Project title: Multiscale theory and simulation of barium titanate      

Supervisors: Dr Paul Tangney, Dr Arash Mostofi and Prof David McComb                                                        

Project decription:

Ferroelectric materials have diverse applications, from fast random access memory to tunable microwave devices, electrocaloric refrigeration, thermoelectric power generation and gate oxides in transistors. The drive toward miniaturisation of ferroelectric materials raises intriguing questions regarding the nanoscopic nature of the ferroelectric effect as the ferroelectric domain size becomes only a few unit cells in extent. On the mesoscopic scale, the pattern of ferroelectric domains exhibits a non-trivial dependence on sample shape and size[1]. This project aims to develop a coarse-grained model to describe the static and dynamic properties of nanoscopic domains at the mesoscopic scale. The theory will be built up from the ab initio level with electronic structure calculations based on density-functional theory on interfaces between ferroelectric domains. This information will be coupled to semi-empirical atomistic potentials that will be used to perform molecular dynamics simulations and to probe the dielectric response to electric fields on length scales of 10s of nanometers. These atomistic models will inform the development of mesoscopic Ginzburg-Landau-like models that will be used to understand the dynamics of domains as a function of sample size and shape. It is hoped that this theoretical effort will be supported by an experimental programme of research, including in situ electron microscopy of domain dynamics. 

[1] A. Schilling, D. Byrne, G. Catalan, et al. “Domains in Ferroelectric Nanodots”, Nano Lett. 9, 3359 (2009).

Research highlights:

  • Talk at NPL: “Ferroelectric domain patterns in nanostructures imaged by HAADF STEM” (December 2010)
  • Co-organiser of: Hermes 2012, an international summer school for multiscale materials simulation and science coommunication (2011-2012)
  • Talk at CMTH Informal Seminar: “Barium Titanate: Phase transitions and density-functional theory” (May 2011)
  • Poster at CECAM workshop: “Density-functional theory  and transmission electron microscopy” (July 2011)
  • Talk at CDT cohort one mini-conference (September 2011)

Outreach activities:

So far my outreach activities have been themed around the importance of structure, in particular the way in which the properties of both novel materials and everyday items can be understood via their atomic and macroscopic structure. An excellent demonstration of the importance of atomic-scale structure can be done with shape memory alloys (SMAs). At room temperature a typical SMA can be freely bent, but it then returns to its original shape upon heating. The phase transition involved in this process has analogies to my primary research area of ferroelectrics. On the macro-scale resonance is an important effect, with a Chinese singing bowl being a practical demonstration that can be done in front of an audience. This is a seemingly everyday bowl of water which forms water spouts when the handles are rubbed. I have recently performed such demonstrations at the The Big Bang: UK Young Scientists & Engineers Fair  and I have been preparing presentations and workshops for school children who will be visiting Imperial.