High-(p,T) syntheses and characterisation of binary transition metal carbides and nitrides of the period 6 elements with atomic numbers 73-79

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Carbides and nitrides of heavy transition metals are possible candidates as ultrahard and ultrastiff materials with ultrahigh melting temperatures. It is proposed here to study the formation of novel transition metal carbides and nitrides of the period 6 elements with atomic numbers from 73 to 79 by reaction of the elements at high pressures and high temperatures. First focus will be on the formation of tantalum and rhenium nitrides, and osmium and iridium carbides. Subsequent studies will concentrate on the formation of gold carbide and nitride. Our previous studies have already indicated the existence of a novel high-(p,T) tantalum nitride. The crystal structure of a poorly characterised osmium carbide is discussed controversially. The existence of the other carbides and nitrides has not even been investigated up to now. The final aim is the understanding of the crystal chemistry and structure-property relations in this interesting class of compounds. The formation and stability fields will be determined in the laser-heated diamond anvil cell. Phases will be characterised by powder X-ray diffraction, quantum-mechanical calculations, and Raman spectroscopy. Recrystallisation experiments are aimed at the production of microcrystals for structure determination by micro X-ray diffraction. Larger quantities of sample material will be produced by multi anvil press syntheses for powder neutron diffraction, chemical analyses, and measurements of the physical properties of the reaction products.