Ordered States in Oxides

The electronic properties of transition metal oxides continue to drive many fields, from fundamental condensed matter physics and solid state chemistry to materials science and engineering applications. High temperature superconductivity (HTSC) in copper oxides and colossal magnetoresistances (CMR) in manganite perovskites are two particularly important phenomena that have led to many other perovskite oxides being widely studied for their electronic properties.Knowledge of structure is always important for understanding materials properties. Transition metal oxide structures are often based on simple high symmetry structures e.g. perovskite, spinel, but the above orderings lower symmetry leading to slight lattice distortions and superstructures. It has become clear that much subtle but important information can be gained from high resolution powder diffraction studies. Powder diffraction is needed partly because many of these materials are difficult to crystallise, but more fundamentally, the distortions lead to severe (micro)twinning in crystals that makes conventional single crystal structure determinations difficult (e.g. in the case of Fe3O4).Powder diffraction is a simple technique but remains one of the most popular in the synchrotron X-ray and neutron user communities. A variety of instruments are now available at ISIS, ILL, ESRF and (in the future) Diamond. These are applied to many problems in chemistry, physics, materials science, engineering and geosciences. To make the best use of available facilities, as well as providing a broad training in leading powder diffraction techniques, this project will study several materials using a range of instruments.The structures and magnetic order in high pressure Cr, Ru and Bi-based perovskites will be investigated. These materials will be synthesised using a recently commissioned Walker press. The complex superstructures associated with charge, spin and orbital order in RBaMn2O6 manganites will also be studied. Charge ordering in magnetite (Fe3O4) is a classic and long running problem. We aim to improve on a previous structural model through further high resolution powder diffraction study, and analysing data from heavily twinned microcrystals. Further aspects of the student training will be through attending workshops in Grenoble (HERCULES) and ISIS, and by 3 month visits to each centre.