【作者】 陈龙；

【导师】 朱永春； 吴长征；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2024， 硕士

【摘要】 目前全球正面临着能源短缺、环境污染和温室效应等一系列问题,除了开发可再生能源替代传统化石能源,对能源使用过程中的能量耗散进行管理也同样重要。不论是减少工业和建筑等领域的能量耗散,还是废热转化,低热导率材料在能源管理应用中都具有重要作用。因此,开发具有低热导率的材料或限制材料中的热输运过程具有重大现实意义。二维材料因其具有特殊的结构和奇特的性质而具有广泛的应用。在热输运调控方面,二维材料特有的层状结构赋予其特殊的声子行为一一层间弱键合力软化声子,因而具有比层内更低的热导率。本论文选取二维材料作为研究框架,结合传统的热输运调控手段,在原子和分子尺度上对二维材料的结构进行设计,并限制声子的输运,进一步了降低二维材料的热导率,突破了传统热绝缘极限。本论文的具体内容包含下面两个方面:1.作者提出了一种用大质量的Bi和Ag原子共掺杂层状结构SnS的电荷平衡策略,将Ag在SnS中的掺杂极限从2%提高到3%。Ag和Bi共掺杂增加了点缺陷浓度,同时引入了丰富的边界,使声子在原子尺度和纳米尺度上受到强烈散射,极大降低了热导率。Ag0.03Bi0.03Sn0.94S在室温下的热导率低至0.535 W m-1 K-1,并在275℃时下降到了 0.388 Wm-1K-1,低于SnS非晶极限0.450 Wm-1K-1。通过简单的重原子电荷平衡掺杂策略,实现低于非晶极限的超低热导率,为追求低热导率提供了新的思路。2.作者采取了一种简单的表面修饰策略,利用PVP分子对BiOCl进行表面修饰,降低层状结构BiOCl的热导率。BiOCl由于其本征层状结构而呈片状,在合成过程中,作为表面活性剂的PVP分子会降低BiOCl纳米片厚度;同时附着在纳米片表面,并诱导表面氧空位产生。纳米片厚度变薄减少了热输运中长波声子的贡献,氧空位使到达表面的声子受到点缺陷的散射,减少了载热声子对热导率的贡献。表面形成的有机-无机界面由于结构和键合方式的差异产生了界面热阻。基于这些原因,表面修饰PVP的BiOCl热导率相较于BiOCl下降了 36%,在室温下低至0.229Wm-1 K-1。本工作为二维材料热导率调控提供了一种分子表面修饰方法。更多还原

【Abstract】 The world is facing a series of problems such as energy shortage,environmental pollution and greenhouse effect.In addition to developing renewable energy to replace traditional fossil energy,it is equally important to manage the energy dissipation in the process of energy use.Whether it is to reduce energy dissipation in industries and buildings,or to convert waste heat,low thermal conductivity materials play an important role in energy management.Therefore,it is of great practical significance to develop materials with low thermal conductivity or to restrict the heat transport process in materials.Two-dimensional materials are widely used because of their special structure and peculiar properties.In terms of heat transport regulation,the unique layered structure of two-dimensional materials gives them a special phonon behavior-the weak bonding force between layers softenes the phonons,so they have lower out-of-plane thermal conductivity than the in-plane.In this paper,two-dimensional materials are selected as the research framework,combined with traditional thermal transport control methods,and multi-scale restrictions on phonons in two-dimensional materials are carried out by using point defects,grain boundaries and heterogeneous interfaces,further reducing the thermal conductivity of two-dimensional materials,breaking through the traditional thermal insulation limit,and establishing a new phonon transport model.The specific content of this paper includes the following two aspects:1.The author proposed a charge-balance strategy for co-doping SnS with heavy Bi and Ag,which increases the doping limit of Ag in SnS from 2%to 3%.Ag and Bi co-doping increase the point defect concentration,and introduce rich boundaries,so that phonons are strongly scattered at the atomic scale and nanoscale,and greatly reduce the thermal conductivity.The thermal conductivity of Ag0.03Bi0.03Sno.94S is as low as 0.535 W m-1 K-1 at room temperature and drops to 0.388 W m-1 K-1at 275℃ which is lower than the SnS’s amorphous limit of 0.450 W m-1 K-1.Through a simple charge balance doping strategy of heavy atoms,the ultra-low thermal conductivity below the amorphous limit is achieved,which provides a new way to pursue low thermal conductivity.2.The author adopted a simple surface modification strategy,using PVP molecules to modify the surface of BiOCl and reduce the thermal conductivity of BiOCl.The thickness of BiOCl nanosheets was reduced by PVP molecules as surfactants during the synthesis process.At the same time,it is attached to the surface of the nanosheet and induces the formation of surface oxygen vacancy.The thinner thickness of nanosheets reduces the contribution of long-wave phonons in heat transport.And the phonons at the surface are scattered by point defects due to oxygen vacancies,and the organicinorganic interface formed on the surface has thermal resistance due to the difference in structure and bonding.For these reasons,the thermal conductivity of BiOCl modified by PVP decreased by 36%compared to BiOCl,and was as low as 0.229 W m-1 K-1 at room temperature.This work provides a surface modification method for thermal conductivity control of two-dimensional materials.更多还原