EFFECT OF UNIAXIAL STRAIN ON BULK BISMUTH FERRITE
This project is a joint venture of Prof. Maximilien Cazayous at the University of Paris and the group of Prof. Laurent Bellaiche at UARK, US. Our aim is to predict the ground state configuration of bulk Bismuth Ferrite under uni-axial strain along specific psuedo cubic directions. These predictions will then aid Prof. Cazayous in their experimental work.
VORTICES IN BFO/STO SUPERLATTICES
BFO: Bismuth Ferrite is a room temperature multiferroic ie., it shows both ferroelectric and ferromagentic properties at room temperature. Now imagine Bismuth Ferrite film on a substrate. In this project, I am computationally studying the effect of different substrates, and hence different substrate strains on the magentic and polar structure of the birmuth ferrite film,with special focus on the possibility of vortices.This project is a joint venture of Prof. Nagarajan Valanoor at UNSW Sydney and Prof. Laurent Bellaiche at UARK, US. Once the effect of single substrate on single film is established, we want to study the effect of superlattice (thickness and strain of respective layers) on both BFO and STO parts of the superlattice.
CHARACTERIZATION OF RELAXOR FERROELETCRIC SINGLE CRYSTALS
Relaxor ferroelectrics have the characteristic property of relaxed dielectric dispersion. In addition its maximum dielectric permittivity and the temperature at which the maximum happens changes as a function of the frequency. These materials are argued not to have a conventional domain structure like other ferroelectrics, sometimes explained as having polar nano regions while other theories explain using exceptionally large number of domain walls. Either way, this response can be studied using diffuse scattering. Diffuse scattering is diffuse intensity around actual Bragg peaks. The shapes of the diffuse scattering intensity and the changes in those shapes with external stimuli have been related to the domain structure of relaxors for e.g., the shape of the polar nano regions. In this project, we are trying to study the diffuse scattering of PMN-PT single crystals while varying the electric field and stress to understand how this stimulus affects the shape of the diffuse intensity and therefore the domain structure in relaxors.
FERROIC DOMAIN PERCOLATION
This project is about investigating the probability with which ferroic domains can continue across a microstructure. Why one could ask. Well, since the 1950s, polycrystals with continuous domains have been observed experimentally. But not much research was done to check when is it likely and what do materials scientists need to ensure in order to make this possible. This was my Ph.D. project, although I am still working on it. I started with formulating the conditions that were needed to be satisfied in order for ferroic domains to continue over grain boundaries. Once I had the conditions, I applied them over 5 dimensions of the grain boundary. Yep, 5 dimensions! Actually, if you think about it, not that hard to understand. If you are interested in knowing more about this, message me or my Ph.D. supervisor (Dr. John Daniels http://www.materials.unsw.edu.au/profile/john-daniels). If you are thinking of doing a Ph.D. and for some reason you imagine your supervisor to be an easy-going Aussie dude who does not make you work on weekends, he is a great guy to work with!
PREDICTING PERMISSIBLE DOMAIN WALLS IN FERROICS
Now you would think, isn’t that established knowledge. You are right, it is. We already know the permissible domain walls in tetragonal, rhombohedral and orthorhombic systems (at least most of them, some of them vary with temperature). So I went to my Ph.D. supervisor (yep, same Aussie dude) asking why? He looked at me and said, “you know what, figure it out.” So instead of going into literature (the sane thing to do), I started my journey of predicting something already present in literature. But the feeling of calculating something already well known and getting to the answer is divine. The interesting part is that now we are using this to predict the walls in symmetries where prior knowledge does not exist yet or predicting the change in the domain walls due to external stimuli like the electric field, mechanical force, or temperature.