Abstract
Preparation history and processing have a crucial influence on which configurational state material systems assume. Glasses and nanocrystalline materials usually reside in nonequilibrium states at room temperature, and as a consequence, their thermodynamic, dynamical, and physical properties change with time—even years after manufacture. Such changes, entitled aging or structural relaxation, are all manifestations of paths taken in the underlying potential energy landscape. Since it is highly multidimensional, there is a need to reduce complexity. Here, we demonstrate how to construct a one-dimensional pathway across the energy landscape using strain/volume as an order parameter. On its way to equilibrium, we map the system’s release of energy by calorimetry and the spectrum of barrier heights by dilatometry. The potential energy of the system is reduced by approximately kBT during relaxation, whereas the crossing of saddle points requires activation energies in the order of 1eV/atom relative to the energy minima. As a consequence, the system behaves as a bad global minimum finder. We also discovered that aging is accompanied by a decrease in the non-ergodicity parameter, suggesting a decline in density fluctuations during aging.
Highlights
It is widely recognized that disordered solids, such as amorphous or nanostructured materials, are not in equilibrium relative to a laboratory time scale
Glasses and nanocrystalline materials usually reside in nonequilibrium states at room temperature, and as a consequence, their thermodynamic, dynamical, and physical properties change with time—even years after manufacture
Their thermodynamic, dynamic, and physical properties change with time—even years after the time of manufacture. This change in properties with time far from equilibrium is termed aging or structural relaxation.[1,2]. The latter term suggests that the underlying microscopic processes cause configurational rearrangements in the system, which result in changes in state variables as well as physical properties.[2]
Summary
It is widely recognized that disordered solids, such as amorphous or nanostructured materials, are not in equilibrium relative to a laboratory time scale. This change in properties with time far from equilibrium is termed aging or structural relaxation.[1,2] The latter term suggests that the underlying microscopic processes cause configurational rearrangements in the system, which result in changes in state variables (e.g., volume, enthalpy) as well as physical properties.[2] It is well established that both kinetic and thermodynamic properties of a system depend on its potential energy Φ,3,4 which is a function of the configuration of the system It is characterized by the positions of all N constituting particles (atoms, molecules, etc.), represented by N independent position vectors ~r1, . The rugged character of such hypersurfaces inspired the potential energy landscape (PEL) paradigm to emphasize the relevance of the topographic features of these hypersurfaces, that is, inherent structures, basins, saddle points, and metabasins.[5,6]
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