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
Hope to discover sure signs of life on Mars? New research says look for the element vanadium
22.09.2017 | University of Kansas
22.09.2017 | Forschungszentrum MATHEON ECMath
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
22.09.2017 | Life Sciences
22.09.2017 | Medical Engineering
22.09.2017 | Physics and Astronomy