Structure-Reactivity Relationships for Extended Solids: Tailored Design of Highly Functional Materials

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Oxide based materials are very common and have played vital roles in miniaturization of technologies and have opened up avenues for higher efficiency devices. The performance of rechargeable batteries have improved significantly during the last decade and are now reliable components in all types of devices (cell phones, computers, cars, medical devices). Solid Oxide Fuel Cells (SOFC) are highly efficient secondary power sources that can tolerate diverse fuels and require almost no maintenance. At the center of most of these devices are inorganic solid state materials that need to optimized for their respective functions. There is a tremendous need for tailored materials that can provide reliable and efficient performance while being economically competitive. This proposal is concerned with these functional inorganic materials and their controlled preparation and processing. Unfortunately to date the chemical reactivity and formation of solid state materials is only very poorly understood. In fact the successful targeted preparation of a functional material often depends on the experience and intuition of synthetic chemists. Our target compounds are ceramics with applications in energy conversion, oxide ion conductors for solid oxide fuel cell (SOFC) technology and novel layered lithium conductors for rechargeable batteries. Unfortunately almost no rational design strategies for the synthesis of inorganic materials are available. The same materials composition can result in a variety of different structures with different properties, traditionally most metal oxides are prepared directly at high temperatures (T > 1000°C) while ignoring the structural and thus functional diversity accessible at lower temperatures using indirect synthetic routs. The Bieringer research group has clearly demonstrated the large number of metastable structures that are accessible at lower temperatures. We monitor solid state chemical reactions in real time and derive reaction pathways which provide structure-reactivity relationships for extended solids. At lower temperatures we have encountered diverse oxide defect structures (oxide defect structures are responsible for oxide ion conduction) with potential applications as solid state electrolytes. In this particular proposal we aim at further exploring solid state reaction pathways in an attempt to establish reliable structure-reactivity relationships which will enable the rational design of functional solid state materials. The second component of this proposal deals with low temperature topotactic reactions where we only modify parts of a structure during the reaction. We are employing metal hydrides as solid state reductants. Those permit us to prepare metastable products derived from the parent host structures and can exhibit unusual oxidation states and coordination environments. A specific application is concerned with the simultaneous reduction (topotactic oxide ion removal) and cation intercalation in layered oxide structures. These phases are potentially tunable lithium conductors for rechargeable battery technology. The proposed research program will provide unique training opportunities for students and prepares graduates for the renewable energy research environment in Canada.