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研究生: 沙哈許
Kondapalli Mahesh Naga Sai
論文名稱: 以第一原理計算鍍銀高熵合金導電度之研究
Study of electrical conductivity of silver-plated high-entropy alloy by first principles calculations.
指導教授: 許文東
Hsu, Wen-Dung
學位類別: 碩士
Master
系所名稱: 工學院 - 材料科學及工程學系
Department of Materials Science and Engineering
論文出版年: 2022
畢業學年度: 110
語文別: 英文
論文頁數: 61
外文關鍵詞: Electrical Conductivity, Core-Shell, Silver Paste, Frist principle calculations
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  • 高熵合金具有令人著迷的材料特性,但它們在電場中的潛力尚未得到廣泛展示。在這項研究中,高熵合金與銀一起作為核殼用於形成银浆,主要用於多層陶瓷電容器(MLCC)等電子器件。一般來說,銀具有良好的導電性,但成本很高,因此研究人員專注於尋找可以替代银浆但仍保持導電性的合成方法。在所有其他技術中,核殼法是最樂觀的方法,但核材料和殼材料之間的親和力是必不可少的。本研究以高熵合金為芯材,銀為殼材。使用反向蒙特卡羅 (RMC) 算法製作三個不同比例的 CoCrFeNi 結構。這些比例是根據元素各自的電導率制定的,它們是等比例的 Co0.25Cr0.25Fe0.25Ni0.25 和調整後的 Co0.15Cr0.35Fe0.35Ni0.15、Co0.35Cr0.15Fe0.d15Ni0.35。 Drude 和 Lorentz 模型用於計算交流電導率。我們研究了 CoCrFeNi(FCC) 和 Ag(FCC) 以及 NbMoTaW(BCC) 和 Ag(FCC) 的界面。隨後我們將銀和高熵合金的電導率與界面模型進行比較。研究方法將使用基於密度泛函理論的第一性原理計算來完成。

    Hight-Entropy alloys have fascinating material properties, but their potential in electrical fields has not been extensively exposed. In this study, the high-entropy alloys are used as a core-shell along with the silver for forming the silver paste, which is chiefly used in electronic devices like Multi-Layer Ceramic Capacitors (MLCC). Generally, silver has good electrical conductivity, but it is very costly thus researchers focus on finding the synthesis method that can replace the silver paste but still keep the conductivity. Among all other techniques, the Core-Shell method is the most optimistic method, but the affinity between the core material and shell material is indispensable. In this study, the high-entropy alloys will be used as core material and silver will be used as shell material. Three proportions of CoCrFeNi structure is made using Reverse Monte-Carlo (RMC) algorithm. These proportions are made based on the individual conductivity of the elements they are Co0.25Cr0.25Fe0.25Ni0.25 in equal ratios and adjusted Co0.15Cr0.35Fe0.35Ni0.15, Co0.35Cr0.15Fe0.15Ni0.35. The Drude and Lorentz model is used to find the AC conductivity. We have studied the interfaces of CoCrFeNi(FCC) & Ag(FCC) and also NbMoTaW(BCC) & Ag(FCC). Then we also compare the conductivity of the silver & high-entropy alloys to the interface models. The scrutiny will be carried out using density functional theory-based first-principles calculations.

    摘要 I ABSTRACT II Acknowledgement III Table of Contents IV List of Figures VI List of Tables VII Chapter 1 Introduction 1 1.1 High Entropy Alloys (HEAs) 1 1.2 Multi-Layer Ceramic Capacitors (MLCC) 2 1.2.1 Base-Metal Electrode-Multilayer Ceramic Capacitors (MLCC) 4 1.2.2 Development of Nonreducible Dielectrics for MLCCs 6 1.3 Nobel-Metal Electrode-Multilayer Ceramic Capacitors (MLCC) 6 1.4 CoCrFeNi high entropy alloy 7 Chapter 2 Literature study 8 2.1 Recent progress of high-entropy alloys 8 2.2 Concept of high-entropy alloys 8 2.3 Effects on high-entropy alloy 9 2.4 CoCrFeNi high-entropy alloy 10 Chapter 3 Methodology 11 3.1 Density Functional Theory (DFT) 11 3.1.1 First Principles Calculations 11 3.1.2 Kohn-Sham equation and Kohn-Sham potential 11 3.1.3 Approximations for exchange co-relation energy 13 3.1.4 Pseudopotentials and project augmented wave (PAW) methods 14 3.1.5 Periodic Boundary Condition (PBC) 14 3.2 Density of States (DOS) 15 3.3 Mechanical Properties 15 3.3.1 Bulk modulus from the equilibrium volume 16 3.3.2 Calculate of the elastic constants 16 3.4 Drude Model 18 3.4.1 DC filed 18 3.4.2 Time-Varying analysis 19 3.4.3 Metallic Conductivity 20 3.4.4 Optical Permittivity 21 3.4.5 Lorentz Model 22 3.5 Work of Separation and Interfacial Energy 24 3.6 Computational tools 25 3.7 Vienna Ab initio Simulation Package (VASP) 25 3.8 Material Studio 25 3.9 VESTA 25 Chapter 4 Physical Modeling and Simulation Design 27 4.1 High-Entropy alloy modeling 27 4.2 Structural Optimization parameters for CoCrFeNi high-entropy alloy 28 4.3 Making slab model of CoCrFeNi and structural optimization 29 4.4 Parameters for Frequency-Dependent Dielectric Constant Calculation 30 4.5 Interface model of Ag(FCC)_NbMoTaW(BCC) 31 4.6 Interface Model of Ag(FCC)_CoCrFeNi(FCC) 33 4.7 Structural Optimization parameters for Ag_NbMoTaW Interface 34 4.8 Structural Optimization parameters for Ag_CoCrFeNi Interface 34 Chapter 5 Results and Discussion 35 5.1 Making different compositions of CoCrFeNi models 35 5.2 Frequency dependent conductivity calculation 35 5.2.1 Frequency dependent conductivity of individual elements 36 5.2.2 Frequency dependent dielectric and conductivity of different compositions of CoCrFeNi 37 5.3 Mechanical properties of CoCrFeNi high-entropy alloy 43 5.4 Interface models of Ag(111)_NbMoTaW(110) 45 5.5 Interface models of Ag(111)_CoCrFeNi(111) 50 5.6 Interfacial energy & Work of separation of Ag_NbMoTaW, Ag_CoCrFeNi models 54 5.7 Frequency dependent dielectric constant and conductivity calculation of interfacial models. 55 Chapter 6 CONCLUSION 58 Chapter 7 REFERENCES 59

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