BiFeO3(統稱BFO)具有很高的居禮溫度TC(~850℃)和尼爾溫度TN(~370℃)，在室溫下同時擁有鐵電性和反鐵磁性質，是目前最富潛力的複鐵性材料之一。但因其較大漏電流和製程產生之雜相，使其鐵電性質較差。本論文探討BFO以La和不同Cr量的共摻雜對BFO性質的影響與改變。Bi3+離子和La3+離子半徑相近，Cr3+離子和Fe3+離子半徑亦相近，故本論文希望在BFO鈣鈦礦結構中，藉由La3+離子取代Bi3+離子和Cr3+離子取代Fe3+離子來改善BFO的鐵電性質。我們利用固態反應法製作出純相BFO塊材和共摻雜La3+離子和Cr3+離子的BFO塊材，再利用XRD、SEM、XPS、電滯曲線測量、介電測量、漏電流測量來探討BFO之鐵電性。由實驗結果可以發現，Cr並不是無限固溶於BiFeO3中，當摻雜量達5%即會有明顯第二相析出。
由XPS可以發現，摻雜鑭和隨著增加量的鉻，都會使較多的Fe3+變成Fe2+，而電子可以在臨近的Fe2+和Fe3+傳導，造成導電度上升，此結果可由漏電流曲線看出，此外藉由漏電流曲線之擬和，可知道傳導機制由歐姆傳導轉成空間電荷限制傳導。介電分析可看出空間電荷為主要極化因素。

BiFeO3(BFO),which is one of the most potential multiferroics ,has high Curie temperature TC(~1123 K) and high Néel temperature TN(~643 K) resulting to the coexistence of ferroelectricity and ferromagnetism at room temperature.This study mainly reported the influence and change by the co-doping of lanthanum and different content of chromium.Bi3+ ions have close size as La3+ ions, and Fe3+ ions have close size as Cr3+ ions, so we hope to improve the ferroelectric properties with the substitution of La3+ ions for Bi3+ ions and Cr3+ ions for Fe3+ ions in the perovskite BiFeO3 structure. Bulks of BiFeO¬3 and BiFeO3 co-doping with La3+ and Cr3+ were prepared by the usual solid state reaction method. X-ray diffraction(XRD), Scanning electron microscopy(SEM), ferroelectric hysteresis measurements, leakage current measurements and dielectric measurement are used for understanding the effect of codoping. We found that second phases appeared when the doping amount of Cr were more than 5%, indicating that there was a limit for Cr doping in BFO.With the XPS analysis,La doping and the increased doping amount of Cr make more Fe ions change from Fe3+ to Fe2+,which resulting to higher conductivity by transfer of electrons between the neighboring Fe2+ and Fe3+ ions. Because of more Fe2+ ions, the conductive mechanism changes from ohmic conduction to space charge limit conduction by fitting the IV curve. The dielectric measurement can find out that the space charge is the main polarization mechanism.

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