正负磁阻共存的Fe/Bi0.5Sb1.5Te3热电磁薄膜

柯少秋; 叶先峰; 张昊俊; 聂晓蕾; 陈天天; 刘承姗; 朱婉婷; 魏平; 赵文俞

doi:10.7498/aps.73.20240701

正负磁阻共存的Fe/Bi_0.5Sb_1.5Te₃热电磁薄膜

武汉理工大学, 材料复合新技术国家重点实验室, 武汉　430070

通讯作者: E-mail: xiaoleinie@whut.edu.cn.; E-mail: wyzhao@whut.edu.cn.

中图分类号: 73.50.Lw, 84.60.Rb, 85.80.Fi

xFe/Bi_0.5Sb_1.5Te₃ thermoelectromagnetic films with coexistence of positive and negative magnetoresistance

State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China

Corresponding authors: E-mail: xiaoleinie@whut.edu.cn.; E-mail: wyzhao@whut.edu.cn.

MSC: 73.50.Lw, 84.60.Rb, 85.80.Fi

摘要: 具有优异电输运性能的热电薄膜是发展高效面内散热技术的关键材料, 但是过低的电输运性能是制约其应用的重要难题. 热电磁耦合新效应是近年来发展的一种优化综合热电性能的新方法. 为了探索热电磁耦合新效应对热电薄膜电输运性能的影响机制, 本研究发展了一种球磨分散-丝网印刷-热压固化一体化成型的方法, 成功制备了一系列Fe纳米粒子作为第二相的xFe/BST/环氧树脂热电磁薄膜, 并重点研究了其热电磁耦合作用及其对电热输运性能的影响规律. 研究发现, xFe/Bi_0.5Sb_1.5Te₃ (BST)/环氧树脂热电磁薄膜中存在正、负磁阻共存的现象; BST(000l)择优取向因子与正磁阻(MR⁺)之间呈正比例关系并增加热电磁薄膜的电导率; 源于强铁磁性Fe纳米粒子局部磁矩的自旋相关散射的负磁阻(MR^–)会增加Seebeck系数. 因此, 室温附近Fe/BST/环氧树脂热电磁薄膜的功率因子高达2.87 mW/(K²·m), 与BST/环氧树脂热电薄膜相比, 提高了78%. 这些结果表明, 热电磁薄膜中正、负磁阻的共存不仅可解耦热电材料中电导率与Seebeck系数之间的耦合关系, 还可以为磁纳米粒子诱导优异热电转换性能提供新的物理机制.
- p型Bi₂Te₃基热电磁薄膜 /
- 磁各向异性 /
- 磁阻 /
- 自旋相关散射
Abstract: Thermoelectric (TE) films with excellent electrical transport property are key materials for developing efficient in-plane heat dissipation technology, but their low electrical transport property is a challenge that restricts their application. Recently, a new thermo-electro-magnetic coupling effect has been proposed to significantly improve the comprehensive TE performance. In order to explore the influence of the above effects on the electric transport property of TE films, we develop an integrated preparation method through ball milling dispersion, screen-printing and hot-pressing curing, obtaining a series of xFe/Bi_0.5Sb_1.5Te₃ (BST)/epoxy TE films in which Fe nanoparticles serve as the second phase, resulting in the thermo-electro-magnetic coupling effect , and also we study their influence on the electrothermal transport performance. The results are shown below. The positive and negative magnetoresistance are co-existent in xFe/BST/epoxy thermoelectromagnetic films; the preferred orientation factor of BST (000l) is positively proportional to the positive magnetoresistance (MR⁺), resulting in an increase of the conductivity; the spin-dependent scattering of negative magnetoresistance (MR^–) derived from the local magnetic moment of strong ferromagnetic Fe nanoparticles increases the Seebeck coefficient. Hence, the power factor of Fe/BST/epoxy thermoelectromagnetic film near room temperature reaches 2.87 mW⋅K^–2⋅m^–1, which is 78% higher than that of BST/epoxy thermoelectric film. These results indicate that the coexistence of positive and negative magnetoresistance in thermoelectromagnetic films can not only relieve the coupling relationship between conductivity and Seebeck coefficient in TE materials, but also provide a new physical mechanism for the excellent TE conversion performance induced by magnetic nanoparticles.
- p-Type Bi₂Te₃ based thermoelectromagnetic films /
- magnetic anisotropy /
- magnetoresistance /
- spin dependent scattering .

