臺灣博碩士論文加值系統

本研究主要探討鐵電材料的光伏打特性，由於其產生的光電壓可以大於材料本身的能隙，與半導體的光伏打效應有所不同，半導體產生的光電壓不會超過p-n接面之間的能障，故有其研究的價值。但由於鐵電材料普遍為絕緣體，其電阻很大，本實驗旨在透過摻雜改善材料的導電度，並利用固相合成法簡便且易於合成之特性，製備摻雜鈦或鉬之鈮酸鉀(KNbO3:Ti/Mo)多晶塊材，觀察其極化後的光電特性。
經X射綫繞射觀察，將無摻雜之鈮酸鉀於燒結溫度800~1010°C持溫20分鐘皆可得到純相鈮酸鉀，而摻雜鈦和鉬之鈮酸鉀在燒結溫度1000°C分別持溫8和10小時可得到純相，當摻雜濃度到10%以上時，會產生第二相。摻雜鈦之鈮酸鉀在室溫下的電阻率約為7.04x108 ohm-cm，比無摻雜之鈮酸鉀(7.82x109 ohm-cm)小了約一個數量級，而摻雜鉬之鈮酸鉀，其電阻率則比無摻雜之鈮酸鉀略有增加。將試片量測其介電常數隨溫度變化之趨勢，發現摻雜鉬及鈦之鈮酸鉀的居禮溫度比無摻雜之鈮酸鉀降低約20~30°C。將試片進行極化，並嘗試不同的極化溫度、電壓及時間，以達到最佳極化效果，接著將極化之試片量測其電流-電壓綫。經實驗證實，在適當的燒結和極化條件下，所得試片可以觀察到開路電壓，照光前後有明顯的電流變化。無摻雜之鈮酸鉀在照光後並無明顯之電流增加，顯示其缺乏可被光激發的電荷載子，而摻雜鈦及鉬之鈮酸鉀在照光後之光電流均比無照光多1~2個數量級，且照光後之開路電壓均有小幅提升。

The aim of this study was to search for ferroelectric photovoltaic materials. Because ferroelectric materials usually have a very high DC resistivity over 108 ohm-cm, there is a need to increase the mobile carrier concentration in these materials. For such a purpose, KNbO3 was doped with different ions in this study. Polycrystalline samples of KNbO3:M (M=Ti and Mo) were prepared by the solid-state reaction method. X-ray diffraction showed that a pure phase of Ti or Mo doped KNbO3 could be obtained after sintering at 1000 C for 8 and 10 hours, respectively, and the doping limit was below 10 at.%, above which secondary phases occurred. The Currie temperature of KNbO3 was reduced by 20~30 C by the doping. The resistivity of KNbO3:5%Ti was measured to be 7.04108 ohm-cm, an order of magnitude smaller than the un-doped KNbO3 (7.82109 ohm-cm), whereas the Mo doped samples showed a slightly higher resistivity than the un-doped KNbO3. After electrical poling in a high field, the current-voltage curves of the samples were measured with and without light irradiation. For the un-doped KNbO3 there was virtually no change in the output current before and after the illumination, indicating a lack of the carriers that could be activated by the light. However, both Ti and Mo doped KNbO3 showed an order of magnitude increase in the output current after the illumination.

摘要 I
Abstract III
致謝 X
總目錄 XI
表目錄 XIV
圖目錄 XVI
第一章、緒論 1
第二章 理論基礎與文獻回顧 3
2-1 鐵電材料簡介 3
2-1-1 鐵電材料的特性 3
2-1-2 鐵電材料的分類 5
2-1-3 鈣鈦礦材料結構(perovskite structure) 8
2-1-4 介電性質 11
2-1-5 電滯曲線 13
2-2 電流機制 15
2-3 鐵電光伏打效應(Ferroelectric bulk photovoltaic effect) 18
2-4 鈮酸鉀材料簡介 20
2-5 置換作用 21
2-5-1 置換原理 21
2-5-2 容忍因子 22
2-6異價取代機制 24
第三章、實驗流程 35
3-1實驗材料與設備 35
3-1-1 實驗藥品 35
3-1-2 實驗設備 35
3-2 實驗流程 36
3-2-1 塊材製備 37
3-2-2 分析及量測 39
3-2-2-1 X光繞射分析 39
3-2-2-2 顯微結構觀察 39
3-2-2-3 電阻量測 39
3-2-2-4 介電性質量測 40
3-2-2-5 極化 40
3-2-2-6 I-V curve量測 41
3-3 分析儀器 42
3-3-1 X-ray粉末繞射儀 42
3-3-2高解析掃描電子顯微鏡(High Resolution Scanning Electron Microscope，HRSEM) 44
3-3-3 多功能電表 45
3-3-4 阻抗分析儀 45
3-3-5 鐵電量測系統 45
3-3-6 壓電係數量測儀 45
第四章、結果與討論 47
4-1 X-ray的成相分析 47
4-2 微觀組織及元素成分分析 54
4-3 電阻量測 62
4-4 介電性質 67
4-5極化分析 71
4-6 I-V curve特性分析 76
第五章、結論 83
參考文獻 85

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