After graduating from Durham University in 2008 with a 1st class MSci degree in Physics, Nick moved to the University of Cambridge to undertake a PhD in the first principles study of oxide interfaces. He obtained his doctorate in 2012 and moved as a postdoc to Philippe Ghosez’s group, primarily working on novel ways to produce multiferroic (ferroelectric and (anti)ferromagnetic) materials. In 2014 he was awarded a research fellowship from the Royal Commission for the Exhibition of 1851 at Imperial College London, and subsequently an Imperial College Research Fellowship in 2015. His group at Imperial College is investigating how the intricate structure of ferroic (ferroelastic) perovskites can influence physical properties (e.g. thermal expansion and photovoltaic). Since 2017 Nick moved to the University of Kent for a Lectureship in the functional materials group, and remains an honorary lecturer at Imperial.
Room 226, Ingram Building
Also view these in the Kent Academic Repository
Perovskites and related frameworks are often used a prototypical example of functional materials since small changes in chemistry, atomic structure, strain or applied fields can tune or switch the physical behaviour of the material in a way which could be useful for various types of devices. Some of these materials are also natural minerals and important in the field of Earth Sciences.
Symmetry lowering phase transitions, appearing even from just small atomic distortions, can have a large influence on physical properties. Common examples include metal-insulator transitions due to breathing distortions, orbital and magnetic ordering from Jahn-Teller distortions and paraelectric to ferroelectric transitions from polar off-centrings. Our group recently showed that the thermo-mechanical properties of layered perovskites can be changed drastically (e.g. from thermal expansion to contraction) by just small octahedral tilting in the crystal structure.
Figure 1: The atomic positions forming the crystal lattice are strongly coupled to the electronic degrees of freedom (spin, charge and orbital) in perovskites.
Emergent phenomena at interfaces
Interfaces between two materials, or within a single material (e.g. surfaces, twinning), can drastically influence the physical properties of the system. Interfaces can do this via, for example, the symmetry lowering, electrostatic coupling and chemical bonding that occurs at the boundary. Perhaps the prototypical example over the last decade has been the interface between the two perovskites, LaAlO3 and SrTiO3, which can become electrically conducting, even though the two are insulating in the bulk. Other areas of interest are emergent ferroic (e.g. ferromagnetic / ferroelectric), or electronic, behaviour at twin walls or surfaces.
Figure 2: Spin canting at the surface of the ferromagnetic (La,Sr)MnO3
First principles methods
Often it is highly desirable to turn to a theoretical tool which does not rely on experimental parameterisation. For example, when designing new materials which have yet to be made, when exploring phase space of a material which has yet to be studied, or when attempting to unravel the underlying mechanisms behind unexpected observations. Density functional theory (DFT) is now a computationally affordable method to study the ground state of even fairly complex materials at the microscale. When properties associated with processes occurring at the mesoscale are required (e.g. dynamical properties or domain wall evolution), DFT can be used to parameterise classical atomic potentials.