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Wave vector dependence of the dynamics in supercooled metallic liquids
Authors:
B. Ruta,
S. Hechler,
N. Neuber,
D. Orsi,
L. Cristofolini,
O. Gross,
B. Bochtler,
M. Frey,
A. Kuball,
S. S. Riegler,
M. Stolpe,
Z. Evenson,
C. Gutt,
F. Westermeier,
R. Busch,
I. Gallino
Abstract:
We present a detailed investigation of the wave vector dependence of collective atomic motion in Au49Cu26.9Si16.3Ag5.5Pd2.3 and Pd42.5Cu27Ni9.5P21 supercooled liquids close to the glass transition temperature. Using x-ray photon correlation spectroscopy in a precedent uncovered spatial range of only few interatomic distances, we show that the microscopic structural relaxation process follows in ph…
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We present a detailed investigation of the wave vector dependence of collective atomic motion in Au49Cu26.9Si16.3Ag5.5Pd2.3 and Pd42.5Cu27Ni9.5P21 supercooled liquids close to the glass transition temperature. Using x-ray photon correlation spectroscopy in a precedent uncovered spatial range of only few interatomic distances, we show that the microscopic structural relaxation process follows in phase the structure with a marked slowing down at the main average inter-particle distance. This behavior is accompanied by dramatic changes in the shape of the intermediate scattering functions which suggest the presence of large dynamical heterogeneities at length-scales corresponding to few particle diameters. A ballistic-like mechanism of particle motion seems to govern the structural relaxation of the two systems in the highly viscous phase, likely associated to hopping of caged particles in agreement with theoretical studies.
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Submitted 28 August, 2020; v1 submitted 3 March, 2020;
originally announced March 2020.
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Breakdown of the Stokes-Einstein Relation Above the Melting Temperature in a Liquid Phase-Change Material
Authors:
Shuai Wei,
Zach Evenson,
Moritz Stolpe,
Pierre Lucas,
C. Austen Angell
Abstract:
The dynamic properties of liquid phase-change materials (PCMs), such as viscosity $η$ and atomic self-diffusion coefficients D, play an essential role in ultrafast phase switching behavior of novel non-volatile phase-change memory applications, as they are intimately related to crystallization kinetics and phase stabilities. To connect $η$ to D, the Stokes-Einstein relation (SER) is commonly assum…
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The dynamic properties of liquid phase-change materials (PCMs), such as viscosity $η$ and atomic self-diffusion coefficients D, play an essential role in ultrafast phase switching behavior of novel non-volatile phase-change memory applications, as they are intimately related to crystallization kinetics and phase stabilities. To connect $η$ to D, the Stokes-Einstein relation (SER) is commonly assumed to be valid at high temperatures near or above the melting temperature $T_{m}$ and is frequently employed for assessing liquid fragility (or crystal growth velocity) of technologically important PCM compositions. However, using quasi-elastic neutron scattering (QENS), we give here experimental evidence for a breakdown of the SER even at temperatures above $T_{m}$ in the high-atomic-mobility state of a typical PCM, Ge$_{1}$Sb$_{2}$Te$_{4}$, where the decay of density correlation functions still remains exponential. The origin of the breakdown is thus unlikely the result of dynamical heterogeneities, as is usually postulated for viscous liquids. Rather, we discuss its possible connections to a metal-semiconductor and fragile-strong transition hidden below $T_{m}$.
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Submitted 3 May, 2018;
originally announced May 2018.
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Activation energy spectrum for relaxation and polyamorphism in an ultra-viscous metallic glass former
Authors:
Isabella Gallino,
Daniele Cangialosi,
Zach Evenson,
Lisa Schmitt,
Simon Hechler,
Moritz Stolpe,
Beatrice Ruta
Abstract:
Many glass-formers exhibit phase transitions between two distinct liquid states. For some metallic glass-formers, the liquid-liquid transition is experimentally found in the supercooled liquid at intermediate temperature between the melting point and the glass transition temperature Tg. We report here on a liquid-liquid transition in an ultra-viscous metallic glass-former, accessed during long-tim…
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Many glass-formers exhibit phase transitions between two distinct liquid states. For some metallic glass-formers, the liquid-liquid transition is experimentally found in the supercooled liquid at intermediate temperature between the melting point and the glass transition temperature Tg. We report here on a liquid-liquid transition in an ultra-viscous metallic glass-former, accessed during long-time annealing. This study is conducted on the Au49Cu26.9Si16.3Ag5.5Pd2.3 composition with a liquid-liquid transition temperature slightly lower than Tg. The consequence is that the high-temperature kinetically fragile liquid freezes into the glass during conventional processing and the underlying liquid-liquid transition is thus accessed by the system during annealing below Tg. Upon reheating, the reverse transformation is observed by calorimetry. This conclusion is supported by a broad collection of complementary laboratory and synchrotron-based techniques, such as differential- and fast- scanning calorimetry, and x-ray photon correlation spectroscopy. Our findings support the big-picture proposed by Angell that liquids with different fragility occupy different flanks of an underlying order-disorder transition. Furthermore, our multiscale analysis reveals the existence of multiple decays of the enthalpy recovery, which is reflected in the observed microscopic ordering and aging mechanism of the glass through distinct stationary regimes interconnected by abrupt dynamical aging regimes.
