The action of pressure on solid molecular structures

The action of pressure on fluids modifies the range of internal motions, leading to reorganization phenomena and even to the notion of liquid-liquid phase transitions cf. . The effect of pressure on solids is an extension of what has been described for fluids. The main difference lies in the pressure values applied, which can reach several teraspascals in static conditions. At this level, the electronic environment of atoms is disturbed and the properties of matter are modified. This has led to the discovery of unsuspected phenomena, challenging well-established concepts such as the notion of the solid-solid critical point, molecular dissociation and, above all, a very wide range of new forms of phase transitions. This last point opens up prospects both for a better understanding of the interior of celestial objects and for the emergence of new functional materials. Over the past twenty years, important developments in this field have been made possible by Diamond Anvil Cell (DAC) technology and shockwave experiments. However, it is important to point out to the reader that experiments carried out at such pressures take place in extremely small volumes (< 10 ^-3 mm ³ ) with high pressure gradients (and temperature gradients in pressure-temperature experiments). These reservations cast no doubt on the perfectly reproducible phenomena observed, but do not allow us to conclude with certainty on the physico-chemical stages followed between the initial and final states observed. This is why the scientific community is currently focusing both on the design of devices enabling experiments to be carried out on "large" volumes (> 1 mm ³ ) and on greater use of shock techniques.