图 1 xFe/BST/环氧树脂热电磁薄膜物相组成　(a) xFe/BST/环氧树脂热电磁薄膜的XRD谱; (b) 2θ为27.8°—28.6°的放大XRD谱

Figure 1. Phase constituents of xFe/BST/epoxy thermoelectromagnetic films: (a) XRD patterns of xFe/BST/epoxy thermoelectromagnetic films; (b) the enlarged XRD patterns in the 2θ range of 27.8°–28.6°.

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图 2 xFe/BST/环氧树脂热电磁薄膜的HRTEM微观结构　(a) Fe02的HAADF-STEM像; (b)—(f) Bi, Te, Sb, Fe和O的面分布

Figure 2. Microstructures of xFe/BST/epoxy thermoelectromagnetic films from HRTEM: (a) HAADF-STEM image of Fe02; (b)–(f) corresponding elemental mappings of Bi, Te, Sb, Fe, and O.

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图 3 xFe/BST/环氧树脂热电磁薄膜电输运性能　(a)电导率和Seebeck系数; (b) 功率因子

Figure 3. Electrical transport properties of the xFe/BST/epoxy thermoelectromagnetic films: (a) Electrical conductivity and Seebeck coefficient; (b) power factor.

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图 4 xFe/BST/环氧树脂热电磁薄膜的磁各向异性　(a) 测量装置; (b) Fe00, (c) Fe01, (d) Fe02, (e) Fe03和(f) Fe04在300 K时⊥H和∥H的M-H曲线. 图(b)—(f)中右下插图是零场(H = 0)附近的M-H曲线, 所有xFe/BST/环氧树脂热电磁薄膜的M-H曲线已经进行了扣除BST/环氧树脂热电薄膜背底的数据处理

Figure 4. Magnetic anisotropy of xFe/BST/epoxy thermoelectromagnetic films: (a) Measuring setup; M-H curves of (b) Fe00, (c) Fe01, (d) Fe02, (e) Fe03, and (f) Fe04⊥H (and ∥H) at 300 K. The lower-right insets in panels (b)–(f) show the M-H curves near zero field (H = 0), the M-H curves of xFe/BST/epoxy thermoelectromagnetic films were processed by BST/epoxy films background subtraction.

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图 5 xFe/BST/环氧树脂热电磁薄膜磁阻特征　(a), (b) 1.0—2.5 T范围内, 50 K时Fe00和Fe02的MR随磁场H与面外方向夹角θ的变化曲线; (c), (d) 0—2.5 T范围内, 50—300 K时Fe00和Fe02的测量MR(MR^m)随磁场的变化曲线; (e) 50 K时Fe00和xFe/BST/环氧薄膜热电磁薄膜(Fe0x, x = 1, 2, 3, 4)的MR^m随磁场的变化曲线. MR-($ {\text{MR}}_{{\text{Fe0}}x}^{\text{m}} - {\text{MR}}_{{\text{Fe0}}x}^{+}$)和两种MR^–的拟合曲线分别显示在图(e)的下半部分, 并用虚线和颜色标注

