Physicists of the Max-Planck-Institut für Eisenforschung are able to predict the properties of structural and functional materials with hitherto unprecedented accuracy.
Point defects, for example missing atoms (so called vacancies) significantly influence the performance and durability of modern materials. Even smallest defect concentrations of 1:100,000 can affect the properties of microelectronic devices like processors, solar cells and structural materials like steel.
The picture shows the distribution of atoms next to a defect in a copper crystal at its melting point (1084° C). The green spots show the positions of the atoms at the absolute zero point. The dashed grey circle in the middle shows a lattice vacancy, a place where one atom is missing in the lattice. At high temperatures the atoms vibrate around their lattice position, illustrated by the black cloud.
The results of the Max Planck scientists show a significantly different distribution (orange clouds) by considering the interaction of lattice vibrations. The atoms vibrate closer to the vacancy with increasing temperatures. This leads to a change in energies and vacancies and thereby to a higher defect concentration.
Matter is made out of atoms, which form in the case of crystalline materials a highly ordered lattice. However, the individual atoms do not sit motionless on their lattice sites, but vibrate with an extremely high frequency around their positions – scientists therefore speak about lattice vibrations.
To analyse the concentration of defects in a material and draw conclusions about the materials behaviour, there were until now two possible strategies: Theoretical physicists calculated the energy of the lattice-defect formation, which is directly linked to the number of defects, but their methods were limited to the absolute zero point, i.e. to -273.15 °C.
Experimentalists, on the other hand, measured defect concentrations at high temperatures (above 300 °C). In fact, there was always a large temperature range without available data. As a matter of fact, it is exactly this range around room temperature that is important for materials that are used in our everyday life.
Physicists in the department ‘Computational Materials Design’ at the Max-Planck-Institut für Eisenforschung (MPIE) now achieved a breakthrough in the development of computer simulations that are also able to describe this missing temperature range.
“Established methods for the energetics of lattices were previously not able to include the complex interaction of different modes of lattice vibrations. Thanks to various methodical breakthroughs, we are now able to remove this shortcoming for all relevant temperatures. And we were surprized to see how significantly these temperature-dependent interactions influence the amount of defects in a material”, explains Albert Glensk, doctoral student at the MPIE.
“Formerly predicted results for defects in crystalline materials have to be corrected now. Our calculations show that actual defect energies might easily be about 20% lower than previous estimates. More importantly, we are now for the first time able to close the gap between theory and experiment. All experimental data can be perfectly described with our theory”, concludes Glensk.
With these new insights, scientists are able to calculate and predict precisely how many point defects a material has at a certain temperature and derive conclusions about the performance of a material. This serves as an additional corner stone for the optimization of basic materials on the computer and the prediction of their potential failures as well as strategies to avoid them in production processes.
A. Glensk; B. Grabowski; T. Hickel; J. Neugebauer: Breakdown of the Arrhenius Law in Describing Vacancy Formation Energies: The Im-portance of Local Anharmonicity Revealed by Ab initio Thermody-namics. Physical Review X 4 (2014) 011018. American Physical So-ciety.
Yasmin Ahmed Salem | Max-Planck-Institut für Eisenforschung GmbH
Interstellar seeds could create oases of life
28.08.2015 | Harvard-Smithsonian Center for Astrophysics
Draw out of the predicted interatomic force
28.08.2015 | Hiroshima University
Longer, more severe, and hotter droughts and a myriad of other threats, including diseases and more extensive and severe wildfires, are threatening to transform some of the world's temperate forests, a new study published in Science has found. Without informed management, some forests could convert to shrublands or grasslands within the coming decades.
"While we have been trying to manage for resilience of 20th century conditions, we realize now that we must prepare for transformations and attempt to ease...
A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.
The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...
A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).
Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...
In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.
These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...
Bacteria do not cease to amaze us with their survival strategies. A research team from the University of Basel's Biozentrum has now discovered how bacteria enter a sleep mode using a so-called FIC toxin. In the current issue of “Cell Reports”, the scientists describe the mechanism of action and also explain why their discovery provides new insights into the evolution of pathogens.
For many poisons there are antidotes which neutralize their toxic effect. Toxin-antitoxin systems in bacteria work in a similar manner: As long as a cell...
20.08.2015 | Event News
20.08.2015 | Event News
19.08.2015 | Event News
31.08.2015 | Awards Funding
31.08.2015 | Materials Sciences
31.08.2015 | Materials Sciences