ERA-Chemistry: Searching for ultra-incompressible materials: Formation and characterisation of binary and ternary period 6 transition metal borides at very high pressures and temperatures

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One approach for the directed search for ultra-incompressible compounds is based on the idea that acombination of a high valence electron density in conjunction with covalent bonds should providecompounds with the desired properties. This has led to an extensive search for compounds containingheavy transition metal ions of period 6 (Ta,W,Re,Os,Ir) and a light element, such as carbon, nitrogen orboron. Some of these compounds, such as OsB2, have indeed shown outstanding physical properties, but several compounds, which are thought to be very promising, such as a rhenium boride with a B:Re ratio > 2, have not been synthesized yet. It is well established that high pressure/high temperature conditions may lead to unusual bonding environments and new structure types. However, our knowledge of the high pressure behavior of binary period 6 transition metal borides is rather limited. While the corresponding carbides and nitrides are well investigated, no in-situ synthesis studies of borides at extreme p,T-conditions have been published yet and hence our knowledge of the p,T-phase stabilities of binary and ternary period 6 transition metal borides is extremely limited. Hence, the current proposal focusses on understanding phase-relations, structures and properties of binary and ternary period 6 transition metal borides obtained at very high pressures and temperatures in laser heated diamond anvil cells and large-volume high pressure devices, complemented by mechanochemically activated synthesis with high speed ball milling and density functional theory based atomistic model calculations. Samples will be characterized by numerous techniques, including microcalorimetry, vibrational spectroscopy and neutron diffraction on isotopically enriched compounds. The project fully exploits the complementary expertise and available experimental equipment in Innsbruck and Frankfurt and promises to yield novel compounds, a deeper understanding of the crystal chemistry of borides and possibly a route to synthesize materials with outstanding properties.