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Effect of Vacancy-Site Occupation in Half-Heusler Compound ZrNiSn on Phase Stability and Thermoelectric Properties

Published online by Cambridge University Press:  07 March 2011

Yoshisato Kimura
Affiliation:
Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Department of Materials Science and Engineering, 4259-G3-23 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.
Toshiyasu Tanoguchi
Affiliation:
Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Department of Materials Science and Engineering, 4259-G3-23 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.
Yasuhiro Sakai
Affiliation:
Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Department of Materials Science and Engineering, 4259-G3-23 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.
Yaw-Wang Chai
Affiliation:
Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Department of Materials Science and Engineering, 4259-G3-23 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.
Yoshinao Mishima
Affiliation:
Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Department of Materials Science and Engineering, 4259-G3-23 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.
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Abstract

The half-Heusler compound ZrNiSn has a quite small solubility for Ni from the stoichiometric composition towards the Ni-rich direction since Ni atoms are not supposed to occupy the vacancy-site. Nevertheless, Co and Ir atoms preferably occupy the vacancy-site of ZrNiSn, which is contrary to the prediction that they would substitute for Ni sites. This implies that the phase stability of the compound gradually changes toward that of the Heusler compound Zr(Ni,M)2Sn (M = Co, Ir). It has been confirmed that there exists a two-phase field between half-Heusler Zr(Ni,Cox)Sn and Heusler Zr(Ni,Co)2Sn. The n-type thermoelectric property of ZrNiSn can be converted to p-type by the addition of Co and Ir within the compositional range of the half-Heusler phase. The occupation of vacancy sites by Co and Ir atoms leads to a drastic reduction in the thermal conductivity owing to the enhancement of phonon scattering. With further Co addition, the Heusler phase Zr(Ni,Co)2Sn alloys show metallic behavior.

Type
Research Article
Copyright
Copyright © Materials Research Society 2011

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