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Submitted 8 June, 2017;
originally announced June 2017.
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Liquid-liquid transition revealed by quasi-static cooling of an ultra-viscous metallic liquid
Authors:
S. Hechler,
B. Ruta,
M. Stolpe,
E. Pineda,
Z. Evenson,
O. Gross,
W. Hembree,
A. Bernasconi,
R. Busch,
I. Gallino
Abstract:
Temperature-driven polyamorphism has been reported in various supercooled liquids and glasses. The dynamical and structural routes followed by the system during such crossovers are however not universal and appear to be related to intrinsic kinetic properties of the liquid. By combining x-ray photon correlation spectroscopy and high energy x-ray diffraction, we have followed the collective atomic…
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Temperature-driven polyamorphism has been reported in various supercooled liquids and glasses. The dynamical and structural routes followed by the system during such crossovers are however not universal and appear to be related to intrinsic kinetic properties of the liquid. By combining x-ray photon correlation spectroscopy and high energy x-ray diffraction, we have followed the collective atomic motion and structural changes during quasi-static cooling of the Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glass-former. Due to this ultra-slow thermal protocol, the glass transition temperature is lowered far enough to reveal a liquid-liquid crossover in the ultra-viscous supercooled phase. This transition is usually hidden by vitrification and leads to a strong liquid characterized by increasing correlation at the medium range.
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Submitted 21 April, 2017;
originally announced April 2017.
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Phase separation of a supersaturated nanocrystalline Cu Co alloy and its influence on thermal stability
Authors:
Andrea Bachmaier,
Marina Pfaff,
Moritz Stolpe,
Hisham Aboulfadl,
Christian Motz
Abstract:
The thermal decomposition behavior, the microstructural evolution and its influence on the mechanical properties of a supersaturated Cu Co solid solution with ~100 nm average grain size prepared by severe plastic deformation is investigated under non-isothermal and isothermal annealing conditions. Pure fine grained Cu and Co exhibit substantial grain growth upon annealing, whereas the Cu Co alloy…
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The thermal decomposition behavior, the microstructural evolution and its influence on the mechanical properties of a supersaturated Cu Co solid solution with ~100 nm average grain size prepared by severe plastic deformation is investigated under non-isothermal and isothermal annealing conditions. Pure fine grained Cu and Co exhibit substantial grain growth upon annealing, whereas the Cu Co alloy is thermally stable at the same annealing temperatures. The annealed microstructures are studied by independent characterization methods, including scanning electron microscopy, electron energy loss spectroscopy and atom probe tomography. The phase separation process in the Cu Co alloy proceeds by the same mechanism, but on different length scales: a fine scaled spinodal type decomposition is observed in the grain interior, simultaneously Co and Cu regions with a larger scale are formed near the grain boundary regions. Subsequent grain growth at higher annealing temperatures results in a microstructure consisting of the pure equilibrium phases. Such mechanisms can be used to tailor nano structures to optimize certain properties.
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Submitted 4 November, 2016;
originally announced November 2016.
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X-Ray Photon Correlation Spectroscopy Reveals Intermittent Aging Dynamics in a Metallic Glass
Authors:
Zach Evenson,
Beatrice Ruta,
Simon Hechler,
Moritz Stolpe,
Eloi Pineda,
Isabella Gallino,
Ralf Busch
Abstract:
We use coherent X-rays to probe the aging dynamics of a metallic glass directly on the atomic level. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is tri…
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We use coherent X-rays to probe the aging dynamics of a metallic glass directly on the atomic level. Contrary to the common assumption of a steady slowing down of the dynamics usually observed in macroscopic studies, we show that the structural relaxation processes underlying aging in this metallic glass are intermittent and highly heterogeneous at the atomic scale. Moreover, physical aging is triggered by cooperative atomic rearrangements, driven by the relaxation of internal stresses. The rich diversity of this behavior reflects a complex energy landscape, giving rise to a unique type of glassy-state dynamics.
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Submitted 2 September, 2015;
originally announced September 2015.