Structure and Properties of Transition Metal Oxychalcogenides and Oxypnictides

This project falls within the EPSRC 'Physical Sciences' research area and is also related to the 'Energy' theme. The project will focus on the synthesis and characterisation of certain transition metal oxychalcogenides and oxypnictides. These compounds are mixed-anion materials which tend to form layered structures and exhibit a number of desirable properties. For example, they can be superconductors, semiconductors or ionic conductors. In particular, the magnetic properties of these solids will be probed in order to gain an understanding of any long range magnetic ordering present and to explore the nature of this ordering over a given temperature range. These layered materials also have the potential to be used as cathode materials in Li-ion batteries due to the possibility of Li-Cu exchange and then deintercalation and intercalation of the Li ions. The targets that are successfully made will be tested as battery electrodes if this seems chemically viable, and this clearly aligns with the UK research strategy. This part of the work will be collaborative with the Faraday Institution FutureCat project. The project will involve the production of novel compounds. This can be achieved through the substitution of ions in known structures, such as changing the transition metal present on a crystallographic site, and this has the effect of tuning the electronic and magnetic properties. New materials may also arise when a particular synthetic target is attempted, but a more energetically favoured new product is formed instead; careful examination of structural data will enable this to be ascertained and the new compounds to be synthesised as pure phases, opening up new research avenues. The characterisation of both new and existing materials will be performed in depth. Structure, magnetic order and certain aspects of reactivity will be focussed on specifically. Although predictions about the behaviour of solids can be made computationally, it is only once these materials themselves have been tested that their properties are truly known. The materials are synthesised using the tradition ceramic solid state method of grinding reactants together using a pestle and mortar and then heating the homogeneous mixture to high temperatures in a furnace. Due to the likely oxygen and moisture sensitivity of both reactants and products, this preparation is carried out in an argon-filled dry box with the reactant mixture being sealed under vacuum in a silica tube before being heated in the furnace. Structure determination is achieved through Rietveld refinement of x-ray powder diffraction data collected on x-ray diffractometers in house and at the Diamond Light Source (Harwell). An in house magnetometer is used to measure the magnetisation of samples, generally from room temperature down to 2 K. Neutron scattering carried out at neutron sources, such as the ISIS Facility (Harwell) and the ILL Facility (Grenoble, France), is an essential technique for the exploration of magnetic ordering within these compounds. Crystal growth of selected important materials in Oxford Physics will enable a wider range of physical property and spectroscopic measurements to be performed, and new properties to be realised within the Physical Sciences theme. High pressure synthesis may also be appropriate and this will be carried out in collaboration with Element 6 located at the Harwell campus.