Significant off-stoichiometry effect leading to the N-type conduction and ferromagnetic properties in titanium doped Fe2VAl thin films
Significant off-stoichiometry effect leading to the N-type conduction and ferromagnetic properties in titanium doped Fe2VAl thin films
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DOI：
10.1016/j.actamat.2020.09.067
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发表时间：
2020-11-01
期刊：
影响因子：
9.4
通讯作者：
Mori, Takao
中科院分区：
文献类型：
--
作者：
Gao, Weihong;Liu, Zihang;Mori, Takao
热电薄膜对于通过能量收集为物联网（IoT）节点提供自供电具有重要意义。heusler型Fe2VAl在室温热电应用方面引起了人们的关注。然而，总体热导率大导致性能差，限制了目前的研究。本文报道了用磁控溅射法在石英衬底上生长Fe2V0.9Ti0.1Al薄膜的结构、热电和磁性能的综合研究。研究发现，高温退火比低温长时间退火更能稳定Fe2VAl的L2(1)型结构，使其Seebeck系数大得多，导热系数略高。更重要的是，显著的非化学计量现象，即富铁成分，有助于薄膜的n型导电。采用皮秒和纳秒时域热反射技术成功测量了薄膜的热导率，仅为块体材料的三分之一，证明了利用纳米结构降低Fe2VAl热导率的有效性。此外，磁化率测量表明薄膜是铁磁体，而块体样品具有顺磁性。我们的发现为Fe2VAl薄膜的组成-结构-性能关系提供了新的思路，为未来的相关应用提供了新的思路。(C) 2020材料学报Elsevier Ltd.出版。版权所有。
Thermoelectric thin films are of great interest for self-powering Internet of Things (IoT) nodes via energy harvesting. Heusler-type Fe2VAl attracts some attention for room-temperature thermoelectric applications. However, the large overall thermal conductivity leads to a poor performance that restricts the current investigations. Herein, we report a comprehensive study of structural, thermoelectric, and magnetic properties of Fe2V0.9Ti0.1Al thin films on quartz substrate, grown by magnetron sputtering. It is found that high-temperature annealing is more effective than the long-time annealing at the low temperatures to stabilize the L2(1) type structure of Fe2VAl, leading to a much larger Seebeck coefficient and slightly higher thermal conductivity. More importantly, the significant off-stoichiometry phenomenon, namely Fe-rich composition, contributes to n-type conduction of thin films. Both the picosecond and nanosecond time-domain thermoreflectance techniques were employed to successfully measure the thin-film thermal conductivities, merely one-third of bulk material, demonstrating the effectiveness of utilizing nanostructuring to reduce the thermal conductivity of Fe2VAl Moreover, magnetic susceptibility measurements reveal that thin films are ferromagnets, while the bulk sample is characterized by paramagnetism. Our finding sheds new light on the composition-structure-property relationship of Fe2VAl thin films for future related applications. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.