Control of Crystal Chemistry and Crystal Form in Complex Oxides by Mild Synthesis

Our proposal is to investigate new synthetic chemistry for the preparation of complex inorganic materials that introduces various degree of control in the preparation of materials, ultimately for real-life uses. Advanced materials for technological applications require the synthesis of samples with precise control over the chemical composition of the sample (the ratio of various chemical elements in a sample and their chemical state) and also control over the form of the sample (particle size and shape over length scales from nanometres to micrometres). Our hypothesis, based on some preliminary results, is that solvothermal conditions (the combination of a solvent and simple chemical precursors in a sealed reaction vessel heated above the boiling point of the solvent, rather like a household pressure cooker) will permit these levels of control to be achieved in a one-step process. The synthetic method has already been applied for the preparation of porous materials, but we will instead study ceramic-type materials, materials that would usually be prepared using extreme temperature in excess of 1000 oC, with repeated grinding and firing cycles. These materials all have extended network structures (effectively infinite, within the bounds of an individual crystal) and therefore their synthesis and crystal growth must be controlled in one step: unlike solids made up by the packing of molecular units where recrystallisation is easily achieved. With the use of mild conditions and a solvent, we aim to first undertake exploratory synthesis to investigate the possibility of isolating new materials, not seen at high temperature, and then second develop control over the growth of crystals making up the sample, to optimise their properties for practical applications. The novelty of our synthetic approach will include the design and commissioning of a new multi-cell reactor in collaboration with a project partner, Baskerville Ltd for routine operation at up to 500 oC. We believe that we can introduce control of crystal growth at three levels: (1) the control of the metal oxidation state (a measure how the electrons holding together the solid structure are located in relation to the metal atoms) by use of chemical reagents, (2) control of the arrangement of atoms in the extended solid structure by choice of partner metals, which will dictate how atoms pack to form the solid structure, and (3) control over crystal form, the shape and size of individual crystals making up a specimen. Such fine control is rarely achieved in the synthesis of inorganic materials, and our work would therefore provide significant results for the 'design' of new solids. In order to test these ideas we have carefully chosen target materials whose properties are dictated by the chemical environment and oxidation state of constituent atoms: these materials are used in catalysis where the switching of metal oxidation states in the solid-state gives rise to their properties ('redox catalysis'). With industrial project partners, Johnson Matthey plc, preliminary assessment of these properties will be achieved, and by collaboration throughout the project, we will be able to use the results to inform and direct the synthetic chemistry. This will be the first step of putting materials into real life applications: redox catalysts form the base of catalytic converters for the destruction of pollutant molecules, production of fine chemicals, and in the production and purification of hydrogen for future energy sources. Although a fundamental synthetic chemistry programme in materials discovery, our work, will therefore extend into the first steps of investigating the use of the materials we make in real-life applications.