Phase stability and thermoelectric properties of semiconductor-like tetragonal FeAl2
Phase stability and thermoelectric properties of semiconductor-like tetragonal FeAl2
复制标题
类半导体四方FeAl2的相稳定性和热电性能
DOI：
10.1080/14686996.2019.1662272
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发表时间：
2019
影响因子：
5.5
通讯作者：
Kimura Kaoru
中科院分区：
文献类型：
--
作者：
Tobita Kazuki;Kitahara Koichi;Katsura Yukari;Sato Naoki;Nishio-Hamane Daisuke;Gotou Hirotada;Kimura Kaoru
四元FeAl 2是一个高压相，并预测表现出类似超导体的行为。利用同步辐射原位X射线衍射技术，在20 GPa压力下加热样品，研究了四元FeAl_2的压力和温度合成条件。在确定的最佳工艺条件下，采用多砧压机在7.5GPa和873 K下合成了四元FeAl_2多晶样品，并测量了其热电性能。四元系FeAl 2的Seebeck系数在155 K时为-105 μV/K的负值，在400 K时迅速变为75 μV/K的正值。虽然这些值是Fe-Al合金中最大的，但最大功率因数仍保持在0.41 mW/mK 2，因为载流子浓度未被调谐。通过对四元FeAl_2、三斜FeAl_2和FeAl+ Fe_2Al_5的吉布斯自由能的比较，发现四元FeAl_2由于其振动熵贡献较小，随着温度的升高而变得不稳定。
Tetragonal FeAl2is a high-pressure phase and is predicted to exhibit semiconductor-like behavior. We investigated the pressure and temperature synthesizing conditions of tetragonal FeAl2, supported byin situX-ray diffractions, using synchrotron radiation during heating the sample under a pressure of 20 GPa. Based on the determined optimal conditions, we synthesized the bulk polycrystalline samples of tetragonal FeAl2at 7.5 GPa and 873 K, using a multi-anvil press and measured its thermoelectric properties. The Seebeck coefficient of tetragonal FeAl2showed a large negative value of – 105 μV/K at 155 K and rapidly changed to a positive value of 75 μV/K at 400 K. Although these values are the largest among those of Fe–Al alloys, the maximum power factor remained at 0.41 mW/mK2because the carrier concentration was not tuned. A comparison of the Gibbs free energy of tetragonal FeAl2, triclinic FeAl2and FeAl+Fe2Al5revealed that tetragonal FeAl2became unstable as the temperature increased, because of its smaller contribution of vibrational entropy.