Scientists Have Been Arguing About The Structure Of Tungsten Tetraboride For 60 Years. It Turned Out That It Doesn't Exist
Russian scientists have found out how superhard tungsten tetraboride (WB4) – a compound of four boron atoms and one tungsten atom, the structure of which scientists have been arguing for more than half a century. It turned out that this is not a unique compound, but a variety of recently synthesized tungsten pentaboride, the press service of the SKOLKOVO Institute of science and technology writes. The results of the research are available in the scientific journal Advanced Science.
"The mystery of WB4 is solved completely: we have a detailed description of this material and its structure. We know the full range of chemical compositions that it can have and its properties. There are other interesting problems ahead for theorists," commented Artem Oganov, one of the authors of the paper, a Professor at the SKOLKOVO Institute of science and technology.
Chemists and materials scientists around the world have long dreamed of creating methods and tools that can be used to create materials with certain properties, based only on theoretical calculations and knowledge about the properties of individual chemical elements. If such technologies appear, they will make a real revolution in industry and science.
The first step to solving this problem, as Oganov notes, was made in 2006. Then his team developed the USPEX algorithm, which allows you to quickly and accurately calculate the properties of crystals of different substances at very different temperatures and pressures using a chemical formula and element names. Later, Russian chemists improved this method by "teaching" it to work without a given composition, as well as speeding it up with the help of neural networks.
Recently, with the help of USPEX, Oganov and his colleagues have shown that materials harder than diamond can not exist in principle, and have also discovered several boron compounds that are superior in some physical and mechanical parameters even to the winner-an alloy of tungsten, carbon, and cobalt.
Super hard riddle
Having solved this problem, scientists became interested in one of the oldest puzzles related to superhard materials. They tried to figure out the structure of tungsten tetraboride. It was discovered in the middle of the XX century, but the structure of scientists have not been able to determine until now. The fact is that certain differences in the properties of boron and tungsten do not allow you to directly "photograph" the position of the atoms in the thickness of this substance, as well as to understand how evenly they are distributed inside.
Oganov and his colleagues tried to solve this problem by calculating the structure of different WB4 variations using algorithms and comparing these results with experimental data. It turned out that WB4 doesn't really exist.
In fact, this substance is one of the variations of tungsten pentaboride, a material that Oganov and his colleagues discovered several years ago and synthesized at the Institute of high-pressure physics of the Russian Academy of Sciences. It turned out that this substance contains not four boron atoms for every atom of tungsten, but 4.18 or 4.86 atoms. Therefore, scientists suggested renaming it from WB4 to WB5-x.
Since WB5-x is fairly easy to synthesize, its mechanical properties and stability at high temperatures make IT a promising alternative to tungsten carbide composites, which have been most commonly used in many technologies over the past 90 years, Oganov and his colleagues conclude.