| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 96 === In this study, we used sol-gel method to prepare multiferroic material BiFeO3 and the bottom electrode material LaNiOx. Currently, leakage current is one of the main problems preventing BiFeO3 from practical application. Therefore, the aim of the study was to identify how the preparation parameters, such as sintering temperature, time and atmosphere, change the leakage currents of the grown films.
The experimental results showed that the LaNiOx films of highest conductivity were prepared at 700oC in air for 1hr, while pure BiFeO3 could be obtained at the temperature as low as 450 oC in flowing Ar. An impurity phase Bi2Fe4O9 (PDF card﹟72-1832) started to occur at 550 oC for a short sintering time (5 min) in Ar, but disappeared after prolonged sintering (20 min). This compound seemed to be a high temperature phase, because it persisted for a much longer sintering time(20 min) at 650 oC. This compound was more stable in higher PO2, as it still existed at 550 oC in flowing oxygen and air after sintering for 20 min.
The I-V curve measurements showed that all the films annealed in flowing Ar at 450 oC、500oC、550oC had the power law behavior, indicating the conduction mechanism might be space charge limited.
XPS analysis showed that there was a small deficiency of Bi for all the films sintered at 550 C in air, Ar and O2. This might be the main reason for the large leakage currents observed in these films, which prevented them to obtain a saturated ferroelectric hysteresis loop.
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