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系統識別號 U0026-0209201616143900
論文名稱(中文) 以多尺度模擬研究鍶含量對鍶鋇鈮陶瓷鐵電性質之影響
論文名稱(英文) Study of Sr-to-Ba Ratio Effect on Ferroelectricity of Strontium Barium Niobate by Multi-scale Simulation methods
校院名稱 成功大學
系所名稱(中) 材料科學及工程學系
系所名稱(英) Department of Materials Science and Engineering
學年度 104
學期 2
出版年 105
研究生(中文) 孫逸安
研究生(英文) Yi-An Sun
電子信箱 N56031514@GMAIL.COM
學號 N56031514
學位類別 碩士
語文別 中文
論文頁數 67頁
口試委員 指導教授-許文東
口試委員-林士剛
口試委員-齊孝定
口試委員-陳宜君
口試委員-郭錦龍
中文關鍵字 鍶鋇鈮陶瓷  弛滯體  鐵電性  第一原理  分子動力學 
英文關鍵字 Strontium barium niobate  relaxor  ferroelectric  first-principles calculation  molecular dynamic simulation. 
學科別分類
中文摘要 弛滯體因存在奈米極化區域而導致局部電極化的現象,其性質有別於一般鐵電材料,但形成機制和成因至今依然未有定論。目前較被採信的理論為弛滯體有一隨機場會影響鐵電材料的淨電極化量而導致極化電域破碎而形成奈米極化區域。而隨機場易生成於電荷分佈不平衡或空間分佈不平衡的結構中[1],而鍶鋇鈮系列材料卻能藉由相同電荷的鍶離子和鋇離子之比例控制而展現出弛滯體的特性,至今仍然沒有確切的模型可以解釋。
本研究先使用第一原理做計算,依照不同鍶含量做結構優化,並跟實驗上的數據做比對,發現八面體中鈮氧鍵長會因為鍶含量的差異和鄰近格隙陽離子而有所改變,進而影響整體結構的自發極化量。本研究也計算格隙間不同陽離子到氧離子之間的距離也都有差異,本研究認為這些差異便是影響材料性質的主要原因。接著在利用分子動力學拓展模型的原子尺度,並觀察不同鍶含量下的SBN之極化電域,並觀察格隙間陽離子之排列方式是否會影響極化電域。
英文摘要 Strontium barium niobate-based series material SrxBa1-xNb2O6 (SBN) has excellent ferroelectric properties, as well as pyroelectric and piezoelectric properties. SBN can transform from ferroelectric material to relaxor by tuning Sr/(Sr+Ba) ratio. When Sr/(Sr+Ba) ratio is 0.25 (x > 0.25), it shows normal ferroelectric behavior. As the Sr/(Sr+Ba) ratio increases from 0.6, it begins to show relaxor behavior until Sr/(Sr+Ba) ratio reaches 0.75. For Sr/(Sr+Ba) ratio above 0.8, it lost spontaneous polarization and shows no ferroelectric properties. In this study first-principles calculation was used to reveal the Sr/(Sr+Ba) ratio dependent ferroelectric properties of SBN. The structure of SBN with x = 0.4, 0.6, 0.8 were determined by special quasirandom structure (SQS) method first and then optimized by the Vienna Ab initio simulation package (VASP). The results show that Sr/(Sr+Ba) ratio will influences the deviation of Niobium ions in octahedral sites and the distance between cation and anion. Those displacements of ions are then proved to have large influence on the magnitude of spontaneous polarization; thus it is considered to be the mechanism that responsible for the Sr/(Sr+Ba) ratio dependent ferroelectric properties of SBN. Besides we also developed born model for SBN to simulate polar nanoregion by molecular dynamic simulation. It is found that pattern of polar nanoregions is closely related to Sr/(Sr+Ba) ratio in SBN.
