论文信息

研究背景

热电材料作为一种能够实现热能与电能直接转换的固态能源材料，在芯片制冷、深空探测以及智能能源系统等领域具有重要应用价值。然而，热电转换效率受到载流子与声子输运耦合作用的限制。近年来，缺陷调控、合金化以及界面工程等策略被广泛用于优化热电性能，但现有研究主要关注局域散射效应，忽略了结构单元间的空间连通性对整体输运行为的影响。在多种热电材料中，成分偏析、晶界富集及局域成分波动等化学不均匀现象普遍存在，其通常被认为可通过增强缺陷和界面散射降低晶格热导率。然而，当非均匀结构形成连续空间连接时，可能产生区别于传统局域散射的输运调控效应，并显著影响载流子与声子传输。因此，揭示化学不均匀结构空间分布与热电输运行为之间的关联，对于理解微观结构调控机制和提升热电材料性能具有重要意义。

文章概述

大连理工大学王同敏教授和康慧君教授研究团队联合哈尔滨工业大学刘明副研究员报道了一种通过循环压力烧结调控空间连通的化学不均匀结构的策略，揭示了化学不均匀结构的空间连通性对热电输运行为的影响机制。研究发现，Mg₃(Sb, Bi)₂热电材料中广泛存在的多尺度Bi相关化学不均匀结构可形成空间连通的渗流网络，诱发寄生输运通道，从而降低泽贝克系数并削弱材料的低热导优势。通过引入循环压力烧结工艺调控Bi元素分布，有效破坏了化学不均匀结构形成的连续渗流网络，抑制寄生输运行为，使Mg_3.2Sb_1.5Bi_0.49Te_0.01在723 K实现1.82的热电优值。进一步添加Cu元素后，材料在673 K实现约2.08的热电优值，并在323至723 K的宽温区内实现约1.58的平均热电优值。此外，基于优化材料构建的单腿热电器件在410 K的温差下实现了约12.1%的转换效率。

图文导读

(1) 压力驱动的化学均匀化策略：通过调控烧结过程中的压力演变，实现对空间连通的成分波动和偏析结构的有效调节，抑制由化学不均匀性引起的寄生输运行为，从而优化载流子与声子输运。基于该策略制备的Mg₃(Sb, Bi)₂材料展现出优异的热电性能，在不同制备工艺中具有显著竞争优势。

FIGURE 1 Pressure-driven chemical homogenization leading to high TE performance. (a) Schematic illustration of chemical fluctuation regulation via pressure-modulated sintering. (b) Schematic illustration of the detrimental impact of chemical fluctuations. (c) Comparison of zT in Mg₃(Sb, Bi)₂-based materials processed using different strategies.

(2) 化学非均匀性调控：通过EBSD、EPMA、TEM-EDS和APT等多尺度表征发现，恒压烧结样品中存在连续Bi晶界偏析网络及晶内成分波动，而循环压力烧结有效调控了Bi空间分布，将连续偏析网络转变为孤立纳米Bi相，并抑制晶内Bi成分起伏，实现化学非均匀结构的控制。

FIGURE 2 Microstructural and compositional comparison of Mg3(Sb, Bi)2 consolidated under constant and variable pressure. (a) EBSD orientation map, and (b) Kikuchi band contrast map (red lines indicate low-angle grain boundaries) of the CP-50 sample. (c) EBSD orientation map, and (d) Kikuchi band contrast map (red lines indicate low-angle grain boundaries) of the VP-20 sample. (e) EPMA mapping of Bi in the CP sample, revealing pronounced compositional heterogeneity. (f) TEM image and corresponding EDS map in the CP-50 sample showing continuous Bi phases and Bi segregation along grain boundaries. (g) EPMA mapping of Bi in the VP-20 sample, indicating a more homogeneous elemental distribution. (h) TEM image and corresponding EDS map in the VP-20 sample showing isolated Bi phases at grain boundaries. (i) High-resolution imaging of intragranular regions of the CP-50 sample, revealing pronounced chemical fluctuations. (j) APT reconstruction (20 at. % isosurface) showing nanoscale Bi-rich fluctuations in the CP sample. (k) High-resolution imaging of intragranular regions of the VP-20 sample, revealing suppressed compositional fluctuations. (l) APT reconstruction (20 at. % isosurface) showing a uniform atomic-scale elemental distribution in the VP sample.

(3) 寄生泽贝克效应：空间均匀样品在323 K实现了约- 220 μV K^-1的高泽贝克系数。结合载流子分析、DFT计算及C-AFM表征发现，连续Bi成分波动可形成快速载流子传输通道，使具有低泽贝克系数和高电导率的Bi富集区域对整体输运贡献增加，从而引入负向寄生泽贝克效应。循环压力烧结通过消除连续成分波动，有效抑制该寄生效应，实现泽贝克系数提升。

FIGURE 3 Electrical transport properties. (a) S. (b) PF. (c) n_H for CP-50, VP-10, and VP-20 samples. (d) Top: depiction charges transfer at the interface between Mg₃Bi2 and Mg₃Sb_1.5Bi_0.5. Bottom: Planar-averaged charge density difference (Δρ) along the Z direction. “Without barrier” indicates the case without an inserted potential barrier. (e) S and σ as a function of carrier concentration for n-type Mg₃Sb₂ and Mg₃Bi₂ at 300K. (f) Current mapping generated by C-AFM at a 0.1 V bias voltage for the CP-50 sample. (g) Schematic of the parasitic Seebeck effect. Under a temperature gradient, both the matrix and the precipitates generate electrons. Electrons originating from precipitates with a lower S are fewer in number but transport faster, thereby enhancing their contribution to the overall Seebeck response.

(4) 热电性能与器件性能验证：连续Bi晶界相的破坏有效降低了晶格热导率，结合Cu元素调控进一步提升了Mg₃(Sb, Bi)₂材料的热电性能，实现了673 K下约2.08的热电优值，并在323至723 K宽温区获得约1.58的平均热电优值。基于优化材料构建的单腿热电器件的转换效率（12.1%）与目前代表性中温热电材料的器件转换效率相当，展现出良好的实际热电转换应用潜力。

FIGURE 4 Thermoelectric properties and single-leg device performance. (a) Temperature-dependent κ_l for CP-50, VP-10, and VP-20 samples. (b) Temperature-dependent zT for CP-50, VP-10, and VP-20 samples. (c) Comparison of zT values for Mg_3.2Sb_1.5Bi_0.49Te_0.01 and Mg_3.2Sb_1.5Bi_0.49Te_0.01Cu_0.01 fabricated by the VP-20 process using the literature-reported process. (d-e) Output voltage and output power, and the conversion efficiency under different temperatures. (f) Comparison of the maximum conversion efficiency at different temperature differences with representative mid-temperature thermoelectric materials.

期刊介绍

Angewandte Chemie是全球化学领域最具影响力的顶级期刊之一，由德国化学会（German Chemical Society, GDCh）出版，创刊于1887年，最新影响因子为16.9。