Learning to control structure and properties of nano-scale ferroelectrics using defects

铁电材料由于其在例如存储器装置、电容器和传感器中的应用而长期受到广泛的技术关注。成功地改善现有设备的功能和开发新的质量依赖于更好地控制材料性能，并最终根据需求定制它们的能力。该方案的主要目的是研究原子尺度的化学键合特征、~5 nm尺度的铁电畴的结构和性质以及~10-100 nm尺度的纳米尺度铁电样品的整体尺寸和形状之间的相互作用。这些知识将提供巨大的机会，在控制纳米尺度的铁电体的性质，通过改变其化学成分，施加一个外部场，暴露于紫外光，塑造其结构和应用capping layers.We将开发一种新的方法相结合的从头算原子模拟纳米尺度的铁电体和实用程序的域结构的有效分析。这些方法将被应用到获得的统计分布的领域在纳米尺度BaTiO 3和分析之间的相关性的域属性的分布和尺寸和形状的BaTiO 3纳米结构。在长度尺度的另一侧，我们将研究由氧空位的形成引起的畴结构的修改。我们将研究浓度依赖性的缺陷引起的性能，并考虑到氧空位可以存在于几个电荷状态。最后，我们将考虑含缺陷的样品与外部电场的相互作用，并研究在有限温度下的域的动力学。这些研究的结果将揭示点缺陷对纳米级铁电体性质的影响，并将提供通过操纵缺陷的电荷状态和通过改变它们的浓度来控制这些性质的机制。这些发现将刺激进一步发展的表面探针方法，特别是在该地区的控制操纵表面原子使用扫描隧道显微镜或原子力显微镜技术。

Ferroelectric materials have long been of widespread technological interest for their applications in, for example, memory devices, capacitors, and sensors. Success in improving the functionality of existing devices and development of qualitatively new ones relies on achieving better control of the materials properties and, ultimately, the ability to tailor them on demand. The main aim of this proposal is to investigate the interplay between the character of the chemical bonding at the atomic scale, the structure and properties of the ferroelectric domains at ~5 nm scale and the overall size and shape of the nano-scale ferroelectric sample at ~10-100 nm scale. This knowledge would provide huge opportunities in controlling the properties of nano-scale ferroelectrics by changing their chemical composition, applying an external field, exposing them to ultra-violet light, shaping their structure and applying capping layers.We will develop a novel methodology for combined ab initio - atomistic modelling of nano-scale ferroelectrics and utilities for efficient analysis of the domain structure. These methods will be applied to obtain a statistical distribution of the domains in nano-scale BaTiO3 and to analyse the correlation between the distribution of the domain properties and the size and shape of the BaTiO3 nano-structures. On the other side of the length-scale, we will investigate the modification of the domain structure induced by the formation of oxygen vacancies. We will investigate the concentration-dependence of the defect-induced properties and take into account that oxygen vacancies can exist in several charge states. Finally, we will consider the interaction of the defect-containing samples with an external electric field and investigate the dynamics of the domains at finite temperatures. The results of these studies will reveal the effects of the point defects on the properties of nano-scale ferroelectrics and will provide mechanisms for controlling these properties by manipulating the charge states of the defects and by changing their concentrations. These findings will stimulate further developments in surface probe methods, particularly in the area of controlled manipulation surface atoms using scanning tunnelling microscopy or atomic force microscopy techniques.