Tobie Bird

I was a PhD student from the Molecular Analytical Science CDT at the University of Warwick. I was co-supervised by Dr Nicholas Bristowe of the University of Durham. My project involved developing an unbiased method to evaluate the deviation of a local structure from the average, in terms of symmetry-adapted displacements. Local structural information was studied using pair distribution functions (PDFs) of the material in question, obtained via total scattering experiments. This symmetry adapted PDF analysis (SAPA) method is detailed in a recent publication in the Journal of Applied Crystallography. I applied this method to two areas. The first of these is the field of negative thermal expansion, where I analysed the materials ScF3, CaZrF6 and ReO3. The results of the SAPA method helped establish the importance of structural flexibility in determining the magnitude and temperature range of negative thermal expansion in these systems. I also applied the SAPA method to the hybrid perovskite photovoltaic materials CH3NH3PbX3 (X = I, Br, Cl). The SAPA method found high-amplitude "scissoring" modes of the halide anions in these materials. Using density functional theory, we linked these modes to a widening of the electronic band gap. Links to these papers can be found in the publications section of our website.