陶瓷介電電容有極高的功率密度(~108 W kg-1 )、極短的放電時間(~1 μs)、很高的溫度穩定性及多次的循環壽命(~105 cycle)的優勢，目前具有前景的應用有離子加速器、雷射武器、電漿系統、油電車等超高功率系統。本實驗的(1-x)(0.3BiFeO3-0.7SrTiO3)-xK0.5Na0.5NbO3(BFO-STO-xKNN, x=00.05)固溶體陶瓷是以固相合成法製備而成，由於BFO、STO及KNN都有各自不同的鐵電行為，希冀能透過固溶這三種鈣鈦礦結構來形成新的鈣鈦礦固溶體並研究其鐵電特性來做儲能性質之研究。對現今的儲能介電陶瓷而言如果想要有好的儲能能力主要致力於提高最大極化量、降低殘餘極化量以及提升介電崩潰電場。從XRD的結果可以發現BFO-STO-xKNN(x=00.05)在1150℃的空氣中燒結兩個小時後，其均為純相立方晶系的鈣鈦礦結構，並藉由Rietveld法精算結構後，發現隨著KNN的加入一開始晶格常數會先變小再變大，先變小的原因是由於少量KNN的加入消除了氧空缺所造成的晶格膨脹，而後來變大的原因是由於KNN中A-site位置的Na+、K+以及B-site位置的Nb5+的離子半徑較固溶體BFOSTO中A-site位置的Bi3+、Sr2+以及B-site位置的Fe3+、Ti4+的離子半徑大，所以摻入過量更大的離子使晶格常數變大。從SEM圖可以發現所製備的陶瓷十分緻密且和阿基米德法所測量的結果(相對密度約在93.4%)呼應。除了觀察晶貌，本實驗亦探討晶粒大小，從結果可以發現x=00.01時晶粒會變大，原因是x=0.005跟x=0.01消除了氧空缺所造成的晶格膨脹應力所以使得晶粒成長更容易，而x=0.010.05晶粒會慢慢變小的原因是摻入過多半徑較大的離子造成晶格扭曲嚴重使晶粒成長越發不易。從介電阻抗分析來看可以發現x=0的介電行為為Maxwell-Wagner (M-W)效應且從阻抗分析所做出的colecole plot來做活化能的擬合可以發現x=0的DC直流導電性是來自晶粒本身有Fe2+及Fe3+的存在造成電子在傳輸過程出現跳躍(hopping)。加入KNN後(i.e. x=0.01)的介電行為為Debye的模型，由於relaxation peak在大於106 Hz的位置且虛部讀值在低頻遠小於x=0的結果，說明了沒有Fe2+及Fe3+之間的電子跳躍，所以DC直流導電性很小。在儲能的應用性方面x=0.01時表現出最好的應用前景，儲能密度(Wrec)可以達到3.20 J/cm3，儲能效率(η)可以達到 88.0%，最大崩潰電場(Eb)可以達到273 kV/cm。除了儲能密度及效率外，本實驗為了考慮其在儲能領域的應用性並將x=0.01的陶瓷電容做疲勞測試、頻率測試及熱穩定性測試。在疲勞測試中使用150 kV/cm電場，經過104次循環過後大極化量從25.84 μC/cm2 下降至25.67 μC/cm2，殘餘極化量從1.95 μC/cm2 上升至2.03 μC/cm2相差幅度甚小，所以證明循環壽命極佳。在對頻率的敏感度測試中使用150 kV/cm電場，從201000 Hz的儲能密度及效率僅相差3.2% 及6.5%，也說明對不同頻率的響應相差不大。在熱穩定性的測試中在100 kV/cm電場下，溫度在25ºC的儲能密度及效率僅相差4.0% 及0.8%，也說明熱穩定性很好，使得此介電陶瓷得以在高功率領域中做應用。在陶瓷電容充放電實驗中得知x=0.01的陶瓷電容在串聯200 Ω的電阻時，在100 kV/cm 的電場下在大約35 ns 即可達到最大放電電流，t0.9在100 kV/cm的電場下的放電時間僅需333ns，經由上述的實驗可以得知x=0.01可以在陶瓷電容的領域中有良好的應用潛力。

(1-x)(0.3BiFeO3-0.7SrTiO3)-xK0.5Na0.5NbO3 (BFO-STO-xKNN, x=0–0.05) ceramics were synthesized by solid-state sintering for energy storage application. The lattice parameter of BFO-STO-xKNN decreased initially with KNN addition and then increased as x increased further. The initial decrease was explained by the reduced chemical expansion associated with oxygen vacancies, while the latter increase was caused by doping larger sizes of ionic. In contrast, the grain size of BFO-STO-xKNN initially increase due to the elimination of structural distortion caused by oxygen vacancies, while the latter decrease was due to large strain making gain growth more difficult. The samples without KNN exhibited a finite DC conductivity due to electric hopping between Fe2+ and Fe3+, while the samples with tiny KNN can obviously reduce DC conductivity. The samples with KNN exhibited slim hysteresis loops, which were useful for energy storage application. The highest recoverable energy density (Wrec) can achieved 3.20 J/cm3 and the efficiency was 88.0% with the x=0.01 samples at applied electric field of 273kV/cm. The x=0.01 samples also exhibited good thermal stability, frequency sensitivity, cycle life. The x=0.01 samples also showed fast t0.9 (333ns). This work showed x=0.01 had good potential for energy storage application.

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