Figure 5. Magnetoresistance characteristic of xFe/BST/epoxy thermoelectromagnetic films: (a), (b) The MR dependence of the included angle θ between the magnetic field H and the out-plane direction of (a) Fe00 and (b) Fe02 in the range of 1.0–2.5 T at 50 K; (c), (d) the magnetic field dependences of measured MR (MR^m) of (c) Fe00 and (d) Fe02 at 50–300 K in the range of 0–2.5 T; (e) the magnetic field dependences of MR^m of Fe00 and xFe/BST/epoxy flexible films (Fe0x, x = 1, 2, 3, 4) at 50 K. The MR- ($ {\text{MR}}_{{\text{Fe0}}x}^{\text{m}} - {\text{MR}}_{{\text{Fe0}}x}^{+} $) and fitting curves of two kinds of MR^– are shown in the lower half of panel (e) with the color remarks and the dotted lines, respectively.

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图 6 无MR^–的BST/环氧树脂热电薄膜的物相组成分析　(a) #0Fe00, #1Fe00, #2Fe00, #3Fe00和#4Fe00的XRD图案, 对应的压力为0, 4, 8, 12和16 MPa; (b) 在27.6°—28.5°范围内XRD谱放大图; (c) 取向因子F随烧结压力的变化曲线

Figure 6. Phase constituents and preferential orientation of BST/epoxy thermoelectricity films ignoring MR^–: (a) XRD patterns of #0Fe00, #1Fe00, #2Fe00, #3Fe00, and #4Fe00 corresponding the pressure being 0, 4, 8, 12, and 16 MPa; (b) the enlarged XRD patterns in the 2θ range of 27.6°–28.5°; (c) the pressure dependence of the F of (000l) preferential orientation of BST.

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图 7 BST/环氧树脂热电薄膜的$ {\text{MR}}_{{\text{\# }}x}^{+} $随(000l)择优取向度的变化曲线　(a) 50 K时, 不同F的BST/环氧树脂热电薄膜的测量$ {\text{MR}}_{{\text{\# }}x}^ + $随磁场的变化曲线; (b) 50 K时, 不同F的BST/环氧树脂热电薄膜的Δ$ {\text{MR}}_{{\text{\# }}x}^ + $随ΔF_#x的变化曲线, 在H = 0.5—2.5 T下, 拟合方程为$ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} = {K_0}{{\Delta }}F_\# ^y{H^2} $, 其中(K₀, y)分别是0.5 T为(30.67, 2.075), 1.0 T为(24.92, 2.049), 1.5 T为(19.79, 2.006), 2.0 T为(16.54, 1.983)和2.5 T为(13.79, 1.937); (c)拟合方程为$ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} = {K_0}{{\Delta }}F_\# ^2{H^2} $, 其中K₀是常数

Figure 7. The $ {\text{MR}}_{{\text{\# }}x}^{+} $ dependences of the (000l) preferential orientation F_#x of BST in BST/epoxy thermoelectricity films: (a) The variation of $ {\text{MR}}_{{\text{\# }}x}^ + $ with the magnetic field at 50 K in the range of 0–2.5 T; (b) the fitting correlation between ΔF_# and $ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} $ at H = 0.25–2.5 T, which is expressed as $ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} = {K_0}{{\Delta }}F_\# ^y{H^2} $, where (K_0, y) is (34.29, 2.129) for 0.5 T, (24.46, 2.021) for 1.0 T, (14.27, 1.902) for 1.5 T, (19.480, 2.063) for 2.0 T, and (16.12, 2.013) for 2.50 T; (c) $ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} = {K_0}{{\Delta }}F_\# ^2{H^2} $, where K₀ is constant.

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表 1 xFe/BST/环氧树脂热电磁薄膜的F, ΔF, MR^m, MR^–和MR⁺值

Table 1. Values of F, ΔF, MR^m, MR^–, and MR⁺ of xFe/BST/epoxy thermoelectromagnetic films.

