Papers by rithin krishnan
Journal of Materials Science & Technology, 2019
Quasielastic neutron scattering (QENS) has been used to study the atomic relaxation process and m... more Quasielastic neutron scattering (QENS) has been used to study the atomic relaxation process and microscopic transport mechanism in high-entropy glass-forming metallic (HE-GFM) liquids. Self-intermediate scattering functions obtained from the QENS data show unusually large stretching, which indicates highly heterogeneous atomic dynamics in HE-GFM liquids. In these liquids, a group of atoms over a length scale of about 21 Å diffuses collectively even well above the melting temperature. However, the temperature dependence of diffusion process in one of the HE-GFM liquid is Arrhenius, but in the other HE-GFM liquid it is non-Arrhenius. Although the glass-forming ability of these HE-GFM liquids is very poor, the diffusion coefficients obtained from the QENS data indicate the long range atomic transport process is much slower than that of the best metallic glass-forming liquids at their melting temperatures.
Journal of Materials Science & Technology, 2019
Quasielastic neutron scattering (QENS) has been used to study the atomic relaxation process and m... more Quasielastic neutron scattering (QENS) has been used to study the atomic relaxation process and microscopic transport mechanism in high-entropy glass-forming metallic (HE-GFM) liquids. Self-intermediate scattering functions obtained from the QENS data show unusually large stretching, which indicates highly heterogeneous atomic dynamics in HE-GFM liquids. In these liquids, a group of atoms over a length scale of about 21 Å diffuses collectively even well above the melting temperature. However, the temperature dependence of diffusion process in one of the HE-GFM liquid is Arrhenius, but in the other HE-GFM liquid it is non-Arrhenius. Although the glass-forming ability of these HE-GFM liquids is very poor, the diffusion coefficients obtained from the QENS data indicate the long range atomic transport process is much slower than that of the best metallic glass-forming liquids at their melting temperatures.
The precise nature of complex structural relaxation as well as an explanation for the precipitous... more 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 ordering could be the origin of the dynamic-length-scale in metallic glass-forming liquids.
Scientific reports, Jan 31, 2018
The precise nature of complex structural relaxation as well as an explanation for the precipitous... more 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.
RSC Advances, 2017
The dynamic processes of 2-biphenylmethanol (BPM) confined in carbon and silica pores with differ... more The dynamic processes of 2-biphenylmethanol (BPM) confined in carbon and silica pores with different sizes have been studied using the quasi-elastic neutron scattering (QENS) technique. A β-relaxation process following a logarithmic decay was found in both the nano-confined states. The peculiar features of the observed dynamic processes strongly agree with the predictions of the mode-coupling theory (MCT) for higher-order glass-transition singularities. The MCT critical temperature (Tc) of BPM, when confined in carbon and silica pores, was evaluated. The Tc was significantly low in the nano-confined states as compared to the bulk states. Furthermore, when comparing BPM confined in similar pore-sized carbon and silica materials, it was observed that the Tc was much lower for BPM confined in nano-porous silica materials. The generalized vibrational density-of-states of confined BPM indicated that the interactions of BPM with the silica pores is hydrophobic, whereas the interactions wi...
Physical Review B
Logarithmic relaxation is a unique relaxation process exhibited by a few molecular liquids and bi... more Logarithmic relaxation is a unique relaxation process exhibited by a few molecular liquids and biomolecules. However, the microscopic origin of logarithmic relaxation is still unclear. To understand the origin of this process, we studied two liquids that exhibit logarithmic relaxation in a dissolved state using quasielastic neutron scattering (QENS) and depolarized dynamic light scattering (DDLS). Although the intermolecular potential of the liquids is drastically different in the dissolved state from the bulk liquids, we observed that the logarithmic relaxation still persists. Our results indicate that the intermolecular potential does not play a role in determining the logarithmic relaxation process. The coupling of rotational and translational relaxation processes could be the origin of the logarithmic relaxation process exhibited by the molecular liquids.
Acta Materialia
Abstract Supercooled liquids and glasses, due to their intrinsically unstable nature, are known t... more Abstract Supercooled liquids and glasses, due to their intrinsically unstable nature, are known to relax continuously until an equilibrium state is reached. By exploring atomic relaxation, aging and microscopic structure of chemically similar but physically dissimilar metallic glasses, we find that neither the relaxation time nor aging correlate with the free volume or density of the glasses. Furthermore, atomic relaxation time in these metallic glasses does not depend on the microscopic structure of the systems. The activation energy for the diffusion process indicates a completely different microscopic mechanism governing the atomic transport process. Nevertheless, the age-dependent relaxation time surprisingly exhibits a universal time-waiting time-temperature superposition. Our results provide a convincing proof of the universality in the aging of out-of-equilibrium materials.
Journal of Physics D, 2018
Quasi-elastic neutron scattering has been used to study atomic relaxation processes in high-entro... more Quasi-elastic neutron scattering has been used to study atomic relaxation processes in high-entropy glass-forming metallic melts with different glass-forming ability (GFA). The momentum transfer dependence of mean relaxation time shows a highly collective atomic transport process in the alloy melts with the highest and lowest GFA. However, a jump diffusion process is the long-range atomic transport process in the intermediate GFA alloy melt. Nevertheless, atomic mobility close to the melting temperature of these alloy melts is quite similar, and the temperature dependence of the diffusion coefficient exhibits a non-Arrhenius behavior. The atomic mobility in these high-entropy melts is much slower than that of the best glass-forming melts at their respective melting temperatures.
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Papers by rithin krishnan