MOSCOW, July 9, 2019 /PRNewswire/ -- NUST MISIS scientists together with colleagues (Germany, Sweden and Russia) proved the possibility of creating materials, which were considered unreal in terms of the classical understanding of chemical laws. By subjecting beryllium oxide to pressure hundreds of thousands of times higher than atmospheric one, the researchers achieved a transition of the crystal structure with beryllium coordinated with five and six oxygen atoms, although it was previously thought that the maximum possible number could be only four. The results of the experiment and their theoretical explanation are presented in Nature Communications.

Imagine that you have a plethora of cubes, and you are going to build something out of them, – the authors of the study describe their work. – You can build a lot of different things, but still their number is limited by the form of "building materials", because they can only connect with each other in a certain way. And now imagine that you have the opportunity to change the shape of these cubes – stretch them, add faces, i.e., modify so that the number of possible combinations of the resulting "building materials" increases countless times.

Actually, the building blocks of the crystal structure of materials can be viewed as these "cubes". If we modify these building blocks, we can give the materials fundamentally new properties. However, not all transformations are possible, traditional understanding of chemical laws proclaims.

The search for the solution of this problem – overcoming "impossibility" – is a joint project of NUST MISIS scientists and their colleagues from University of Bayreuth (Germany) , Linköping University (Sweden) and Institute of Earth Sciences and Kola Science Center (Russian Academy of Sciences).

The results of their research – laboratory experiment and its theoretical modeling – demonstrated that obtaining "impossible" modifications of materials is actually quite possible. It is necessary to subject them to ultrahigh pressures, hundreds of thousands of times higher than atmospheric.

"We worked with hurlbutite, which is beryllium compound, CaBe2P2O8. In standard conditions, beryllium forms tetrahedral pyramids with oxygen atoms, and until recently it was believed that this is the maximum possible coordination of beryllium. However, our colleagues from Germany conducted an experiment, which revealed that the crystal structure can be reconstructed. During the experiment, the material was placed in a diamond anvil cell, where it was exposed to ultrahigh pressures. Thus, at a pressure of 17 GPA (170 thousand Earth's atmospheres) there was an increase in the number of oxygen atoms surrounding berylluim to five, and at a pressure of 80 GPA (800 thousand Earth's atmospheres), the crystal was reconstructed so that this number increased to six. This is an incredible result that no one has ever presented before. That is why a theoretical proof was needed, and the study of which we are engaged independently on our supercomputer," said professor Igor Abrikosov, scientific advisor of NUST MISIS Materials Modelling and Development Laboratory, Head of Theoretical Physics Division at the Department of Physics, Chemistry and Biology, Linköping University, explains.

Theoretical modeling of the results of the experiment was carried out by NUST MISIS scientists just in a month. To solve the Dirac equation with the given variables, all the computing power of the supercomputer cluster of Materials Modelling and Development Laboratory was used. Without the supercomputer it would never have been possible to carry out calculations of such complexity, as the usual computers simply would not have enough power. The results of the calculations almost completely coincide with the results of the experiment, the differences are minimal, and are within the margin of error.

As Professor Abrikosov notes, in many respects beryllium was chosen as an experimental material because it is highly demanded in engineering and space industries. Nevertheless, the research is fundamental: studying the modifications of specific materials, it is possible to build a General theoretical model that would allow systematizing the processes and conditions necessary to create "unreal materials". In the nearest future scientists plan to continue research, in particular, with polynitrides. 

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SOURCE The National University of Science and Technology MISiS