An international team of scientists led by the University of Bayreuth in Germany has created the highest static pressure ever achieved in a lab – 770 Gigapascals (GPa), about 130 GPa higher than the previous world record set by members of the same team.
The researchers used the pressure to investigate the behaviour of osmium, one of the least compressible metals on Earth.
They found osmium does not change its crystal structure even at the highest pressures, but the core electrons of the atoms come so close to each other that they can interact – contrary to what is usually known in chemistry.
This study was published in the journal Nature and has implications for understanding physics and chemistry of highly compressed matter, for design of materials to be used at extreme conditions, and for modelling the interiors of giant planets and stars.
Metallic osmium (Os) is one of the most exceptional chemical elements, having at ambient pressure the highest known density of all elements, one of the highest cohesive energies, melting temperatures, and a very low compressibility – it is almost as incompressible as diamond. Due to its hardness, osmium finds applications in alloys used for instance as electrical contacts, wear-resistant machine parts and tips for high-quality ink pens.
“High pressure is known to radically affect properties of chemical elements: metals like sodium may become transparent insulators; gases like oxygen solidify and become electrical conductors – and even superconductors,” explains Natalia Dubrovinskaia from the University of Bayreuth, together with Leonid Dubrovinsky the main author of the study. “as any other material subjected to very high compression, osmium is expected to change its crystal structure.”
For their experiments, the scientists used a device for generating ultra-high static pressures developed by Dubrovinsky and Dubrovinskaia.
The device uses micro-anvils of only 10 to 20 micrometres (a micrometre is a thousandths of a millimetre) in diameter which are made of nanocrystalline diamond bound together.
The many boundaries make the nanocrystalline anvils even harder than single crystal diamonds.
The team then used high-brilliance X-rays to study the osmium sample.
Bill Condie is a science journalist based in Adelaide, Australia.
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