New transition metal oxychalcogenides

In this proposal we request funding to investigate the synthesis, structures and electronic/magnetic properties of a variety of new transition metal oxychalcogenides. These are relatively unusual materials which simultaneously contain an oxide (O2-) and a second chalcogenide (S2-, Se2-, Te2-) anion, as opposed to more commonly found species such as sulfates or sulfites (SO42- and SO32-) in which the chalcogen has a positive formal charge. Mixed anion materials are interesting as they frequently contain transition metals in unusual chemical or electronic environments. This can lead to materials with unexpected and fascinating electronic, magnetic or optical properties. A now-classic example of this was the 2008 discovery by Hosono et al. of 26 K superconductivity (now known at temperatures up to 55 K) in materials derived from a oxypnictide LaOFeAs. Superconductivity in an iron-based system such as this at such high temperatures was unprecedented, entirely unexpected and led to significant world-wide interest. Other interesting mixed anion phases include materials such as LnOCuS (Ln = lanthanide) and La2O2CdSe2, which are rare examples of p-type transparent conductors, and could find a range of applications in display devices.

In this research programme we plan work in three main areas. Firstly, we want to tune the electronic properties of a fascinating and unusual family of materials of composition Ln2O2M2OSe2 (Ln = lanthanide, M = transition metal). These are closely related to the superconducting pnictide systems but, in their undoped state, lie on the insulator side of a insulator-to-metal boundary. We plan various approaches to chemically modify them to change their conductivity, ideally towards the superconducting region of the phase diagram, and to understand both their structural and physical properties. Secondly, we aim to extend our recent successes in the preparation of novel materials with the closely related composition Ln2O2MSe2. We again aim to understand, control and exploit their electrical and optical properties. We believe discoveries here will also help understand the pnictide systems. In our final work strand we believe that we can adopt a variety of ideas learned from our work and that of others to prepare new families of materials of general formula (LnOQ)1-xMx and (LnOQ)1-xMQx - what we call "4 Angstrom phases". Our aim is to explore the properties of these new phases.

The synthetic side of our work will be supported via a variety of characterisation and theoretical methods. We will apply X-ray and neutron scattering techniques to probe the structures, structural changes and magnetic interactions in the materials. The physical properties of interesting materials (conductivity, magnetism, heat capacity, etc) will be measured using equipment available in Durham. Plane wave density functional theory will be used to help us predict and understand the properties of materials targetted or prepared. We believe this synergic approach will allow rapid and insightful progress.

The work of this proposal is of a fundamental nature. It aims to prepare and understand new oxychalcogenide materials with novel electronic, optical or magnetic properties. The short term impact will therefore be largely on academics in related disciplines (see academic beneficiaries); direct impact on the private sector, policy makers, and the third sector within its three year timeframe is likely to be minimal. That said, the impact of materials-discovery programmes on a longer (10+ year) timescale is potentially enormous. There are numerous examples of inorganic oxide and chalcogenide materials that have reached applications and had huge societal impact that one could cite including: low and high temperature superconductors used in devices as diverse as high field MRI magnets and ultra-sensitive squid sensors; the zeolites used to crack essentially every drop of gasoline; transition metal oxides used as cathode materials in rechargeable batteries; rare earth doped phosphors; oxide ion conductors used in high temperature fuel cells and oxygen sensors; microwave dielectrics used in mobile phone communications; and others. Each of these use inorganic solid state materials which have moved from the laboratory to devices in relatively short time frames, and each has direct and significant daily impact on the general public. The purely financial impact of some of these examples is huge: the multi-billion dollar petroleum industry is entirely reliant on zeolite-based chemical transformations.

As detailed in "Pathways to Impact" our work during this project will also have indirect impact on academics and industry globally who rely on the myriad applications of powder diffraction in areas as diverse as pharmaceutical polymorphs, mining and minerals, process control and even protein structure. We have a history of innovation in powder diffraction methods and a strong track record of rapidly sharing and disseminating our ideas via training schools, on line tutorials and wiki sites. This benefits industry, UK and world academics and also users of major national facilities such as ISIS, Diamond, the ILL and ESRF. We also commonly apply expertise derived during projects such as these to industrial problems. During this specific project we anticipate significant spin-off developments in understanding magnetic structures using Topas-academic (a widely used software package we help develop).

The highest direct impact on the general public during the course of the research will be derived by including specific examples from our work in our Departmental "Amazing Materials" interactive display, which we show regularly during science outreach events with the local community. We find that demonstrating "counter intuitive" materials' properties (many from EPSRC-supported research) is a powerful way to engage children and the general public, and can be used as a starting point for discussing the importance of scientific research to the future UK economy.