論文目次 目錄
摘要 I
Abstract II
誌謝 VIII
圖目錄 XII
表目錄 XIV
第一章 緒論 1
1.1 前言 1
1.2 研究目的 2
第二章 文獻回顧 3
2.1 鐵電陶瓷材料 3
2.1.1 起源及介紹 3
2.1.2 鐵電性 4
2.2 鍶鋇鈮系列材料及其特性 6
2.2.1 鍶鋇鈮結構 6
2.2.2 弛滯體特性 8
2.3 電域(domain) 9
2.4 奈米極化區域(polar nano regions, PNRs) 10
2.5 隨機場(Random fields) 11
第三章 模擬基礎理論回顧 13
3.1 第一原理(First principles) 13
3.1.1 密度泛函理論(Density functional theory) 14
3.1.2 Hohenberg-Kohn定理 15
3.1.3 Kohn-Shan方法 16
3.1.4 Kohn-Sham方程式 18
3.1.5 局部密度近似法與廣義梯度近似 19
3.2 分子動力學模擬 20
3.2.1 分子動力學基本理論 20
3.2.2 運動方程式 22
3.2.3 計算效率優化 23
第四章 實驗設計 26
4.1 第一原理計算優化及ab-initio MD 26
4.2 分子動力學模擬及退火演算法 29
第五章 結果與討論 31
5.1 第一原理計算 31
5.1.1 SBN收斂驗證 31
5.1.2 SBN鬆弛測試 31
5.1.3 SBN優化結果 32
5.1.4 SBN結構計算 33
5.1.5 鈮氧鍵長比較 38
5.1.6 陽離子與氧之距離 42
5.1.7 電荷密度分析(charge density analysis) 43
5.2 分子動力學計算 45
5.2.1 分子動力學模型測試 45
5.2.2 極化電域之分佈與極化量 50
5.2.3 陽離子格隙位置排列 54
5.2.4 離子電荷分佈之影響 58
5.2.5 陽離子隔隙之角度改變 61
第六章 結論 64
第七章 參考文獻 65

圖目錄
圖2.1 介、壓、焦、鐵電性關係分佈圖 4
圖2.2 電滯曲線示意圖 5
圖2.3 SBN結構圖 8
圖2.4 (a) 90度 (b) 180度電域示意圖 10
圖3.1 第一原理自洽流程圖 17
圖3.2 分子動力學之流程圖 22
圖3.3 Verlet表列法示意圖 25
圖3.4 截斷半徑法 25
圖4.1 鍶鋇鈮之單位晶胞(SBN60) (a)俯視圖 (b)側面圖 28
圖5.1 SBN中a與c軸晶格常數與鍶含量的之關係 (a) 文獻[7] (b) 本研究之結果 33
圖5.2 (a) 鈮氧分類俯視圖 (b) 鈮氧分類側面圖[31] 39
圖5.3 SBN60鈮氧分類位置圖 39
圖5.4 文獻 (a) Nb1與鄰近氧之鍵長 (b) Nb2與鄰近氧之鍵長[31] 41
圖5.5 本模型 (a) Nb1與鄰近氧之鍵長 (b) Nb2與鄰近氧之鍵長 41
圖5.6 鋇氧距離和鍶氧距離之分佈 43
圖5.7 Ab-initio MD之SBN50能量收斂圖 46
圖5.8 Ab-initio MD之SBN60能量收斂圖 46
圖5.9 Ab-initio MD之SBN73能量收斂圖 47
圖5.10 SBN60之ab-initio MD模型圖 48
圖5.11 SBN60之MD模型圖 48
圖5.12 SBN60之ab-initio MD徑向分佈圖 49
圖5.13 SBN60之MD徑向分佈圖 49
圖5.14 不同鍶含量下之極化電域[33] 51
圖5.15 SBN50極化電域圖 (a) order (b) disorder 51
圖5.16 SBN60極化電域圖 (a) order (b) disorder 51
圖5.17 SBN73極化電域圖 (a) order (b) disorder 52
圖5.18 電荷調整流程圖 59
圖5.19 SBN50極化電域圖 (a) fixed (b) adjusted 60
圖5.20 SBN60極化電域圖 (a) fixed (b) adjusted 60
圖5.21 SBN73極化電域圖 (a) fixed (b) adjusted 60
圖5.22 Trigonal site角度分佈圖 62
圖5.23 Tetragonal site角度分佈圖 63
圖5.24 Pentagonal site角度分佈圖 63


表目錄
表2.1 鍶及鋇離子填入隔隙之機率 12
表3.1 VASP軟體之ISIF參數操作表 14
表5.1 SBN40單位晶胞之收斂驗證 31
表5.2 第一原理鬆弛方式與總能量比較(單位:eV) 32
表5.3 各組成之能量比較(a)SBN50 (b)SBN60 (c)SBN73 35
表5.4 各成分下的鈮氧鍵長 43
表5.5 不同鍶含量下各離子平均分佈電荷 44
表5.6 不同鍶含量下鈮和氧離子的平均分佈電荷 44
表5.7 不同鍶含量下各離子分佈電荷之標準差 44
表5.8 不同鍶含量下鈮和氧離子的分佈電荷之標準差 45
表5.9 Disorder和order模型的電域壁長度 52
表5.10 Order模型中各種鍶含量下SBN的極化量 54
表5.11 Disorder模型中各種鍶含量下SBN的極化量 54
表5.12 隨機結構能量圖 55
表5.13 各結構電域壁長度 55
表5.14 三種格隙陽離子隨機排列的極化電域圖 56
表5.15 各成分下的SBN之排列組合 57
表5.16 Fixed和adjusted模型的電域壁長度 61
表5.17各隔隙之平均角度 62
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