由於鈦酸鉛具有優異的機電性質以及鐵電性質，其固溶體如Pb(Zr, Ti)O3 (PZT) 和Pb(Mg1/3, Nb2/3)O3-PbTiO3 (PMNPT)等等…，已經被廣泛使用在科技產品上，像是微致動器(micro-actuator)，傳感器(sensors)，與隨機存取記憶體(nonvolatile random access memories,FeRAMs)等等…。鈦酸鉛在無添加電場情況下便具有自發極化量，對於這種材料而言，輕微的原子位移變化便會顯著影響機械特性以及鐵電特性，因此，深入的在原子尺度下了解鐵電材料行為是必要的。另外，鐵電材料的電域以及電域壁的性質在近年來引起大量的關注，具電域壁之鐵電體能增大光伏效應產生之電壓，提升效率，且電域壁可隨著電場的作用下發生改變，可以運用在可擦除式記憶體，然而，電域翻轉以及電域壁移動皆在皮秒(ps)~毫秒(ms)之內發生，實驗上難以觀測，因此需藉由電腦分子動力學模擬研究，來分析電域壁在原子級之資訊。
本研究成功開發了新的殼核模型參數來模擬鈦酸鉛之原子間作用力，而新參數由擬合第一原理計算之鈦酸鉛晶體結構、彈性常數、聲子振動頻率等等…，並且通過使用新參數來進行分子動力學模擬來驗證參數的合理性以及在有限溫度下的預測能力，且模擬出鈦酸鉛從四方體轉變至立方體之相轉變過程，相轉變溫度為697 K，略低於實驗值760 K。此外，使用新參數勢能模擬奈米尺度下180度電域壁和90度電域壁，在不同溫度下電域大小以及界面對電域壁的穩定性，並且找出在不同溫度下，電域壁能穩定存在之最小電域大小，隨後更進一步的施加均勻電場，觀測電域在電場的作用下之反應。

Due to its outstanding electromechanical properties, lead titanate (PbTiO3) and it’s solid solutions, such as Pb(Zr,Ti)O3 (PZT) and Pb(Mg1/3,Nb2/3)O3-PbTiO3 (PMNPT), have been widely applied in technological devices like non-volatile random access memories (FeRAMs), micro-actuator and sensors[1-7]. For such materials, a slight atomic displacement strongly affects both mechanical and ferroelectric (FE) properties. Thus, a proper understanding of the atomic behavior of ferroelectrics is required. Computational simulation is a promising tool for analysis of the properties above. In this study, we have successfully reparameterized the core-shell model to model PbTiO3. The new parameters considered the crystal structures, elastic properties and phonon frequencies which calculated by ab-initio density functional theory calculations. Moreover, the new parameters were also tested by molecular dynamics simulations to examine the predictive ability at finite temperature. The phase transition temperature of 697 K from the tetragonal to the cubic phase was obtained, which is 63 K underestimated compare with the experimental results, 760 K. Furthermore, the new model was then used to study the interfacial effect on ferroelectricity at the nanoscale. The critical size of domain of the ferroelectric domains which can be stabilized the 180 domain wall at various temperatures in bulk and thin film are concerned. Found that the stabilized of the domain wall is depend on the difficulty of polarization reversed. From the simulated models, a deeper understanding of the domain motion in atomic scale was achieved.

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