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

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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.