Subsequent electride structures have been predicted ubiquitous 10, 11. Over the past few years, ab initio calculations have disclosed novel properties of matter in the terapascal (TPa) range, due to pressure-induced interaction between core electrons 9 and to the larger fraction of the volume occupied by core electrons which tends to localize valence electrons within interstitial pockets.

The standard DAC is also a very useful tool to measure the properties of the components of the EarthвЂ™s interiors up to the thermodynamic conditions of its center (363вЂ‰GPa, ~6000вЂ‰K), helping to refine Earth models 8. Over the past two decades, with extensive use of third-generation synchrotrons, the harvest of results has been striking, pressure seems to turn simplicity in complexity, for instance in hydrogen 5, and properties of materials have been pushed to new limits such as a record critical superconducting temperature 6 or a record chemical energy density storage in polymeric nitrogen 7. It should be acknowledged that nowadays a sample under a 100вЂ‰GPa pressure can be characterized in great details. Second, the sample is macroscopic, at least a few Ојm in dimensions, enabling the use of a large portfolio of characterization methods in standard laboratory and in front of synchrotron beamlines. First, the stress state of matter under high static pressure can be well controlled and a quasi-hydrostatic compression of the sample can even be achieved by using a soft solid pressure-transmitting medium or by laser annealing the sample. Yet, the possibility to measure reliably and accurately the properties of matter under ultrahigh static pressure relies on two facts. The use of the DAC has been continuously improved by various developments such as the use of a gasket 2, the anvils bevel shape 3, or better supporting seats 4. This centimeter-sized press squeezes samples between two diamond anvils to reach extreme pressures.

The diamond anvil cell (DAC) was invented to exploit the exceptional properties of diamond in terms of strength and transparency 1. High-pressure physics is an old field for which the process of scientific discovery is driven by new tools.

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