ISAFM 2019-----------------------------------------------------------------------------------------------------------------------------------------------------P-type thermoelectric properties of stoichiometric full-Heusler alloy
Fe2TiSn sintered samples○Toshiki OZAKI and Hiroshi NAKATSUGAWA

Graduate School of Engineering Science, Materials Science, Yokohama National University79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501 JAPANozaki-toshiki-fh@ynu.jp
Abstract
Full Heusler alloy Fe2TiSn is predicted to show high S at 200℃ or lower from first principles
calculation by Yabuchi1). On the other hand, the thermal conductivity κ is about 7 times higher thanthat of the Bi – Te practically used as a thermoelectric material, so reducing κ is an important issue.
In this research, focusing on the advantage of powder metallurgy method which is easy to process
into target shape and can produce dense specimen with less segregation, we focused on the sinteredbody specimen from mechanically homogenized powder while adjusting the milling time wasprepared. In particular, it aims at controlling further grain refinement, promoting phonon scattering
at grain boundaries, reducing κ of Fe2TiSn sintered body, and further improving thermoelectriccharacteristics.
I. Experimental investigation
Samples were prepared by weighing Fe, Ti, Sn of 99.9% purity with a stoichiometric composition
ratio of 2: 1: 1 and using an arc melting furnace. Six types of powder were prepared in air and in an
Ar atmosphere at 1080 rpm using a stainless ball (φ 5 mm) while changing the milling time to 1, 3,
12 h. After press molding, the sintered body was calcined at 450℃ for 2 h under a vacuum of 4 Pa,vacuum sealed in a quartz tube, and subjected to homogenization annealing at 800℃ for 48 h. From
the XRD, crystal structure parameters were identified, composition analysis of ingots and sinteredbodies from EPMA, SEM observation of powders and sintered bodies, microstructural changes andcrystal grain size analysis of sintered bodies were carried out. Thermoelectric properties wereevaluated by the change of dimensionless figure of merit ZT by S · ρ measurement by ResiTest 8300
and κ measurement by PEM-2.

Reference

AirAr

ingot
1h milling3h milling–1

12h milling101

 / Wm K

II. Results and Conclusion
From the SEM observation, the grain size of thesintered body progressed by increasing milling time,
the average grain size was 0.86 μm in the sample of1h, and 0.69 μm in the sample of 12h, and dispersionof particle size also decreased. In addition, as shownin Fig.1, as compared with the sample cut out fromthe ingot, κ was clearly reduced in the sintered body,but no change in κ due to the atmosphere during
milling was observed. In particular, in the sinteredbody subjected to milling at 12h, 45% reduction in κ
is realized at around room temperature as comparedwith the ingot sample. In the lecture, as a result ofEPMA, we will also discuss the measurement resultsof S and ρ and the change of ZT.

0300

350
T/K400

Fig.1 Temperature dependence of thermal
conductivity κ.

1) S.Yabuuchi, M.Okamoto, A.Nishide, Y.Kurosaki, J.Hayakawa, Appl. Phys. Expr., 6, 025504 (2013).

----------------------------------------------------------------------------------------------------------------------------------------------------March 5-7, 201912Changwon, Korea