“半晶态”材料的晶格动力学行为和热输运过程

发布时间：2018-02-04 09:50

本文关键词： “半晶态” 热电材料多元强弱化学键晶格动力学热输运　出处：《华东师范大学》2016年博士论文　论文类型：学位论文

【摘要】：热电材料作为一类绿色环保的新型功能材料可以利用Seebeck效应和Peltier效应实现热能和电能的直接转换,是一种能源再利用的新能源材料。具有高性能的热电材料通常需要拥有较高的电输运性能和极低的热导率。由于电子热导率取决于电导率且数值相对较小,所以热电材料中对热导率的研究主要集中于对晶格热导率的调控。热输运和晶格热导率的传统描述基于声子间的非线性相互作用、点缺陷和微结构对声子的散射。然而,越来越多的热电化合物,如填充方钴矿体系、Cu基热电化合物(Cu3SbSe3、Cu2Se等)等,不仅表现出了反常的极低热导率,且与温度的依赖关系也严重偏离了传统的晶态图像。在理论上,这些材料表现出的热输运行为已颠覆了传统的理解。本论文通过第一性原理方法研究了几类具有多元强弱化学键共存体系的晶格动力学行为和热输运过程,并提出了“半晶态”的物质状态概念。在“半晶态”化合物中,不同亚结构随外场的变化会做出不同的响应。一类亚晶格相对稳定,具有明显的晶态特征；而另一类亚结构则表现出大幅度非局域的振动甚至流动的特征,使材料整体表现出“部分晶态-部分液态”或“部分晶态-部分无序”的状态。通过分析与无序原子相关的振动模式,揭示了多元强弱化学键与晶格动力学、晶格热导率之问的联系,并通过唯象的类共振散射模型描述了“半晶态”材料Cu3SbSe3的晶格热导率。同时,通过比较晶态材料Cu3SbSe4、CuSbSe2和“半晶态”材料Cu3SbSe3的晶格动力学行为,指出了本征结构特征对化合物简谐和非简谐物理参数的影响。通过第一性原理的计算并结合相关实验,展示了低温相Cu2Se的基本结构特征,并提出了结构家族和超结构的存在。在低温相Cu2Se中,“部分有序”(准fcc-Se原子框架)和“部分无序”(来自不同结构单元的Cu原子)的亚结构共存,使α-Cu2Se处于“半晶态”的材料状态中。对于Cu2Se的相变过程,各低温相结构单元直接向立方相转变,展现出了不唯一的多形态相变路径。对“半晶态”材料状态的研究有助于融合晶态、非晶态和液态材料的理论研究,并为探索和设计具有极低晶格热导率的高性能热电材料提供新的研究思路和方法。
[Abstract]:Thermoelectric materials, as a new kind of green functional materials, can use Seebeck effect and Peltier effect to realize the direct conversion of heat energy and electric energy. Thermoelectric materials with high performance usually require high electrical transport performance and very low thermal conductivity. Because the electronic thermal conductivity depends on the conductivity and the value is relatively small. Therefore, the study of thermal conductivity in thermoelectric materials mainly focuses on the regulation of lattice thermal conductivity. The traditional description of thermal transport and lattice thermal conductivity is based on the nonlinear interaction between phonons. However, there are more and more thermoelectric compounds, such as Cu3SbSe3Cu2Se, which is a Cu-based thermoelectric compound filled with galactonite. It not only shows abnormal very low thermal conductivity, but also deviates from the traditional crystal image seriously. The thermal transport behavior of these materials has overturned the traditional understanding. In this paper, the lattice dynamics and thermal transport processes of several kinds of systems with multivariate strong and weak chemical bonds are studied by first-principle method. The concept of "semicrystalline state" is put forward. In "semicrystalline" compounds, different substructures respond differently with the change of external field. A class of sublattices is relatively stable and has obvious crystal state characteristics. The other substructures exhibit the characteristics of large nonlocal vibration and even flow. By analyzing the vibrational modes related to the disordered atoms, the multivariate strong and weak chemical bonds and lattice dynamics are revealed. The lattice thermal conductivity of the semicrystalline material Cu3SbSe3 is described by the phenomenological quasi-resonance scattering model, and the lattice thermal conductivity of the semicrystalline material Cu3SbSe3 is also compared with that of the crystalline material Cu3SbSe4. Lattice dynamics behavior of CuSbSe2 and Cu3SbSe3. The effect of intrinsic structural characteristics on the physical parameters of simple and anharmonic compounds is pointed out. The basic structural characteristics of low-temperature phase Cu2Se are demonstrated by first-principle calculation and related experiments. The existence of the structure family and superstructure in the low temperature phase Cu2Se is also proposed. The substructures of "partially ordered" (quasi-#en0# atomic framework) and "partially disordered" (Cu atoms from different structural units) coexist. The 伪 -Cu2Se is in the "semicrystalline" state. For the phase transition process of Cu2Se, the low temperature phase structure units are transformed directly to the cubic phase. The study of the "semi-crystalline" material states is helpful to the theoretical study of the fusion of crystalline, amorphous and liquid materials. It also provides a new research idea and method for exploring and designing high performance thermoelectric materials with very low lattice thermal conductivity.
【学位授予单位】：华东师范大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O469

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