非揮發性記憶體在積體電路中是很重要的元件。鐵電材料的電偶極矩方向可隨外加電場翻轉以及電域的成長可被外加電場調控，此特性開啟了對鐵電材料的非揮發性記憶體研究。而被外加電場翻轉的區域的維持時間是個一直以來想被克服的問題，本研究即討論奈米電域在混相鐵酸鉍退極化行為，我們利用15V 100ms的脈衝電場在混相鐵酸鉍上電極化翻轉出大小約100nm的電域，再利用壓電力顯微鏡觀察奈米電域隨時間的消退，我們發現奈米電域的域壁若與混相鐵酸鉍T-like相與R-like相的相邊界呈對稱結構則可停留300個小時以上，我們用週期性彈性位能模型解釋此穩定的現象。為了使奈米電域的穩定度增加我們利用操控樣品內部帶電缺陷的方式，結果施加電場方向與混相鐵酸鉍自發極化方向相同或相反都可以增加奈米電域的穩定度。發現施加順自發性極化方向的電場效果最好，使奈米電域在混相鐵酸鉍上存活了四個月以上。本論文引入應力參數來調制電域動態行為，此概念提供非揮發性記憶元件一個新的方向。

Non-volatile memory is one of important device in integrated circuit. The spontaneous polarization and electrical doamain in ferroelectric material can be modulated by external electric field, which is the advantage for manufacturing the non-volatile memory. However, the retention of the switched domain is a key issue which has not been resolved. In our research, we discussed the polarization relaxation in mixed-phase BiFeO3(BFO). We applied 15V and 100ms pulse to switch nano-domain of size about 100nm and observed the nano-domain changing with time by Piezoresponse Force Microscopy (PFM). The symmetric structure composed by nano-domain and mixed-phase boundary causes the nano-domain to stay in a stable state and the relaxation time is larger than 300 hr. We use periodic elastic potential to explain the formation of this stable state. To enhance the retention on mixed-phase BFO, we controlled the electric defects and get a relaxation time larger than 4 months. The dynamic behavior of the domain modulated by elastic factors give a new direction to develop the non-volatile memory.

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