Material that survived: the “impossible” structure that withstands terrestrial conditions was first obtained
“Materials obtained at pressures of hundreds of thousands of terrestrial atmospheres” sounds proudly, but raises logical questions: “What will happen if the pressure is reduced? What is the point of working with structures that are unable to exist outside of ultrahigh pressures? ” But the point is that once after a long and systematic work you will unclench the diamond anvil, and it turns out that your new material is intact, unharmed, and not going to disintegrate. And then, having a little more “conjured” with complex chemical reactions, you will learn how to obtain it in simpler conditions. It was such a success that the scientists of NUST “MISiS” and their colleagues from Germany and Sweden expected when they decided to modify rhenium with the help of nitrogen. An article with experimental results and their theoretical justification is presented in Nature Communications .
Discussion of the results of theoretical modeling of the atomic structure of a material
Technological progress is merciless: materials used everywhere today will become obsolete tomorrow. Where to go next if everything possible has already been done? That's right - to create the impossible. This is exactly what the international team of scientists from NUST “MISiS”, the University of Bayreuth (Germany) and Linkoping University (Sweden) did - several scientists are already working on the issue of creating superhard modifications of transition metal carbides and nitrides at pressures hundreds of thousands of times higher than atmospheric.
Such metals have high hardness and a high melting point, due to which they are used to create heat-resistant alloys, cutting tools, high temperature sensors, as acid and alkali-resistant protective coatings. The creation of more advanced superhard modifications will bring the use of such materials to a fundamentally new level. But, as they say, "there is a nuance." Earlier experiments proved the possibility of creating “impossible” modifications of nitrides of transition metals for terrestrial conditions, but they “disintegrated” as soon as the pressure decreased. This happened with beryllium oxide , silica , a number of nitrides and hematite .
However, a breakthrough awaited scientists in their latest experience: for the first time, material modified at this pressure retained its new structure and properties under "room" conditions. The material that survived was rhenium pernitride with two additional nitrogen atoms - Re2 (N2) (N2) .
In terms of complexity, this development can be compared to a game of golf, where the hole for the ball is on a steep slope, and you need to find ways to not only throw the ball there, but also to hold it.
In the experimental part of the study, rhenium was placed in a diamond anvil and nitrogen was supplied. Then the anvil was compressed simultaneously with laser heating above 2000 Kelvin (> 1700 ° C). As a result, at pressures of 40 to 90 GPa (400 to 900 thousand terrestrial atmospheres), a special single-crystal structure was obtained - rhenium pernitride and two nitrogen atoms.
“Rhenium itself is practically incompressible, its bulk modulus of elasticity is approximately 400 GPa. But after the modification, it increased to 428 GPa. For comparison, in diamond it is 441 GPa. In addition, due to nitrogen inclusions, the hardness of rhenium pernitride increased by 4 times - up to 37 GPa. Usually, materials modified at ultrahigh pressures are not able to retain their properties after extraction from the diamond anvil, but in this case, fellow experimenters expected success. Of course, this result requires justification, so we started modeling the process on our supercomputer. The theoretical results coincided with the experimental data and made it possible to explain both the unusual properties of the new material and the possibility of its synthesis not only in extreme but also in terrestrial conditions , ”says Professor Igor Abrikosov, Ph.D., scientific adviser laboratory "Modeling and development of new materials" NUST "MISiS", head of the Department of Theoretical Physics, Institute of Physics, Chemistry and Biology, Linkoping University.
Additional nitrogen inclusions - those that increased the hardness of the material 4 times
But here it is important to understand that a diamond anvil is suitable exclusively for experiments - it is too small, complex and expensive to install on a production scale. That is why the next step of scientists was the creation of technology for the synthesis of a new modification of the material in more "simple" conditions. Having received an idea of the processes occurring in the material at ultrahigh pressures, scientists were able to calculate and conduct a chemical reaction with ammonium azide in the press at a pressure of 33 GPa. Now that the existence of such a modification of the material has been proved theoretically and experimentally, other methods for its preparation can be tried, for example, by deposition of thin films.
Discussion of the results of theoretical modeling of the atomic structure of a material
Technological progress is merciless: materials used everywhere today will become obsolete tomorrow. Where to go next if everything possible has already been done? That's right - to create the impossible. This is exactly what the international team of scientists from NUST “MISiS”, the University of Bayreuth (Germany) and Linkoping University (Sweden) did - several scientists are already working on the issue of creating superhard modifications of transition metal carbides and nitrides at pressures hundreds of thousands of times higher than atmospheric.
Such metals have high hardness and a high melting point, due to which they are used to create heat-resistant alloys, cutting tools, high temperature sensors, as acid and alkali-resistant protective coatings. The creation of more advanced superhard modifications will bring the use of such materials to a fundamentally new level. But, as they say, "there is a nuance." Earlier experiments proved the possibility of creating “impossible” modifications of nitrides of transition metals for terrestrial conditions, but they “disintegrated” as soon as the pressure decreased. This happened with beryllium oxide , silica , a number of nitrides and hematite .
However, a breakthrough awaited scientists in their latest experience: for the first time, material modified at this pressure retained its new structure and properties under "room" conditions. The material that survived was rhenium pernitride with two additional nitrogen atoms - Re2 (N2) (N2) .
In terms of complexity, this development can be compared to a game of golf, where the hole for the ball is on a steep slope, and you need to find ways to not only throw the ball there, but also to hold it.
In the experimental part of the study, rhenium was placed in a diamond anvil and nitrogen was supplied. Then the anvil was compressed simultaneously with laser heating above 2000 Kelvin (> 1700 ° C). As a result, at pressures of 40 to 90 GPa (400 to 900 thousand terrestrial atmospheres), a special single-crystal structure was obtained - rhenium pernitride and two nitrogen atoms.
“Rhenium itself is practically incompressible, its bulk modulus of elasticity is approximately 400 GPa. But after the modification, it increased to 428 GPa. For comparison, in diamond it is 441 GPa. In addition, due to nitrogen inclusions, the hardness of rhenium pernitride increased by 4 times - up to 37 GPa. Usually, materials modified at ultrahigh pressures are not able to retain their properties after extraction from the diamond anvil, but in this case, fellow experimenters expected success. Of course, this result requires justification, so we started modeling the process on our supercomputer. The theoretical results coincided with the experimental data and made it possible to explain both the unusual properties of the new material and the possibility of its synthesis not only in extreme but also in terrestrial conditions , ”says Professor Igor Abrikosov, Ph.D., scientific adviser laboratory "Modeling and development of new materials" NUST "MISiS", head of the Department of Theoretical Physics, Institute of Physics, Chemistry and Biology, Linkoping University.
Additional nitrogen inclusions - those that increased the hardness of the material 4 times
But here it is important to understand that a diamond anvil is suitable exclusively for experiments - it is too small, complex and expensive to install on a production scale. That is why the next step of scientists was the creation of technology for the synthesis of a new modification of the material in more "simple" conditions. Having received an idea of the processes occurring in the material at ultrahigh pressures, scientists were able to calculate and conduct a chemical reaction with ammonium azide in the press at a pressure of 33 GPa. Now that the existence of such a modification of the material has been proved theoretically and experimentally, other methods for its preparation can be tried, for example, by deposition of thin films.
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