Osmium
Under pressure
Osmium rivals diamonds: an international research team led by the University of Bayreuth has applied the highest pressure ever achieved in a laboratory to the platinum metal osmium. The scientists compressed the element to up to 770 gigapascals in a specially developed diamond anvil cell. This force is more than twice the pressure that prevails in the Earth’s interior. The experiment not only broke the existing world record for high pressure, but also surprised the researchers with two findings: even under extreme conditions, osmium remains structurally stable, but develops previously unknown interactions within its electron shells.
Platinum metal Osmium – an extreme element
Osmium is one of the most fascinating elements in the Periodic Table. This heavy metal, which has a bluish sheen in its pure form, is the densest naturally occurring element with a density of 22.587 g/cm³, has one of the highest binding energies and one of the highest melting points. It is rarely found in the Earth’s crust and is much rarer than gold. It usually occurs as an alloy or accompanying material in ore or other precious metals such as platinum, iridium or rhodium. Due to its extreme properties, the metal is as difficult to compress as a diamond. Osmium is therefore used when special quality, hardness and stability are required. For example, in alloys for electrical contacts, in heavily used machine parts or as a nib in high-quality fountain pens.
New high-pressure method: diamond anvil cell combined with X-rays
Scientists had previously tested the extraordinary compressibility of osmium, but only at a pressure of 75 gigapascals, about one-fifth of the Earth’s core pressure. In order to test the resilience of osmium at a new level, the research team led by Professor Natalia Dubrovinskaia and Professor Leonid Dubrovinsky, with the participation of a DESY research team (Deutsches Elektronen-Synchrotron, Hamburg), developed a special, innovative apparatus: a two-stage diamond anvil cell. Their individual, tiny stamps are made of nanocrystalline diamond and each have a diameter of only ten to 20 micrometres. The numerous grain boundaries of the nanocrystals make the micro-stamps harder than single-crystal diamonds – they can withstand and transmit almost twice the pressure, at 770 gigapascals.
In order to track how the atomic structure of osmium behaves in detail under this extreme pressure, the research team collaborated with several large research facilities that have high-intensity X-ray equipment: the DESY research light source PETRA III, the European Synchrotron Radiation Facility ESRF in France and the Advanced Photon Source in the USA were used.
Osmium remains atomically stable
High-resolution X-ray measurements of the pressure tests conducted with the diamond anvil cell revealed something astonishing: while high pressure fundamentally changes the properties of many materials – for example, by making oxygen solid and electrically conductive – osmium retains its hexagonal crystal structure even under extreme high pressure. Pressures of 770 gigapascals merely cause the volume per unit cell in the osmium lattice to shrink. However, contrary to the research group’s expectations, the atomic stability of the element remains unchanged.
Under high pressure: subtle anomalous electron behaviour
However, the world record pressure experiment did not leave the platinum metal completely unscathed. Precise X-ray analyses revealed two subtle anomalies in the crystal lattice at approximately 150 and 440 gigapascals. According to the research team, the first deviation was caused by a redistribution of the outer osmium electrons. This is a reaction to pressure that also occurs in other elements and can change the material properties.
The electron reaction at around 440 gigapascals attracted more attention. The pressure inside the element increased to such an extent that the electron shells of the individual atoms overlapped. As a result, even the core-proximal orbitals 5p and 4f, which normally do not participate in interactions or bonds, can react with each other. The research group concluded that extreme high pressure can indeed alter the properties of core electrons.
New perspectives for experimental physics and materials research
The high-pressure world record set with the rare platinum metal osmium impressively shifts the previous boundaries of experimental physics in answering the question: how does highly compressed matter behave and change? Using a specially developed two-stage diamond anvil cell in combination with high-resolution X-rays, it is now possible to investigate material states that were previously only calculable in theory. For example, the collected data and findings can help researchers analyse the structure of large rock slabs and realistically model the processes inside planets and large stars. What’s more, the observation that even electrons close to the nucleus can interact opens up new perspectives. The researchers believe that the pressure experiment could help to develop new functional materials that can withstand extreme conditions.
For insights that surprise you and open up new perspectives: Carl ROTH equips you with aids for all aspects of research and laboratory work. Please visit our online shop: www.carlroth.com
Sources:
https://www.chemie.de/news/154246/hochdruck-weltrekord-forscher-quetschen-osmium-aus.html
https://pro-physik.de/nachrichten/hochdruck-weltrekord-forscher-quetschen-osmium-aus
https://www.scinexx.de/news/technik/hochdruck-rekord-osmium-bleibt-standhaft
