arXiv subjects

Birte Riechers

Publications and source records attributed to Birte Riechers.

4 recordsLinked to original sources

arXiv2026

Microstructure-specific mechanisms define multistage relaxation dynamics in a metallic model-glass

Deciphering complex relaxation pathways in disordered solids is a central challenge across polymeric, oxide, and metallic glasses, which traditionally relies on the interpretation of mechanical spectroscopy and resulting damping modes. Here we demonstrate the direct observation of dominant atomic-scale relaxation mechanisms during isothermal annealing of an as-quenched binary model glass towards incipient crystallization. Assessed via simulated x-ray photon correlation spectroscopy, a multi-state structural decorrelation is uncovered via speckle-pattern analysis of the full three-dimensional diffraction sphere across the first peak of the structure factor. Over a simulation time of up to 10 $μ$s, three distinct and subsequent decorrelation stages of thermal vibration, glassy network evolution, and structural and chemical ordering towards crystallization are identified. These findings promote a picture where specific dynamically-separated mechanisms drive the microstructural evolution during glass relaxation and suggest a much richer multi-mode relaxation behavior of metallic glasses than hitherto identified.

cond-mat.mtrl-sci↗

arXiv2022

Predicting nonlinear physical aging of glasses from equilibrium relaxation via the material time

The noncrystalline glassy state of matter plays a role in virtually all fields of materials science and offers complementary properties to those of the crystalline counterpart. The caveat of the glassy state is that it is out of equilibrium and therefore exhibits physical aging, i.e., material properties change over time. For half a century, the physical aging of glasses has been known to be described well by the material-time concept, although the existence of a material time has never been directly validated. We do this here by successfully predicting the aging of the molecular glass 4-vinyl-1,3-dioxolan-2-one from its linear relaxation behavior. This establishes the defining property of the material time. Via the fluctuation-dissipation theorem, our results imply that physical aging can be predicted from thermal-equilibrium fluctuation data, which is confirmed by computer simulations of a binary liquid mixture.

cond-mat.soft↗

arXiv2021

Time-scale coupling in hydrogen- and van der Waals-bonded liquids

The coupling behavior of time scales of structural relaxation is investigated on the basis of five different response functions for 1,2,6-hexanetriol, a hydrogen-bonded liquid with a minor secondary contribution, and 2,6,10,15,19,23-hexamethyl-tetracosane (squalane), a van der Waals bonded liquid with a prominent secondary relaxation process. Time scales of structural relaxation are derived as inverse peak frequencies for each investigated response function. For 1,2,6-hexanetriol, the time-scale indices are temperature-independent, while a decoupling of time scales is observed for squalane in accordance with literature. An alternative evaluation approach is made on the squalane data, extracting time scales from the terminal relaxation mode instead of the peak position, and in this case temperature-independent coupling is also found for squalane, despite its strong secondary relaxation contribution. Interestingly, the very same ordering of response-function-specific time scales is observed for these two liquids, which is also consistent with the observation made for simple van der Waals bonded liquids reported previously [Jakobsen \textit{et al.}, J. Chem. Phys. \textbf{136}, 081102 (2012)]. This time-scale ordering is based on the following response functions, from fast to slow dynamics: shear modulus, bulk modulus, dielectric permittivity, longitudinal thermal expansivity coefficient, and longitudinal specific heat. These findings indicate a general relation between the time scales of different response functions and, as inter-molecuar interactions apparently play a subordinate role, suggest a rather generic nature of the process of structural relaxation.

cond-mat.soft↗

arXiv2016

Emergent Inter-particle Interactions in Thermal Amorphous Solids

Amorphous media at finite temperatures, be them liquids, colloids or glasses, are made of interacting particles that move chaotically due to thermal energy, colliding and scattering continuously off each other. When the average configuration in these systems relaxes only at long times, one can introduce {\em effective interactions} that keep the {\em mean positions} in mechanical equilibrium. We introduce a new framework to determine these effective force-laws that define an effective Hessian that can be employed to discuss stability properties and density of states of the amorphous system. We exemplify the approach with a thermal glass of hard spheres; these feel zero forces when not in contact and infinite forces when they touch. The present approach recaptures the effective interactions which for sufficiently dense spheres at temperature $T$ depends on the gap $h$ between spheres as $T/h$ [C. Brito and M. Wyart, Europhys. Lett. 76 149 (2006)]. In systems at lower densities or with longer microscopic interaction (say like Lennard-Jones), the emergent force laws will include ternary, quaternary and generally higher order many-body terms, even if the microscopic interactions are strictly binary.

cond-mat.soft↗