High pressure crystal chemistry and compression behaviors of novel early transition-metal nitrides*

Transition-metal (TM) nitrides have attractive physical and chemical properties, such as superconductivity, peculiar magnetism, eminent hardness, distinguished catalytic capability etc. Accordingly, they have been studied from the viewpoints of not only fundamental sciences but also materials science and engineering. Particularly, nitrogen-rich TM nitrides are paid the most attention to now because the laser-heated diamond anvil cell (LH-DAC) is a powerful tool to synthesize novel metal nitrides at ultra-high pressures above dozens GPa ranges. We have reported synthesis, crystal chemistry and electronic structure of various kinds of novel late TM nitrides, such as FeN₂, CoN₂, FeN, CoN, RhN₂, RuN₂, IrN₂, PtN₂ etc. Recently, we have also succeeded in synthesizing novel early TM nitrides using LH-DAC. Especially, single crystals of a novel Cr-nitride have been grown in a supercritical nitrogen fluid and characterized by the synchrotron X-ray diffraction and Raman scattering measurements under both high and ambient pressures. First-principles calculation has been also carried out to evaluate and discuss the electronic structure of these nitrides above. This talk will systematically discuss about novel early TM nitrides as well as late TM ones.