Micro-explosion reveals new super-dense aluminium

The method to create high-density phase by the ultrashort laser pulse triggered and spatially confined microexplosion. A tightly focused femtosecond pulse generates hot plasma in sapphire, which in turn produces a strong shock wave, which compresses the material against the surrounding pristine Al2O3 crystal into a densified amorphous phase

Researchers including scientists from The Australian National University have created a new, super-dense version of aluminium that could lead to efficient production of new super-hard nanomaterials at a relatively low cost.In a paper published today in Nature Communications, the group has described how they discovered a way to produce body-centred-cubic aluminium, which is 40 per cent more dense. Super-hard aluminium was predicted to exist more than 30 years ago but has never before been observed.

Lab experiments on producing high pressure and temperature generally use a diamond anvil with a point on one end to produce high pressure but this is limited by the strength of the diamond, which in the case of aluminium, is not hard enough to crush into a new state

Nature Communications – Evidence of superdense aluminium synthesized by ultrafast microexplosion

At extreme pressures and temperatures, such as those inside planets and stars, common materials form new dense phases with compacted atomic arrangements and unusual physical properties. The synthesis and study of new phases of matter at pressures above 100 GPa and temperatures above 10,000 K—warm dense matter—may reveal the functional details of planet and star interiors, and may lead to materials with extraordinary properties. Many phases have been predicted theoretically that may be realized once appropriate formation conditions are found. Here we report the synthesis of a superdense stable phase of body-centred-cubic aluminium, predicted by first-principles theories to exist at pressures above 380 GPa. The superdense Al phase was synthesized in the non-equilibrium conditions of an ultrafast laser-induced microexplosion confined inside sapphire (α-Al2O3). Confined microexplosions offer a strategy to create and recover high-density polymorphs, and a simple method for tabletop study of warm dense matter.

“We demonstrated that it is possible to create extreme pressure and temperature conditions in table-top laboratory experiments using an extremely short laser pulse to create a huge concentration of energy in a very short time and in a very small sub-micron volume inside a sapphire crystal, which is aluminium oxide.

“This experiment resulted in something like a micro-explosion which turned the aluminium to a plasma state that swelled but had nowhere else to go, creating gigantic pressure and dramatic changes in surrounding material properties and producing unfamiliar x-ray spectral lines.

To conclude, this study shows that a femtosecond laser-induced microexplosion confined inside sapphire leads towards synthesis of a new and previously unobserved dense bcc-Al phase, which survives in a compressed state after fast quenching. The route of synthesis is via spatial separation of Al and O ions in short-lived hot non-equilibrium plasma of solid state density. We have demonstrated that high energy density produced in a simple tabletop experiment makes it possible to form an exotic high-density material phase, which could not be produced by other means. The mechanism responsible for the formation of the new phase of material can occur in a wide range of other materials that could be similarly subjected to extreme pressure and temperature conditions and converted into spatially confined plasma. As ultrafast lasers can operate at very high repetition rates within the MHz-range and deliver a high pulse energy, laser-induced microexplosions offer a new strategy for the synthesis of high-pressure phases of materials in useful amounts in table-top laboratory conditions.

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