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Stability of amorphous Ta–O nanotubes prepared by anodization: Thermal and structural analyses

Published online by Cambridge University Press:  31 March 2014

Ryusuke Nakamura*
Affiliation:
Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Naka-ku, Sakai 599-8531, Japan
Kohta Asano
Affiliation:
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8565, Japan
Manabu Ishimaru
Affiliation:
Department of Materials Science and Engineering, Kyushu Institute of Technology, Tobata, Kitakyushu, Fukuoka 804-8550, Japan
Kazuhisa Sato
Affiliation:
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Masahide Takahashi
Affiliation:
Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
Hiroshi Numakura
Affiliation:
Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan
*
a)Address all correspondence to this author. e-mail: nakamura@mtr.osakafu-u.ac.jp
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Abstract

Amorphous Ta–O nanotubes (NTs) prepared by anodization in a sulfuric-acid-based solution have been found to contain considerable amounts of extra oxygen and sulfur. Their structural and thermal stability has been studied by combining x-ray diffractometry, transmission electron microscopy, and thermal analysis. The amorphous Ta–O, whose composition was estimated to be Ta2O6.6S0.7, crystallizes into orthorhombic β-Ta2O5 at temperatures around 1073 K by an endothermic reaction, at which excess oxygen and impurity sulfur are released. The amorphous NTs were found to be thermally more stable than stoichiometric amorphous Ta2O5, whose crystallization temperature is around 973 K. Excess oxygen and impurity sulfur, which form chemical bonds with Ta atoms in the amorphous solid, must be the origin of the stability. The crystallization follows the out-diffusion of oxygen and sulfur from the solid at temperatures where the mobility of atoms is high enough, indicating that the crystallization is kinetically arrested.

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Articles
Copyright
Copyright © Materials Research Society 2014 

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References

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