一瞥知冷暖:看化學式,判熱導率

    熱導率是材料最基本的物理性能之一，決定了材料的應用方向和領域，在熱電能量轉換、熱障塗層等領域，熱導率更是核心參數之一；同時，材料的熱導率取決於從原子/晶格到晶粒等幾乎全尺度的結構特徵和多種物理作用過程。因此快速判斷和預測材料的熱導率具有重要的科學意義和應用價值，同時也極具挑戰。

 三元銅/銀基硫屬化合物室溫晶格熱導率與陰陽離子數失配度的關係圖

Latticethermal conductivity (kL) atroom temperature varying with number mismatch between cations and anions (d) internary Cu- and Ag-based chalcogenides

日前，中國科學院上海矽酸研究所史迅、陳立東研究員聯合上海大學楊炯教授、上海交通大學魏天然助理教授等，以銅/銀基三元硫屬化合物為示範，基於73種材料的晶格熱導率（kL）數據和晶體學信息，提出了快速預測材料晶格熱導率的直觀判據——陰陽離子數失配度δ = (Ncation-Nanion)/Nanion）。作者以具有較大離子數失配的Cu4Sn7S16（d = -0.3125）複雜結構化合物為例，精細解析了材料的晶體結構和晶格振動模式，分析了低溫熱輸運性質，建立了表觀陰陽離子數失配與微觀結構畸變、晶胞複雜化以及熱導率的關聯，系統闡釋了該判據的科學內涵。接下來，作者基於此判據預測了一種結構未知的低熱導新材料Cu2Sn4S9（d = -0.33），通過實驗進行了驗證。這一簡潔直觀的離子數失配判據很好地解釋了實驗現象，篩選出了新的低晶格熱導化合物，有望進一步推廣到其他複雜化合物體系，加速篩選用於能量轉換和熱管理的新型低熱導化合物。該文近期發表於npjComputational Materials6: 81 (2020)。

Cu4Sn7S16的熱輸運性質

Thermal transport properties and crystal structure for Cu4Sn7S16 

Editorial Summary

Rapidly judge thermalconductivity from chemical formula

Thermal conductivity is one of the most fundamentalproperties of materials. Thermal conductivity of materials plays an importantrole in many fields, such as thermoelectric conversion and thermal barrier coatings. The value ofthermal conductivity is determined by nearly all-scale structuralfeatures and multiple physical processes. Rapidly judging material’s thermalconductivity is extremely important yet challenging for the applications.

Cu4Sn7S16的晶體結構和三種Cu原子的局部配位

Crystal structure of Cu4Sn7S16 and local coordination of three types of Cu atoms 

Recently, the team led by Profs. Xun Shi and Lidong Chenfrom Shanghai Institute of Ceramics, Chinese Academy of Sciences, togetherwith Prof. Jiong Yangfrom Shanghai University and Dr. Tian-Ran Wei from Shanghai Jiao TongUniversity, proposed a new practical performance indicator δ (δ= (Ncation-Nanion)/Nanion) for latticethermal conductivity (kL) in complex ternary copper andsilver chalcogenides. They examined the data of room-temperature lattice thermal conductivity and crystal structure information of 73compounds and uncovered the general trend between kL-δ. Taking Cu4Sn7S16 compound with δ= -0.3125 as acase study, the authors elaborately investigated the crystal structure,low-temperature thermal transport, and lattice dynamics, and established therelationship between the number mismatch, structural distortion and latticethermal conductivity, substantiating the scientific connotation of thisindicator. Furthermore, guided by the kL-δ diagram, a new low-kL material Cu2Sn4S9 (δ = -0.33) withunknown structure is screened and verified by experiment. Such anintuitive yet rich-connotation performance indicator provides a uniqueperspective for understanding thermal transports and is powerful forefficiently screening and designing low-kL materialsfor energy conversion and thermal management applications.This articlewas recently published in npj Computational Materials 6: 81 (2020).

Cu4Sn7S16的晶格動力學Lattice dynamics of Cu4Sn7S16

原文Abstract及其翻譯

Number mismatch between cations and anions as an indicatorfor low lattice thermal conductivity in chalcogenides (陰陽離子數失配度作為硫屬化合物低晶格熱導描述符)

Tingting Deng, Tian-Ran Wei, Hui Huang, Qingfeng Song, Kunpeng Zhao, Pengfei Qiu, JiongYang, Lidong Chen & Xun Shi 

Abstract Thermal conductivity is one of the most fundamental properties of materials with the value being determined by nearly all-scale structural features and multiple physical processes. Rapidly judging material’s thermal conductivity is extremely important but challenging for the applications. The material genome paradigm offers a revolutionary way to efficiently screen and discover materials with designed properties by using accessible indicators. But such a performance indicator for thermal conductivity is quite difficult to propose due to the existence of multiple mechanisms and processes, especially for the materials with complex structures such as chalcogenides. In this study, the number mismatch between cations and anions is proposed as a practical performance indicator for lattice thermal conductivity in complex copper and silver chalcogenides, which can be used to explain the observed experimental data and find new low thermal conductivity materials. Such a number mismatch brings about rich phenomena to affect thermal conductivity including the complication of the unit cell and the creation of chemical hierarchy, point defects, rattling modes and lone-pair electrons. It is expected that this rich-connotation performance indicator can be also extended to other complex materials to discover designed thermal conductivities.

陰陽離子數失配對熱輸運的影響示意圖

Effects of δon thermal transport.

摘要 熱導率是材料重要的基本性質之一，由近全尺度結構特徵和多物理過程確定。快速判斷材料的熱導率非常重要，但是在應用中卻一直存在很大的挑戰。材料基因組研究範式通過可獲得描述符為有效篩選和發現具有特定性質的材料提供了一種革命性的方式。但是，因為多種機制和過程的存在，這種對於熱導率的性能描述符難以建立。在本研究中，我們提出以陰陽離子數的失配度被作為複雜銅、銀硫屬化合物中熱導率的實際描述符，利用這一描述符可以解釋觀察到的實驗數據和尋找新的低熱導材料。這一描述符帶來了影響熱導率的豐富現象，包括元胞的複雜性和化學層級的建立、點缺陷、振動模式和孤對電子。這一內涵豐富的性能描述符可以被拓展到其它複雜材料，進而獲得預期的熱導率。

Cu-Sn-S體系中kL-d的關係圖

kL-ddiagram for the Cu-Sn-Scompounds

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