New Materials from High Pressure and Beyond

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The discovery of new materials for electronic, magnetic and energy techmology applications motivates much of modern chemistry, physics and materials science. High pressure methods are important for materials synthesis and for inducing new electronic states. This project will explore exciting new materials and also new ideas for materials discovery that go beyond standard high pressure synthesis approaches. In our high pressure materials syntheses, a chemical reaction is carried out at pressures up to 150,000 atmospheres pressure and temperatures up to 1500C. Afterwards the sample is cooled and then decompressed to ambient conditions. In successful cases, a novel material with a new chemical composition or structure is found to have been 'recovered' from the high pressure and temperature reaction conditions. This is a successful discovery strategy for dense, oxide-based, inorganic materials and will be applied to several specific cases. Magnetite is the original magnetic material and remains of fundamental interest and of practical importance in new technologies such as spintronic devices. We have recently solved a long-running problem (first identified in 1939) concerning the low temperature electronic structure of magnetite and we discovered unexpected 'orbital molecule' states where electrons are spread over three adjacent iron atoms. In this project we will use high pressure synthesis to recover new chemically-substituted analogues that preserve the essential electronic features of magnetite, in order to discover new 'orbital molecule' states or arrangements. Ruthenium also forms important magnetic oxides such strontium ruthenate which is used in spintronic and silicon thin-film electronics devices. We have recently discovered a new familty of ruthenium oxides, and high pressure will be used to explore their chemical composition range and electronic and magnetic properties.Oxynitride (oxide-nitride) materials are important for energy technologies as photocatalyts that split water to generate hydrogen, and as phosphors for WLED white-light emitting semiconductor devices. WLED devices are an excellent example of how device innovation (discovery of GaN-based blue LEDs) and materials chemistry (discovery of nitride phosphors) have led to real energy savings on a global scale. We will use a direct high pressure synthesis route to generate new oxynitrides and explore their propeties through collaboration.The successful preparation of a material is usually the chemical end point for high pressure synthesis, but we will also explore new approaches where a synthesised high pressure material is the starting point for chemical investigations. This can be described as a 'hard-soft' method to generate novel materials by relieving the instability of a dense precursor made under 'hard' high pressure and temperature conditions through 'soft' post-synthesis modification. Recent proof-of-concept results have shown that 'hard-soft' chemistry can generate new transition metal oxides beyond high pressure synthesis. We will also perform high pressure measurements of electronic and magnetic properties of recovered materials to discover electronic properties beyond those at ambient pressure, including very low temperature regimes where quantum mechanical variations are important.