14 December 2022 ESRFnews
ORDINARY conditions, as they seem to us, are really far from being so. Most of the universe s visible condensed matter does not exist in the benign climes of Earth s lower atmosphere, but inside planets and other celestial objects, at far greater temperatures and billions of times more pressure. It is no surprise that such extreme conditions are a treasure trove for new materials materials whose properties are very different, and perhaps more useful to humans. Take carbon, for example. On Earth, its most thermo-
dynamically stable form is graphite, in which each carbon atom is bonded to three others, in layers. Deep in the Earth s interior, however, strong heat and pressures upwards of 50,000 atmospheres force the carbon atoms closer together until they overcome an energy barrier
to settle into a new structural state: diamond, in which each carbon atom is bonded tetrahedrally to four others. Diamond is an example of a metastable state once formed, it does not revert to graphite when it is brought back into benign conditions. As a result, we can exploit the way it refracts and disperses light to make jewellery, or its hardness to make cutting and polishing tools. Fortunately, scientists do not need planetary interiors
to access extreme conditions. Another application of diamond is the diamond anvil cell (DAC), in which a pair of diamonds compress tiny samples of different starting materials to incredible pressures. DACs are part of the standard toolkit for high-pressure scientists, but what
goes on inside them is invisible: the sample sits within a gasket and, once compressed, becomes incredibly tiny and more or less opaque to all but the highest energy photons. The goal to synthesise new, metastable, functional materials can therefore only be pursued at synchrotrons. And the ESRF EBS is leading the way. In June
this year, a team led by the University of Bayreuth in Germany employed an advanced, double stage DAC which, in combination with laser heating, synthesised a rhenium nitrogen alloy at record-breaking pressures verging on one terapascal three times those at the centre of the Earth. The X-rays available at the ESRF s
A hunt for new engineering materials is taking place at the ESRF, which is opening up new frontiers for research at high pressures and temperatures.
FUNCTIONAL MATERIALS
Extreme synthesis
The ESRF has been pioneering extreme-conditions research since the 1990s, and with the EBS upgrade has been pushing it to new frontiers