsugu*; Tsuji, Takuya; Matsumura, Daiju; Yoshii, Kenji

no journal, , 

The local structure of BaSn$$_{0.5}$$In$$_{0.5}$$O$$_{2.75}$$ which is one of the excellent solid electrolytes for solid oxide fuel cells was analyzed by using the X-ray absorption spectroscopy followed the neutron diffraction. The average crystal structure analyzed by the neutron diffraction shows that BaSn$$_{0.5}$$In$$_{0.5}$$O$$_{0.5}$$ has the space group, ${it Pm}$-3${it m}$ and the Sn and In randomly occupy at same site. However, the result of Extended X-ray Absorption Fine Structure shows that the distance of In-O and Sn-O is different. In addition, the In-O distance is increased by the hydrogen doping while the Sn-O distance does not change. Those results suggest that the Sn and In occupy different sites and therefore the local structural distortion has occurred. In this work, the details of the local structure of BaSn$$_{0.5}$$In$$_{0.5}$$O$$_{2.75}$$ will be discussed.

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