Russian Scientists Have Found A Substance As Hard As A Diamond
An algorithm developed by Russian scientists for computer modeling of crystal structures allowed us to predict potential superhard compounds that are comparable in hardness to diamond. The results are published in the journal of Physical Chemistry Letters.
Earlier, Russian physicists led by Professor Skoltech and MIPT Artem Oganov created an evolutionary algorithm for predicting crystal structures USPEX and then based on it proposed a list of solid and superhard materials that have potential applications in many areas of industry. This list is called the "treasure map" for experimenters.
The greatest interest in this "treasure map" are compounds that have a high Vickers hardness — the pressure required to get a pyramid-shaped imprint on the material, combined with the crack resistance-the ability of the material to resist the spread of cracks.
First of all, these are transition metal borides. Their synthesis, unlike the widely used diamond and cubic boron nitride, does not require high pressure, which reduces the cost of production.
High electron density on the outer shell of metal atoms prevents compression, electrons begin to repel each other, and strong covalent bonds of boron-boron and boron-metal provide strength under elastic and plastic deformations.
In previous work, scientists found one previously unknown structure of tungsten boride - wb5 pentaboride and found out that it is super hard. In a new paper, scientists from Skoltech, MIPT, the Prokhorov Institute of General Physics of the Russian Academy of Sciences, the Pirogov Russian national research medical University, and Northwestern Polytechnic University in Xi'an, China, studied the properties of molybdenum borides.
The most energetically advantageous from the point of view of creating such compounds were the higher borides of molybdenum, in which one atom of molybdenum accounts for four to five boron atoms.
The most stable of them is MoB5 molybdenum pentaboride, which has a calculated Vickers hardness of 37-39 gigapascals, which makes it possible to consider it as a potential superhard material that can replace traditionally used hard alloys and superhard materials in a number of technological applications.
The main structural elements of the new compound are graphene-like layers of boron atoms, layers of molybdenum atoms, and triangles of boron atoms. Layers of boron and layers of molybdenum alternate with each other, while some of the molybdenum atoms are seen In 3-triangles evenly distributed over the volume of the crystal.
"We suggested that the structure of the higher boride should have a disordered structure in which the boron triangles will statistically replace the molybdenum atoms. To confirm this, we developed a lattice model to determine the rules by which the triangles of boron must be placed in the crystal to have the least energy," presented in a press release, the words of the first author Dmitry Rubcovskaja, researcher Skoltech and IOF them. A. M. Prokhorov, Russian Academy of Sciences.
A computer search of variants of the arrangement of molybdenum atoms and boron triangles has revealed patterns according to which the most stable compounds are formed, where one metal atom has from four to five boron atoms. The most stable composition was MoB4. 7. This is very close to the theoretical MoB5 compound predicted by the USPEX evolutionary algorithm.
"This work is an interesting example of the interaction of theory and experiment. The theory predicted a compound with interesting properties and a new structure, but the experiment showed that the real substance is more complex and has a partially disordered structure, " says Artem Oganov, the head of the study.
Superhard materials have a wide range of applications — machine tools, jewelry, mining, they are used in cutting, polishing, grinding, drilling.