No.	F	ΔF	0.5 T			1.0 T			1.5 T			2.0 T			2.5 T
No.	F	ΔF	MR^m	MR⁺	MR^–	MR^m	MR⁺	MR^–	MR^m	MR⁺	MR^–	MR^m	MR⁺	MR^–	MR^m	MR⁺	MR^–
Fe00	0.26	0.00	0.85	0.85	0.00	2.36	2.36	0.00	4.87	4.87	0.00	7.70	7.70	0.00	11.51	11.51	0.00
Fe01	0.31	0.05	0.30	0.86	–0.57	1.07	2.42	–1.34	2.29	4.98	–2.69	3.86	7.87	–4.01	5.70	11.75	–6.05
Fe02	0.41	0.15	0.44	1.00	–0.56	1.41	2.87	–1.50	2.84	5.86	–3.02	4.66	9.24	–4.57	6.78	13.67	–6.90
Fe03	0.38	0.12	0.73	0.94	–0.21	1.96	2.69	–0.73	3.61	5.50	–1.90	5.63	8.68	–3.06	7.93	12.89	–4.96
Fe04	0.36	0.10	0.80	0.92	–0.11	2.08	2.59	–0.51	4.30	5.31	–1.01	7.19	8.38	–1.19	10.47	12.47	–2.00

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表 2 不同样品300 K时⊥H方向的实测磁性能参数

Table 2. Magnetic properties of the ⊥H of the different samples at 300 K.

Samples	x	M_s/(emu·g^–1)	H_k/Oe	K_eff/(10⁵ erg·g^–1)	ΔE/(10⁴ erg·g^–1)	H_c/Oe	M_r/(emu·g^–1)
Fe01	0.1%	107.76	9703.48	5.23	5.94	123.65	5.42
Fe02	0.2%	122.17	14456.38	8.83	8.98	93.37	4.84
Fe03	0.3%	95.80	10700.42	5.13	7.31	78.80	1.09
Fe04	0.4%	95.12	10144.43	4.82	6.23	117.48	4.14

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表 3 BST/环氧树脂热电薄膜的F_#, ΔF_#, $ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} $和K₀的值

Table 3. Values of F_#, ΔF_#, $ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} $, and K₀ of BST/epoxy thermoelectricity films.

Sample	F_#	ΔF_#	0.5 T		1.0 T		1.5 T		2.0 T		2.5 T
Sample	F_#	ΔF_#	$ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} $	K₀	$ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} $	K₀	$ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} $	K₀	$ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} $	K₀	$ {{\Delta {\mathrm{MR}}}}_{\text{\# }}^{+} $	K₀
#0Fe00	0.26	0.00	0.00	26.99	0.00	22.91	0.00	19.59	0.00	17.04	0.00	15.35
#1Fe00	0.34	0.08	0.04	26.99	0.11	22.91	0.31	19.59	0.44	17.04	0.63	15.35
#2Fe00	0.37	0.11	0.07	26.99	0.28	22.91	0.49	19.59	0.88	17.04	1.21	15.35
#3Fe00	0.42	0.16	0.18	26.99	0.60	22.91	1.15	19.59	1.69	17.04	2.48	15.35
#4Fe00	0.46	0.20	0.28	26.99	0.95	22.91	1.83	19.59	2.85	17.04	3.96	15.35

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表 4 xFe/BST/环氧树脂热电磁薄膜在不同H中的K₁, K₂, K₃, $ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{S}}{\mathrm{D}}}^{-} $和$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{W}}{\mathrm{L}}}^{-} $值

Table 4. Values of K₁, K₂, K₃, $ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{S}}{\mathrm{D}}}^{-} $, and $ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{W}}{\mathrm{L}}}^{-} $ of xFe/BST/epoxy thermoelectromagnetic films in different H

