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School of Physics and Astronomy

Liquid-like metals under pressure

There is currently a surge of interest in mechanical behaviour of nanoscale systems with the aim to understand if metastability in a variety of materials can be achieved, explained and indeed exploited.

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Since the dawn of nanotechnology it has been known that size effects have significant consequences for the atomic arrangements, electronic properties and behavior of matter under extreme pressure. It has been shown that exploring size effect is crucial for understanding mechanical properties of materials.  Furthermore, behavior of matter under critical pressure–temperature conditions provides vital guidance in the search for materials with novel properties. Researchers at the CCMMP group have recently observed remarkable behavior of small (under ∼5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We show that contrary to the expected high pressure transition sequence and behaviour, small matrix-free Ge nanoparticles undergo a transition to a liquid-like metallic structure. A combination of synchrotron radiation methods (x-ray diffraction, x-ray absorption) and in-house spectroscopic techniques (Raman and photoluminescence) together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase—amorphous metallic Ge. From the fundamental viewpoint, the phenomenon of high pressure amorphization enables one to explore thermodynamics and kinetics of transformations in metastable systems (such as glasses). Besides, the phenomenon of pressure-induced amorphization is of interest from the practical point of view as it provides access to structures with novel electronic, optical, and mechanical properties.