Browsing by Author "Chathoth, SM"

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    The influence of short-range structures on atomic caging in glass-forming Cu-Zr-Al melts
    (Elsevier, 2018-11) Wong, KK; Kan, HW; Mole, RA; Yu, DH; Chathoth, SM
    Atomic caging is an important dynamic process that influences liquid vitrification. In this article, we have studied bulk glass-forming copper-zirconium-aluminum (Cu-Zr-Al) systems using quasielastic neutron scattering and molecular dynamics simulation in order to understand the influence of short-range structures on atomic caging. We found that, in Cu-Zr-Al melts, the long range atomic transport process occurs via a jump diffusion process, and temperature dependence of the atomic diffusion process is non-Arrhenius. Furthermore, the Cu diffusion coefficient at a given temperature decreases with Al addition. Inherent structures obtained from molecular dynamic simulation trajectories show that the dominant short range structures above the melting temperature of these melts are 〈0,3,6,4〉 and 〈0,2,8,2〉 and the percentage of these structure increases with decreasing temperature. The residence time of the atoms in the cage was found to be directly correlated with the number of dominant short-range structures in these melts. Our results show that transient local short-range structures have a strong influence on atomic caging in the glass-forming metallic melts. © 2018 Elsevier Ltd.
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    The logarithmic relaxation process and the critical temperature of liquids in nano-confined states
    (International Conference on Neutron Scattering, 2017-07-12) Chathoth, SM; Chen, C; Yu, DH
    The logarithmic relaxation process is the slowest of all relaxation processes and is exhibited by only a few molecular liquids and proteins. Bulk salol, which is a glass-forming liquid, is known to exhibit logarithmic decay of intermediate scattering function for the ?-relaxation process. Here, we report the influence of nanoscale confinements on the logarithmic relaxation process and changes in the microscopic glass-transition temperature of salol in the carbon and silica nanopores. The generalized vibrational density-of-states of the confined salol indicates that the interaction of salol with ordered nanoporous carbon is hydrophilic in nature whereas the interaction with silica surfaces is more hydrophobic. The mode-coupling theory critical temperature derived from the QENS data shows that the dynamic transition occurs at much lower temperature in the carbon pores than in silica pores. The results of this study indicate that, under nano-confinements, liquids that display logarithmic ?-relaxation phenomenon undergo a unique glass transition process.
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    The role of local-geometrical-orders on the growth of dynamic-length-scales in glass-forming liquids
    (Springer Nature, 2018-12-01) Wong, K; Krishnan, RP; Chen, C; Du, Q; Yu, DH; Lu, Z; Samwer, K; Chathoth, SM
    The precise nature of complex structural relaxation as well as an explanation for the precipitous growth of relaxation time in cooling glass-forming liquids are essential to the understanding of vitrification of liquids. The dramatic increase of relaxation time is believed to be caused by the growth of one or more correlation lengths, which has received much attention recently. Here, we report a direct link between the growth of a specific local-geometrical-order and an increase of dynamic-length-scale as the atomic dynamics in metallic glass-forming liquids slow down. Although several types of local geometrical-orders are present in these metallic liquids, the growth of icosahedral ordering is found to be directly related to the increase of the dynamic-length-scale. This finding suggests an intriguing scenario that the transient icosahedral connectivity could be the origin of the dynamic-length-scale in metallic glass-forming liquids. © The Author(s) 2018. Open Access - This article is licensed under a Creative Commons Attribution 4.0 International License.