钙钛矿型铁电氧化物畴壁手性起源的第一原理计算研究与像差校正显微分析

As the development of the modern microelectronic industry, the dimensions of electronic devices are becoming smaller and their functions more powerful. Traditional silicon-based integrated circuits could not satisfy the requirements. The domain walls in perovskite ferroelectric oxides have two remarkable virtues for them to be designed as electronic devices used in the next-generation integrated circuits. The first is that their widths are generally in nanometer scale. The second is that they show many unexpected properties, such as conductivity, flexoelectric effect, high dielectric constant, and so on. The structures and properties of ferroelectric domain walls should be well understood at the atomic scale for them to be used as electronic devices. In this project, first-principles calculations will be used to study the origin of chiralities of domain walls of two prototypical perovskite ferroelectric oxides (PbTiO3 and BiFeO3). Various order parameters, such as ferroelectricity, ferroelasticity, antiferromagnetism, and oxygen-octahedra rotation, will be analyzed to understand the effect of order parameters on chiralities. Electronic structures of domain walls will be calculated to unravel the origin of chiralities of ferroelectric domain walls. The accurate atomic occupation and electronic structures will be determined to testify the predicted results by observing the domain walls in different orientations in the aberration-corrected high resolution transmission electron microscope. This project will not only deepen our understanding about the structures and properties of ferroelectric domain walls, but also establish the foundations for future researches, such as the possible applications of chiral ferroelectric domain walls and how to adjust the chiralities of ferroelectric domain walls, providing structural information and scientific data for the design of new electronic devices.

随着现代微电子工业的发展，电子器件有小型化和多功能化的趋势。钙钛矿型铁电氧化物中的畴壁具有尺寸小、物理性质丰富等特点，有望被设计成电子器件而应用在未来集成电路中。这些设计的基础是在原子尺度对铁电畴壁的结构和性质有充分的认识。在本项目中，申请人拟将第一原理计算作为主要研究手段，以两种典型的钙钛矿型铁电氧化物中的畴壁作为研究对象，就畴壁手性起源问题开展研究。通过考察铁电、铁弹、反铁磁、氧八面体扭转等序参量在畴壁处的变化规律，研究序参量对畴壁手性的影响规律。通过对电子结构的计算解释畴壁手性的起源。在计算结果的基础上利用像差校正透射电子显微镜从多个取向观察畴壁，对理论预测结果加以证实。该项目将丰富人们对铁电畴壁的认识，同时为进一步探索铁电畴壁手性的可能应用前景以及对铁电畴壁的手性进行调控等后续研究工作打下基础，为新型电子器件的设计与研发提供原子尺度的结构基础和科学依据。

钙钛矿型铁电氧化物中的畴壁具有尺寸小、物理性质丰富等特点，有望被设计成电子器件而应用在未来集成电路中。这些设计的基础是在原子尺度对铁电畴壁的结构和性质有充分的认识。在本项目中，我们利用第一原理计算对PbTiO3中180度畴壁的手性进行研究，发现畴壁附近布洛赫极化的形成原因是Pb离子较强的极性，为探索其他体系中可能出现的手性提供了重要的指导信息。布洛赫极化会随着面内压应变的增大而消失，使得畴壁发生手性到非手性的相变。畴壁附近的奈尔极化是由弯电效应所引起，畴壁附近的应变梯度导致电荷与电势的再分布，从而产生驱动电场诱导奈尔极化的产生，这是畴壁附近弯电效应的物理本源。另外，通过结合像差校正透射电镜实验和相场模拟，我们不仅观察到了二维全闭合结构，还得到了预测其存在条件的相图。项目执行期间在Nano Letters、Applied Physics Letters、Journal of Applied Physics等国际知名学术期刊上发表十余篇学术论文。