Using theoretical methods, an international group of scientists led by Artem R. Oganov, Professor of Skoltech, Stony Brook University and Moscow Institute of Physics and Technology predicted unusual from the point of view of classical chemistry nitrides of hafnium and chromium with the chemical formulae HfN10 (and its zirconium analogue ZrN10) and CrN4. These compounds can be obtained at relatively low pressures and contain high-energy groups of nitrogen atoms.
Pure polymeric nitrogen is the ideal high-energy compound that packs so much energy per unit volume or mass that it could be used as a powerful explosive if it were not for gigantic pressures of its synthesis. This work shows that nitrogen polymerizes at much lower pressures in presence of metal ions, and such compounds might find practical use. The authors also predicted a range of new hafnium nitrides as well as nitrides, carbides and borides of chromium, with an unusual combination of properties (high hardness, electrical conductivity, and toughness).
Superhard materials can be divided into two main classes: compounds of boron, carbon, nitrogen and oxygen together and compounds of transition metals with boron, carbon and nitrogen. The scientists studied four systems in two simultaneously published works: hafnium-nitrogen, chromium-nitrogen, chromium-carbon and chromium-boron.
Several new materials, which can be formed at relatively low pressure, were predicted. Among them there are materials with an unusual combination of very high hardness and electrical conductivity. In particular, newly predicted carbide Cr2C should even be stable at atmospheric pressure; and researchers were able to resolve for the first time the crystal structure of a known compound Cr2N.
The most interesting finding is the chemical compound with the formula HfN10 - here, there are ten nitrogen atoms per hafnium atom. Its structure is very peculiar from a chemical point of view: The hafnium atoms and N2 molecules are sandwiched between infinite chains of nitrogen atoms. Such structure is formed under relatively low pressure of 0.23 Mbar.
According to Professor Artem R. Oganov: "This finding brings us back to one of the Holy Grails in material science, the search for polymeric nitrogen, an ideal high-energy-density material".
The fact of the matter is that all good explosive compounds contain nitrogen - at the moment of explosion the nitrogen atoms form the extraordinary stable N2 molecule, releasing a vast amount of energy. The more nitrogen atoms in a compound, and the more unusual their bonding, the more energy will be released as a result of the explosion. Polymeric nitrogen was first predicted by American physicist C. Mailhiot in 1992 and then synthesized in 2004 by Russian physicist Michael Eremets under pressures exceeding one million atmospheres.
At such pressures only micron-sized samples can be made, which rules out any practical applications. Professor Oganov says: "Our group works on several projects related to metal polynitrides. This is a promising class of high-energy-density compounds, requiring much lower pressures than pure polymeric nitrogen (e.g., 5 times lower in case of HfN10, or even less for CrN4, and this is likely not the limit). Chemists have long dreamed about synthesising polymeric nitrogen in large quantities. We have proposed the compound class that can fulfil this dream. "
Two publications appeared as a result of these studies. The first author of the article published in The Journal of Physical Chemistry Letters is Alexander Kvashnin, a postdoc at Skoltech. The first author of the second article in Physical Review B is Jin Zhang, Oganov's graduate student at Stony Brook University.
The Skolkovo Institute of Science and Technology (Skoltech) is a private graduate research university. Established in 2011 in collaboration with the Massachusetts Institute of Technology (MIT), Skoltech educates global leaders in innovation, advance scientific knowledge, and fosters new technologies to address critical issues facing Russia and the world. Skoltech conducts it work integrating the best practices of the best Russian and international educational and scientific research universities. Moreover, the university pays particular attention to entrepreneurship and innovative education. Website: http://www.
Asya Shepunova | EurekAlert!
Don't Give the Slightest Chance to Toxic Elements in Medicinal Products
23.03.2018 | Physikalisch-Technische Bundesanstalt (PTB)
North and South Cooperation to Combat Tuberculosis
22.03.2018 | Universität Zürich
Satellites in near-Earth orbit are at risk due to the steady increase in space debris. But their mission in the areas of telecommunications, navigation or weather forecasts is essential for society. Fraunhofer FHR therefore develops radar-based systems which allow the detection, tracking and cataloging of even the smallest particles of debris. Satellite operators who have access to our data are in a better position to plan evasive maneuvers and prevent destructive collisions. From April, 25-29 2018, Fraunhofer FHR and its partners will exhibit the complementary radar systems TIRA and GESTRA as well as the latest radar techniques for space observation across three stands at the ILA Berlin.
The "traffic situation" in space is very tense: the Earth is currently being orbited not only by countless satellites but also by a large volume of space...
An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.
The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...
In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.
Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...
Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.
They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...
A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...
23.03.2018 | Event News
19.03.2018 | Event News
16.03.2018 | Event News
23.03.2018 | Materials Sciences
23.03.2018 | Agricultural and Forestry Science
23.03.2018 | Physics and Astronomy