臺灣博碩士論文加值系統

摘要
本論文對弛豫型鐵電單晶PZN-xPT(x=0.085)與PMN-xPT(x=0.24、0.31、0.32、0.33)，沿晶體[001]方向與PMN-0.33PT沿晶體[111]方向，進行極化強度隨溫度變化的研究，並與這些晶體的介電異常量測做比較與討論；極化強度之飽和極化強度Ps與剩餘極化強度Pr，是由升(降)溫過程中，各溫度點晶體的電滯曲線量測所得。沿晶體[001]方向，由電滯曲線的量測中我們看到PT的摻入提高了這類混合晶體的矯頑電場強度Ec與極化強度Ps和Pr；由剩餘極化強度(Pr)對溫度(T)關係圖的觀察：PMN-0.24PT在溫度370 K、PMN-0.31PT在溫度390 K、PMN-0.32PT在溫度445 K、PMN-0.33PT在溫度425 K及PZN-0.085PT在溫度440 K附近，Pr呈現一階梯狀突然的改變並且也有極化的熱滯曲線顯示這些晶體在上述溫度點附近的相轉變是一階相變；另外，較低溫區域，PMN-0.31PT在溫度370 K、PMN-0.33PT在溫度360 K及PZN-0.085PT在溫度350 K附近，Pr出現一較平緩的改變 (不同於沿PMN-0.33PT[111]方向的量測，在溫度360 K，Pr亦呈現一階梯狀突然的改變)，介電異常之外加電場降溫-零電場升溫過程(FC-ZFH)的量測中，於上述溫度也有相互的對應，這呼應了先前報告對此類晶體多相性相邊界(MPB)的研究，並且這些相變也都是一階相變。而從偏光顯微鏡對PMN-0.31PT極化晶域(polar domain)隨溫度的觀察，可以知道這類混合晶體在相變溫度區間有共存相發生。

ABSTRACT
The dielectric constant and polarization-electric field (P-E) hysteresis loops have been measured as a function of temperature in relaxor ferroelectric single crystals (PbZn1/3Nb2/3O3)1-x(PbTiO3)x (PZN-xPT) for x=0.085 and (PbMg1/3Nb2/3O3)1-x(PbTiO3)x (PMN-xPT) for x=0.24, 0.31, 0.32 and 0.33. We found that the coercive field Ec and polarization of P-E hysteresis loop increases with increasing PT content. A sharp ferroelectric transition with an abrupt step-like discontinuity in polarization was observed near 370 K for PMN-0.24PT, 390 K for PMN-0.31PT, 445 K for PMN-0.32PT and 425 K for PMN-0.33PT, respectively. Both thermal hysteresis and discontinuous behavior of polarization imply a metastable state at the phase transition temperature, which can only exist theoretically for first-order transition but not second-order transitions. In lower temperature range, polarization measurement shows a small change near 370 K for PMN-0.31PT, 360 K for PMN-0.33PT and 350 K for PZN-0.085PT along the [001] direction, but an abrupt step-like change is observed for PMN-0.33PT measured along the [111] direction at 360 K. These are all diffuse first-order transitions. The field-cooled-zero-field-heated (FC-ZFH) dielectric constant also exhibits sharp anomalies correspondingly. In addition, the domain structures of PMN-0.31PT observed by polarized light microscopy confirms the phase coexistence in these type mixed crystals.

目 錄
圖表索引 i
摘要 iv
目次
1. 簡介 1
1-1. 弛豫鐵電材料 2
1-2. (PMN-XPT) 和 (PZN-XPT)混合單晶 4
2. 原理簡介 6
2-1. 電滯曲線 6
2-2. 鐵電晶體的相變理論 (Landau Theory of the Phase Transition) 8
2-2.1 二階相變(second-order transition) 9
2-2.2 一階相變(First-order transition) 10
3. 實驗裝置、原理與步驟 12
3-1. 樣品的製程 12
3-2. 樣品的製備 12
3-3. 實驗裝置與原理：(Sawyer-Tower 電路) 12
4. 結果與討論 17
4-1. 單晶PMN-xPT (x = 0.24、0.31、0.32、0.33)隨溫度變化的極化異常分析 17
4-2. 單晶PZN-0.085PT隨溫度變化的極化異常分析 20
4-3. 單晶PMN-0.31PT晶域壁(domain wall)隨溫度變化 36
5. 結論 39
參考文獻 41
近兩年學術著作發表 43

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