No.	K₁	K₂	K₃	0.5 T		1.0 T		1.5 T		2.0 T		2.5 T
No.	K₁	K₂	K₃	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{S}}{\mathrm{D}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{W}}{\mathrm{L}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{S}}{\mathrm{D}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{W}}{\mathrm{L}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{S}}{\mathrm{D}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{W}}{\mathrm{L}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{S}}{\mathrm{D}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{W}}{\mathrm{L}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{S}}{\mathrm{D}}}^{-} $	$ {{\mathrm{M}}{\mathrm{R}}}_{{\mathrm{W}}{\mathrm{L}}}^{-} $
Fe00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
Fe01	56.30	0.12	0.52	–0.20	–0.37	–0.82	–0.52	–2.06	–0.64	–3.27	–0.74	–5.23	–0.82
Fe02	36.77	0.17	0.45	–0.24	–0.32	–1.02	–0.47	–2.47	–0.55	–3.94	–0.64	–6.18	–0.71
Fe03	19.10	0.20	0.23	–0.05	–0.16	–0.50	–0.23	–1.61	–0.28	–2.73	–0.33	–4.60	–0.36
Fe04	6.38	0.22	0.17	–0.00	–0.12	–0.34	–0.17	–0.81	–0.21	–0.95	–0.24	–1.73	–0.27

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1. 引　言

随着微电子集成技术的快速发展, 高效散热已成为解决高集成度微电子系统中超高热流危害突出问题的唯一选择. 基于帕尔帖效应的热电薄膜面内制冷技术有望为电子元器件高效面内散热提供有效解决方案^[1], 但目前热电薄膜太低的电输运性能是制约其在该领域应用的瓶颈^[2,3]. 热电材料的热电效率决定于无量纲热电性能优值zT = α²σT/κ, 其中α, σ, T和κ 分别是Seebeck系数、电导率、绝对温度和热导率. 电输运性能决定于功率因子α²σ. 然而, 这些参数相互耦合会导致难以通过单独调控它们获得高zT. 近年来, 在热电领域内优化载流子浓度、调整电子能带结构和增强声子散射提高zT方面已经取得了一些重要进展^[4–8], 但仍然不能满足当前商业化市场对热电材料性能的要求.

传统观点认为, 磁性杂质是降低热电性能的不利因素. 然而, 自2017年Zhao等^[9]发现磁性BaFe₁₂O₁₉纳米粒子的电子库效应可以有效抑制本征激发温度区的热电性能劣化, 超顺磁性Fe, Co和Ni纳米粒子产生的电子多重散射效应^[8]可以明显增强热电性能. 自此, 磁致增强热电性能的相关研究吸引了广大研究人员的关注. 特别是近年来, 在低温热电体系中也观察到了磁致增强热电性能现象, 如n型Bi₂Te_3-xSe_x^[10,11]和p型Bi_2-xSb_xTe₃^[12–14]. 自此, 磁致增强热电转换性能的7种热-电-磁耦合效应先后被发现并被总结^[15]. 此外, 磁性纳米粒子Co^[16]和Ni^[17]增强薄膜的电热转换性能也已先后被报道. 然而, 在所有这些磁性增强纵向热电转换性能的多学科交叉研究中, 磁性作用总是源于局部磁矩对导电电子的电荷散射. 而到目前为止, 尽管磁性引起的自旋相关散射对横向热电效应的贡献已被广泛报道, 但磁性引起的自旋相关散射如何调控纵向热电效应中电热输运行为尚不清楚^[18–22].

为揭开纵向热电效应中磁性和导电电子自旋之间的神秘面纱, 本研究在BST/环氧树脂热电薄膜中嵌入强铁磁性Fe纳米粒子作为磁性功能基元, 成功引入取向随机的局部磁矩. 输运性能研究发现, Fe/BST/环氧树脂热电磁薄膜室温附近功率因子高达2.87 mW/(K²⋅m), 远高于已报道的Bi₂Te₃-基热电薄膜的值. 磁学测试表明, Fe局部磁矩与导电电子之间的自旋相关散射增强热电磁薄膜的Seebeck系数, 高的BST(000l)择优取向增大其电导率. 此外, 在Fe/BST/环氧树脂热电磁薄膜中, 由BST(000l)择优取向诱导的正磁阻(MR⁺)与由自旋相关(SD)散射和弱局域(WL)效应诱导的负磁阻(MR^–)不仅被证明可同时存在, 还可单独剥离出对应的贡献值. 本研究不仅揭示了BST(000l)择优取向因子与MR⁺之间的数学关系, 还为热电磁薄膜内自旋相关散射的存在提供了实验上的证据, 更好地完善了热电磁耦合效应的物理机制.

