Menu

今日Science: 推进开发出极限超低热导率的材料


Pushing low thermal conductivity to the limit


Science  27 Aug 2021:

Low thermal conductivity in a modular inorganic material with bonding anisotropy and mismatch. Science 373 (6558), 1017-1022.

Summary
A wide variety of materials with low thermal conductivity find daily use, such as jackets for cold weather and plastic handles of hot metal cooking pots. Even the best thermal insulators still have a finite thermal conductivity because the vibrational motion of atoms is never fully localized and energy is transported through coherent collective vibrations (phonons). Any thermal excitation that is not fully localized can carry heat, which adds to the challenge of realizing materials with ultralow thermal conductivity for real-world applications. On page 1017 of this issue, Gibson et al. (1) have an answer to how low thermal conductivity can go. They synthesized layered inorganic bulk crystals and measured a thermal conductivity that is an order of magnitude lower than that of typical oxide glasses and only four times the value of air.
 
晶格热导率κ是所有固体固有的属性,具有重要的技术影响。电子设备需要高κ以降低热负荷,碳的同素异形体是首选材料。同位素控制是抑制携带热量的晶格振动(声子)散射的关键,用于涡轮叶片的能量收集和热障涂层的热电模块需要低κ以保持温度梯度。热导率低于石英玻璃(0.9 W K-1 m-1)的材料尤其令人感兴趣,石英玻璃用于日常隔热。晶体材料的热导率不能任意低,因为固有极限取决于声子色散。可以通过降低声子散射长度或声子群速度来减少声子热传输,其长波长极限是材料的声速。散射长度由内在(声子-声子散射,通过非谐性增强)和外在(例如,缺陷或边界散射)机制决定,而群速度由声子色散控制,声子色散是材料固有的,因为它是由结构和组成定义的。因此,许多研究已经解决了通过纳米结构和缺陷工程来减少外在声子散射长度的问题。然而,声子散射长度的下限是波长的一半,低于该值的振动不能再被视为声子。这为许多材料在高散射区接近的热导率设定了渐近高温极限。该限制本质上由整个声子色散决定,而不考虑热传导机制,并设置了所有温度下可及κ的尺度。成功的材料设计策略将通过设计由单元级结构定义的总声子色散来降低κ的渐近极限。
 
英国利物浦大学的Matthew J. Rosseinsky和Jonathan Alaria等人在Science发表最新成果,Low thermal conductivity in a modular inorganic material with bonding anisotropy and mismatch,报道了具有史上最低热导率的材料。作者使用互补策略来抑制纵向和横向声子对包含不同类型内在化学界面的层状材料中热传输的贡献。作者使用固态化学技术,在层状范德华晶体Bi2O2Cl2和Bi2O2Se以及天然超晶格Bi4O4SeCl2中合成了高度各向异性、有序无序的结构。他们没有控制材料中原子的有序性(材料工程的一种常见途径),而是操纵层间原子之间的键强度和连接性。在晶体中,与原子独立移动相比,声子模式以更高的效率引导热量。他们设计了键合模式来操纵声子的传播速度。通过调整材料的界面和晶胞的选择,他们可以选择他们的晶体允许通过的声子类型,从而产生极低的热导率。沿其堆叠方向,在室温下达到0.1 W K-1 m-1的极低热导率,该值在空气热导率的四倍以内。作者证明了对不同界面空间排列的化学控制可以协同修改振动模式以最小化热导率。这些原理应该适用于其他系统,并提供一种开发具有极低热导率的晶体的方法。

Blocking heat in two ways
Low thermal conductivity is important for barrier coatings, thermoelectrics, and other applications. Gibson et al. combined two complementary methods that manipulate internal interface properties to dramatically decrease the thermal conductivity of the inorganic material BiO2Cl2Se (see the Perspective by Kim and Cahill). The authors took advantage of both in-plane structural distortions and weak bonding layers to push the conductivity down to 0.1 watts per kelvin per meter, which is only four times that of air. The principles should be applicable to other systems and provide a method for developing crystals with extremely low thermal conductivity.

Abstract
The thermal conductivity of crystalline materials cannot be arbitrarily low, as the intrinsic limit depends on the phonon dispersion. We used complementary strategies to suppress the contribution of the longitudinal and transverse phonons to heat transport in layered materials that contain different types of intrinsic chemical interfaces. BiOCl and Bi2O2Se encapsulate these design principles for longitudinal and transverse modes, respectively, and the bulk superlattice material Bi4O4SeCl2combines these effects by ordering both interface types within its unit cell to reach an extremely low thermal conductivity of 0.1 watts per kelvin per meter at room temperature along its stacking direction. This value comes within a factor of four of the thermal conductivity of air. We demonstrated that chemical control of the spatial arrangement of distinct interfaces can synergically modify vibrational modes to minimize thermal conductivity.



Low thermal conductivity in a modular inorganic material with bonding anisotropy and mismatch. Science 373 (6558), 1017-1022.
https://science.sciencemag.org/content/373/6558/1017


 

Username:

Password:

联系我们 Contact