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In the periodic table of the elements there is a golden rule for the carbon, oxygen and other light elements: under high pressures, have similar structures to the heavier elements in the same group of elements. Less nitrogen, which seemed to be following his own path. Now, researchers of high-pressure chemistry of the University of Bayreuth have refuted this special status. From nitrogen, created a crystalline structure that, in normal conditions, is transformed into phosphorus and black arsenic. The structure contains atomic layers to two-dimensional as those of graphene, is of great interest to the high-tech electronics. Scientists have presented this “ nitrogen black “in the magazine ” Physical Review Letters”.

When you sort the chemical elements in ascending order according to their number of protons and observe their properties, it soon becomes apparent that certain features are repeated at long intervals (periods). The periodic table focuses these repetitions: the elements with similar properties are placed one under the other in the same column and, therefore, form a group of elements. In the upper part of a column is the element that has the least amount of protons and the lower weight in comparison with the other members of the group.

however, the nitrogen is considered the “ black sheep ” of your group. The reason: in previous experiments of high pressure, the nitrogen did not show structures similar to those displayed under normal conditions for heavier elements of this group, specifically, phosphorus, arsenic and antimony . However, such similarities are observed at high pressures in the neighbouring groups, led by carbon and oxygen.

Section of the periodic table: nitrogen (red) and the heavier elements phosphorus, arsenic, antimony and bismuth (green) belong to the group of elements 15. Under extremely high pressures, the nitrogen, as these other members of the group, has a structure that consists of zigzag-shaped two-dimensional layers. Left and right are the groups 14 and 16, led by carbon and oxygen – Dominique Laniel

Researchers from the Institute of Bavarian Research in Geochemistry and Geophysics Experimental (BGI) and the Laboratory of Crystallography, University of Bayreuth, under the leadership of Dominique Laniel, have made a discovery that unusual: pressures and very high temperatures, the nitrogen atoms form a crystal structure characteristic of the phosphorus black , that is a particular variant of the phosphorus. The structure also occurs in arsenic and antimony.

This material is composed of two-dimensional layers in which the nitrogen atoms are cross-linked in a zigzag pattern uniform. In terms of conductive properties, these layers 2-D are similar to the graphene , which shows him as a great promise of material for high-tech applications. The same thing happens with the phosphorous black, which is currently studying its potential as a material for transistors , semiconductors and other electronics .

As the phosphorus-white, the researchers from Bayreuth have proposed a name similar discovered: nitrogen black . Although some features are more potent than phosphorus in the black, the nitrogen black can exist only in exceptional conditions of temperature and pressure under which occurs in the laboratory. In normal conditions, dissolves immediately .

“Due to this instability, the industrial applications are currently not feasible. However, the nitrogen continues to be a very interesting element in the research of materials. Our study shows for example that the high pressures and temperatures can produce structures and properties of materials that the researchers did not know previously existed,” says Laniel.

extreme Conditions for its creation

It took conditions really extreme to produce nitrogen black. The compression pressure was 1.4 million times the pressure of Earth’s atmosphere , and the temperature exceeded 4,000 degrees Celsius. To discover how you arrange the atoms in these conditions, the scientists of Bayreuth cooperated with the Synchrotron-Mail German (DESY) in Hamburg, and the Advanced Photon Source (APS) at Argonne National Laboratory in the united States. Here, X-rays generated by the acceleration of particles have been fired to the samples compressed.

“We were surprised and intrigued by the data of measurement, which suddenly provided us with a structure characteristic of the phosphorus black. Since then, further experiments and calculations have confirmed this finding. This means that there is no doubt about it: the nitrogen, in fact, is not an exception item, but follows the same rule of thumb of the periodic table that carbon and oxygen,” says Laniel.