2. 实　验

热电磁浆料制备. 按一定比例称量BST粉、铁粉、环氧树脂、固化剂、催化剂和稀释剂, 并按以下步骤制备可印刷热电磁浆料: 1) BST铸锭被手工粉碎、筛选(120目)获得BST粉末; 2)用行星式球磨机制备系列片状xFe/BST复合粉(x = 0, 0.1%, 0.2%, 0.3%和0.4%), 商用Fe纳米粒子尺寸约为100 nm; 3)用机械搅拌器混合xFe/BST粉末、双酚F的二缩水甘油醚(环氧树脂)、甲基六氢苯酐(固化剂)、2-乙基–4-甲基咪唑(催化剂)和丁基缩水甘油醚(稀释剂); 4)超声分散前述有机/无机复合浆料, 得到均匀的可印刷xFe/BST/环氧树脂热电磁浆料.

Fe/BST/环氧树脂薄膜制备. 采用丝网印刷方法, 将xFe/BST/环氧树脂热电磁浆料印刷在厚度约为125 μm的聚酰亚胺衬底上, 形成制备xFe/BST/环氧树脂热电磁薄膜; 鼓风干燥后, 再采用自制的热压设备对热电磁薄膜进行热压固化处理, 得到BST晶粒具有(000l)择优取向的xFe/BST/环氧树脂热电磁薄膜, 其中单臂薄膜的厚度约为60 μm, 尺寸为4.0 mm×20.0 mm×0.06 mm, 且薄膜表面具有明显的金属光泽. 为了表述方便, 后文将Fe-NPs掺入量为x = 0, 0.1%, 0.2%, 0.3%和0.4%的xFe/BST/环氧树脂热电磁薄膜分别命名为Fe00, Fe01, Fe02, Fe03和Fe04. 此外, 为探索Fe引起的(000l)择优取向对xFe/BST/环氧树脂热电磁薄膜正磁阻(MR⁺)的贡献, 本研究通过改变压力获得不同的择优取向因子(F)值, 制备了一系列可以忽略负磁阻(MR^–)的BST/环氧树脂热电薄膜, 压力分别为0, 4, 8, 12和16 MPa的相应样品分别被命名为#0Fe00, #1Fe00, #2Fe00, #3Fe00和#4Fe00.

xFe/BST/环氧树脂热电磁薄膜的物相组成采用粉末X射线衍射仪(XRD, SmartLab, Rigaku Corporation, Tokyo, Japan)测试, 所用Cu-K_α波长为λ = 0.154186 nm. 采用赛默飞尔双像差校正透射电子显微镜(HRTEM, Titan Themis G2 60-300, Thermo Fisher, Oregon, USA)在300 kV下表征样品的微观结构, HRTEM样品采用聚焦离子束系统(FIB, Helios NanoLab G3 UC, Thermo Fisher, Oregon, USA)制备. xFe/BST/环氧树脂热电磁薄膜在室温的Seebeck系数α和电导率σ采用标准四探针法(CTA-3, 北京柯锐欧科技有限公司)在氦气环境下同步测量, 其中σ测量误差为±(5%—7%), α测量误差约为±5%. 采用多功能振动样品磁强计(VSM, VersaLab, Quantum Design INC., California, USA)测量不同温度、不同放样角度下磁化曲线(M-H)、高磁场下磁电阻(MR)曲线.

