过渡族硫系半金属化合物的核磁共振研究

发布时间：2018-01-15 16:41

本文关键词：过渡族硫系半金属化合物的核磁共振研究　出处：《中国科学院大学(中国科学院物理研究所)》2017年博士论文　论文类型：学位论文

【摘要】：近年来,由于日益严峻的环境问题和不可再生能源的枯竭,人们开始把目光投向可再生的、对环境友好的清洁能源上。热电材料可以实现热能和电能之间的相互转化,可以有效利用生产生活等产生的废热,而且还具有相当的可靠性。因其不产生排放物也没有传动部分,因此还具有无噪声无污染的优点。对于如何提高热电材料的工作效率,在上世纪九十年代,Slack提出了声子玻璃-电子晶体(Phonon Glass Electron Crystal)的热电材料开发思路:在保持电子的传导性能的前提下降低材料的晶格热导。人们通过研究发现,在笼状(Clathrate)化合物和方钴矿(Skutterudite)结构的材料中,在其它元素形成的笼子中加入外来原子(guest atom)可以有效降低晶格热导。有观点认为这是外来原子的颤动导致了较强的晶格散射所致。近些年来,一些过渡族硫系半金属化合物被发现有优异的热电性能,被认为是一种新型的声子玻璃,其极低的晶格热导率被认为和离子的运动有关。具体来说,有研究表明离子的运动会对降低材料的晶格热导。也有研究认为离子的运动行为有液体的特征,降低了材料的热容从而导致晶格热导的降低,并由此提出了声子液体的概念。总的来说,不管是通过声子散射降低声子的平均自由程,还是降低比热容,都意味着晶格热导和原子或者离子的运动之间应当有着紧密的联系,需要有一种研究原子运动时间尺度的实验手段进行表征。核磁共振(Nuclear magnetic resonance,NMR)是一种被广泛应用的研究原子尺度结构和动力学的实验手段,在本论文中,将采用固体核磁共振技术为主要研究手段,对硫系半金属化合物模型体系进行系统的研究。论文正文将会首先详细地介绍研究背景,固体核磁共振技术和主要的实验方法。在实验结果部分,首先以过渡族硫系半金属化合物CuAgSe为研究对象,利用核磁共振技术研究原子/离子运动时间尺度的优势,从实验上给出了离子运动和晶格热导之间具有关联性的证据,并结合前人的研究结果解释了晶格热导并不随着温度单调变化的现象。随后,对不同偏分的CuAgSe样品中Cu原子的运动能力进行了追踪,提出了调节空位(Vacancy)这一新的调控离子运动能力的思路并在实验上进行了验证。最后,利用核磁共振对离子扩散的类固体(Solid-like)和类液体(Liquid-like)行为进行了研究,在实验上给出了Cu_2S体系内存在离子运动的固-液转变和固-液混合特性的证据。
[Abstract]:In recent years, due to the increasingly severe environmental problems and the depletion of non-renewable energy, people began to focus on renewable. On environmentally friendly clean energy, thermoelectric materials can realize the mutual transformation between heat energy and electricity, and can effectively utilize the waste heat generated by production and living. And it also has considerable reliability. Because it does not produce emissions or drive parts, it also has the advantage of no noise and no pollution. How to improve the efficiency of thermoelectric materials, in -10s. The phononic glass-electron crystal (Phonon Glass Electron Crystal) was proposed by Slack. The idea of developing thermoelectric materials is to reduce the lattice thermal conductivity of materials while keeping the conductivity of electrons. In materials with cage Clathrate compounds and skutterudite structures. Add a foreign atom, guest atom, to a cage made of other elements. It is believed that this is caused by strong lattice scattering due to the vibration of foreign atoms. Some transition group sulfur semimetallic compounds have been found to have excellent thermoelectric properties and are considered to be a new type of phonon glass. Their extremely low lattice thermal conductivity is considered to be related to the movement of ions. Some studies have shown that the movement of ions can reduce the lattice thermal conductivity of the materials. Some studies also show that the movement behavior of ions has the characteristic of liquid, which reduces the heat capacity of the materials and leads to the decrease of the lattice thermal conductivity. The concept of phonon liquid is proposed. In general, the average free path of phonon is reduced by phonon scattering or the specific heat capacity is reduced. It means that there should be a close relationship between lattice thermal conductivity and the movement of atoms or ions. We need an experimental method to study the time scale of atomic motion. Nuclear magnetic resonance. NMRs are widely used to study atomic scale structure and dynamics. In this thesis, solid nuclear magnetic resonance (SNMR) is used as the main research method. A systematic study on the model system of sulfur semimetallic compounds is carried out. Firstly, the research background, solid state nuclear magnetic resonance (SNMR) technology and main experimental methods are introduced in detail. Firstly, the advantage of nuclear magnetic resonance (NMR) to study the time scale of atom / ion motion is studied with the transition group sulfur semimetallic compound CuAgSe as the research object. Evidence of the correlation between ion motion and lattice thermal conductivity is given experimentally, and the phenomenon that lattice thermal conductivity does not change monotonously with temperature is explained in combination with previous studies. The movement ability of Cu atoms in CuAgSe samples with different bias was traced. A new idea of regulating the ion movement ability is proposed and verified in experiments. The behaviors of solid-like and liquid-like ions in ion diffusion have been studied by NMR. The evidence of solid-liquid transition and solid-liquid mixing in Cu_2S system is given.
【学位授予单位】：中国科学院大学(中国科学院物理研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O482.532

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