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

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.

Impact on the experimental research Nano-scale and nano-structured materials are now central to innovative research strategies in healthcare, electronics, materials for energy applications and other areas. Our work on the fundamentals of nano-scale ferroelectrics and the mechanisms of controlling their properties will have direct impact on the strategies for control at the nano-scale. JC has a proven record of conveying important research results across different disciplines and facilitating multi-disciplinary collaborations. PVS collaborates with experimental groups in Europe, USA, and Japan working on other types of nano-structures. These multi-disciplinary links will make it straightforward to promote the knowledge transfer between different communities. Economical and environmental impact Control over properties of individual nano-structures paves the way to innovative device engineering. Novel devices based on the use of nano-scale ferroelectric materials are promising to, for example, significantly impact data storage technologies with fast terabit-per-square-inch memory devices. Other important applications include cheap room-temperature magnetic-field detectors, microfluidic systems, and electrocaloric coolers. Once these devices become readiy available, the society, as a whole, will benefit through the use of the technological advances and new business opportunities, and, importantly, through reduced energy consumption requirements for operating advanced devices. Impact on the materials modelling Our work will enhance computational capabilities and facilitate accurate modeling of realistic nano-structures. Material modelling community will benefit from using the multi-scale computational methodology either directly, i.e. as implemented in our computer codes, or indirectly, i.e. by applying similar strategy to other systems. The range of potential applications of multi-scale computational methods goes well beyond condensed matter physics and includes chemistry and biochemistry, materials, devices, astrophysics, and other disciplines. Importantly, these theoretical studies can provide insight into materials properties at a scale inaccessible to most experimental techniques and, thus, guide and stimulate further fundamental and applied experimental studies. To make our results available to beneficiaries we will 1) Distribute them through usual academic routes including publications in scientific journals, online publications, conference presentations and discussion meetings. 2) We will establish collaborations with experimental community via the appointed PDRP who will be working in close cooperation with experimentalists at NPL and their partners in industry. 3) We will prepare comprehensive documentation for all computational tools, which we will develop and make the computer codes and our expertise available to the wider modeling community.