A microscopic picture of the atomic motion during polyamorphism in an ultra-viscous liquid

Speaker

• Beatrice Ruta, CNRS, Institut Lumière Matière, Lyon (FR)

Abstract

Many materials, ranging from monatomic liquids to molecular systems and metallic glasses show transitions between different amorphous phases whose origin is still unknown [1]. In glass-formers, polyamorphism appears related to kinetic properties of the liquids, still not direct evidence of this has been reported so far. 
We present here the microscopic evidence of a connection between a liquid-liquid transition (LLT) and a fragile-to-strong dynamical crossover between ultra-viscous metallic liquids. For this purpose, we merged state-of-the-art synchrotron techniques, like high-energy X-ray diffraction and X-ray Photon Correlation Spectroscopy, with an unconventional protocol consisting in a quasi-static cooling of a supercooled liquid. With this approach, we have been able to observe a polyamorphic transition between two liquid structures with different kinetics whose origin appears related to an ordering process not involving density changes [2]. 
The wave-vector dependence of the dynamics in the low temperature strong phase reveals a peculiar slowdown of the main relaxation process at the inter-particle distance, reminiscent of the de Gennes narrowing found in the frequency domain for simple liquids [3]. This behavior is accompanied by the occurrence of dynamical heterogeneities on faster times scales and suggests the existence of a peculiar mechanism of hopping of caged particles for the atomic motion.

[1] Murata, K. & Tanaka, H. Nat. Mat. 11, 436, 2012
[2] S. Hechler et al. Phys. Rev. Mat. 2, 085603, 2018
[3] B. Ruta et al. Phys. Rev. Lett. 125, 055701, 2020

Who is Beatrice Ruta?

Beatrice Ruta is a CNRS researcher at the Institut Lumière Matière in Lyon, France. Her main research activity aims at understanding the dynamical properties of complex systems, like glasses and gels studied with synchrotron radiation.

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