Shear Phase Inspired OxyFluorides (SPInOF)

Electronically conductive metal oxides represent an extremely important class of materials which underpin technologies from smartphones to efficient catalysts. Surprisingly, they are also rare. Discovering better conductive ceramics could accelerate breakthrough technologies such as spintronic devices for more efficient data storage. Despite their increasing importance, however, there is currently no systematic way to develop new metallic ceramics. The first aim of this project is therefore to create a family of new conductive materials by substituting oxygen for fluorine; namely metal oxyfluorides. Oxyfluorides offer the ability to directly tune the electronic properties of materials whilst preserving the same atomic structure. Specifically, this project will focus on substoichiometric “Magneli” phases where the atomic structure results in high electronic conductivity. These materials also undergo metal-to-insulator transitions as temperature is varied; such behaviour could be used in thermally activated devices (e.g. smart windows) but are also of fundamental scientific interest due to how they arise. Magneli-type oxides are a small but interesting class of materials, therefore Magneli oxyfluorides present an exciting family of materials waiting to be discovered.
Metal oxyfluorides offer chemical flexibility which could be harnessed in many other areas of materials chemistry such as magnetic materials or thermoelectrics, but their uptake has been hampered by difficulties in fully characterising their atomic structure (which underpins the observed properties). Despite these challenges, however, oxygen and fluorine have a strong tendency to adopt well-defined (cis- or fac-type) ordering around metal ions, offering additional influence over physical properties through the presence of “correlated disorder”. The second aim of this project is therefore to accurately determine the oxygen and fluorine arrangement in these new materials using detailed X-ray total scattering techniques and to understand how this structure influences the measured electronic properties. This analysis will also help to understand how the crystallographic structure (particularly crystallographic shear planes) interacts with local bonding of oxide and fluoride anions to promote (or disrupt) anion ordering. This knowledge could then be applied to discover other mixed-anion materials.
Extending this further, the final aim of the project is to actively control the anion arrangement itself during synthesis using the influence of the underlying atomic structure and precise synthetic control. Such ”crystallographic engineering” has not been attempted before, and if successful could allow a much wider range of anion-ordered materials to be synthesised. This is of fundamental interest, but could also offer a new way to control the physical properties of materials by directly tweaking structure at an atomic level.
The impacts of this project will be threefold; firstly, a large number of new metallic ceramic materials will be discovered which could be applied in existing applications (e.g. battery electrodes, catalysts), or advance new technologies (spintronics). Secondly, the link between anion order and physical properties will be better understood, enabling the design of better materials. Finally, methods to directly control oxide-fluoride ordering would offer powerful control of atomic ordering, and could be applied in the future to the discovery of new materials unachievable using existing chemistry techniques.