An international research group has produced a previously unknown material: rhenium nitride pernitride. Thanks to combining properties that were previously considered incompatible, it looks set to become highly attractive for technological applications.
The structure of rhenium nitride pernitride, containing single nitrogen atoms (red) and N-N nitrogen dumbbells (blue). The larger balls show rhenium atoms.
Maxim Bykov
The possibility of finding a compound that was metallically conductive, super-hard, and ultra-incompressible was long considered unlikely in science. It was believed that these properties could not occur simultaneously in the same material and were therefore incompatible. But this prejudice has been soundly refuted by the research work now published, which has passed through two stages of development in Hamburg and Bayreuth.
Initially, the scientists synthesised the rhenium nitride pernitride in high-pressure experiments in a laboratory at the University of Bayreuth, and subsequently characterised it chemically and structurally at the German Electron Synchrotron (DESY). "The crystal structure that we discovered in Hamburg at the X-ray light source PETRA III surprised us very much: it contains both single nitrogen atoms and the N-N nitrogen dumbbells, in which two nitrogen atoms are strongly bound to each other. This internal structure obviously creates a very high resistance to pressure acting on the crystals from the outside: rhenium nitride pernitride is ultra-incompressible," says Dr. Maxim Bykov, postdoctoral researcher at the Bavarian Research Institute of Experimental Geochemistry and Geophysics (BGI) at the University of Bayreuth.
New process for synthesising nitrides
At BGI it was subsequently possible to produce the new material in a large-volume press at a significantly lower pressure (33 gigapascals). A reaction of rhenium with ammonium azide is at the heart of the new process. The rhenium nitride pernitride synthesised in this way can be investigated under ambient conditions. The process can be used for the synthesis of other nitrides, in particular nitrides of transition metals, which could also have technologically important properties. This research therefore shows in exemplary fashion the kind of innovation that can come out of high-pressure research in materials science. "Although the exact scope of application for the new material is still hard to grasp, its exceptional combination of physical properties makes rhenium nitride pernitride a material that can help meet the technological challenges of the future," explains Prof. Dr. Natalia Dubrovinskaia of the Laboratory of Crystallography at the University of Bayreuth.