4. 结　论

为揭开纵向热电效应和磁阻效应之间的神秘面纱并提高热电磁薄膜的电热输运性能, 本研究利用Fe纳米粒子(Fe-NPs)消耗BST晶粒表面吸附氧, 使部分Fe-NPs发生原位氧化反应生成FeO化合物, 这有效遏制了BST的氧化, 抑制了热电磁薄膜电热输运性能的降低; 同时为借助额外磁性散射提高热电磁薄膜的电热输运性能, 在BST/环氧树脂(EP)柔性热电薄膜中嵌入了由强铁磁性Fe-NPs和弱铁磁性FeO化合物组成的磁性功能基元(MFEs), 成功引入取向随机的局部磁矩, 最终本研究采用丝网印刷结合热压固化工艺制备了一系列p型xFe/BST/环氧树脂热电磁薄膜(x = 0, 0.1%, 0.2%, 0.3%和0.4%). 微观结构表征表明, 部分Fe纳米粒子与BST晶粒表面的吸附氧发生原位氧化反应生成Fe₃O₄, 阻止了Fe与BST发生反应; Fe作为第二相对BST基体晶体结构没有影响, xFe/BST/环氧树脂热电磁薄膜中BST晶粒(000l)择优取向因子随Fe增加而先增后降. 性能测试结果表明, 随着Fe增加, xFe/BST/环氧树脂热电磁薄膜的空穴浓度降低, Seebeck系数先增后降; BST晶粒(000l)择优取向因子先增后降, 但均大于BST/环氧树脂热电薄膜的, 导致载流子散射减弱, 迁移率先升后降, 电导率先增后降, 因此功率因子先增后降, 但均大于BST/环氧树脂热电薄膜的.

进一步研究发现, 随着Fe增加, Fe诱导的织构各向异性使xFe/BST/环氧树脂热电磁薄膜的磁各项异性能先增后降, 与载流子迁移率的演变规律一致; xFe/BST/环氧树脂热电磁薄膜中存在正、负磁阻共存的情况, 其正磁阻正比于BST晶粒(000l)择优取向因子的平方, 表明热电磁薄膜的电导率的增大是源于正磁阻的增大; 随着Fe增加, 源于Fe局域磁矩的自旋相关散射诱导的负磁阻的绝对值先升后降, 与Seebeck系数的演变规律一致, 表明热电磁薄膜的负磁阻可以增加热电磁薄膜的Seebeck系数. 因此, Fe/BST/环氧树脂热电磁薄膜的功率因子明显高于不含Fe的BST/环氧树脂热电薄膜. 在300 K时, Fe02的功率因子高达2.87 mW/(K²·m), 与BST/环氧树脂热电薄膜相比, 提高了78%. 这些结果表明, 热电磁薄膜内正、负磁阻的共存不仅可以解耦热电材料中电导率与Seebeck系数之间的耦合关系, 还可以为磁纳米粒子诱导优异热电转换性能提供新的物理机制.

参考文献 (28)

正负磁阻共存的Fe/Bi_0.5Sb_1.5Te₃热电磁薄膜

通讯作者: E-mail: xiaoleinie@whut.edu.cn.; E-mail: wyzhao@whut.edu.cn.

xFe/Bi_0.5Sb_1.5Te₃ thermoelectromagnetic films with coexistence of positive and negative magnetoresistance

Corresponding authors: E-mail: xiaoleinie@whut.edu.cn.; E-mail: wyzhao@whut.edu.cn.

计量

正负磁阻共存的Fe/Bi_0.5Sb_1.5Te₃热电磁薄膜

通讯作者: E-mail: xiaoleinie@whut.edu.cn.;

通讯作者: E-mail: wyzhao@whut.edu.cn.

English Abstract

xFe/Bi_0.5Sb_1.5Te₃ thermoelectromagnetic films with coexistence of positive and negative magnetoresistance

Corresponding author: E-mail: xiaoleinie@whut.edu.cn.;

Corresponding authors: E-mail: wyzhao@whut.edu.cn.

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