本文關鍵詞： “半晶態(tài)” 熱電材料 多元強弱化學鍵 晶格動力學 熱輸運　出處：《華東師范大學》2016年博士論文　論文類型：學位論文

【摘要】：熱電材料作為一類綠色環(huán)保的新型功能材料可以利用Seebeck效應和Peltier效應實現熱能和電能的直接轉換,是一種能源再利用的新能源材料。具有高性能的熱電材料通常需要擁有較高的電輸運性能和極低的熱導率。由于電子熱導率取決于電導率且數值相對較小,所以熱電材料中對熱導率的研究主要集中于對晶格熱導率的調控。熱輸運和晶格熱導率的傳統(tǒng)描述基于聲子間的非線性相互作用、點缺陷和微結構對聲子的散射。然而,越來越多的熱電化合物,如填充方鈷礦體系、Cu基熱電化合物(Cu3SbSe3、Cu2Se等)等,不僅表現出了反常的極低熱導率,且與溫度的依賴關系也嚴重偏離了傳統(tǒng)的晶態(tài)圖像。在理論上,這些材料表現出的熱輸運行為已顛覆了傳統(tǒng)的理解。本論文通過第一性原理方法研究了幾類具有多元強弱化學鍵共存體系的晶格動力學行為和熱輸運過程,并提出了“半晶態(tài)”的物質狀態(tài)概念。在“半晶態(tài)”化合物中,不同亞結構隨外場的變化會做出不同的響應。一類亞晶格相對穩(wěn)定,具有明顯的晶態(tài)特征；而另一類亞結構則表現出大幅度非局域的振動甚至流動的特征,使材料整體表現出“部分晶態(tài)-部分液態(tài)”或“部分晶態(tài)-部分無序”的狀態(tài)。通過分析與無序原子相關的振動模式,揭示了多元強弱化學鍵與晶格動力學、晶格熱導率之問的聯(lián)系,并通過唯象的類共振散射模型描述了“半晶態(tài)”材料Cu3SbSe3的晶格熱導率。同時,通過比較晶態(tài)材料Cu3SbSe4、CuSbSe2和“半晶態(tài)”材料Cu3SbSe3的晶格動力學行為,指出了本征結構特征對化合物簡諧和非簡諧物理參數的影響。通過第一性原理的計算并結合相關實驗,展示了低溫相Cu2Se的基本結構特征,并提出了結構家族和超結構的存在。在低溫相Cu2Se中,“部分有序”(準fcc-Se原子框架)和“部分無序”(來自不同結構單元的Cu原子)的亞結構共存,使α-Cu2Se處于“半晶態(tài)”的材料狀態(tài)中。對于Cu2Se的相變過程,各低溫相結構單元直接向立方相轉變,展現出了不唯一的多形態(tài)相變路徑。對“半晶態(tài)”材料狀態(tài)的研究有助于融合晶態(tài)、非晶態(tài)和液態(tài)材料的理論研究,并為探索和設計具有極低晶格熱導率的高性能熱電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 偽 -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.
【學位授予單位】：華東師范大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O469

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