Structural, dynamic, electronic, and vibrational properties of flexible, intermediate, and stressed rigid As-Se glasses and liquids from first principles molecular dynamics

Abstract

The structural, vibrational, electronic, and dynamic properties of amorphous and liquid AsxSe1-x (0.10 <x < 0.45) are studied by First Principles Molecular Dynamics. Within the above range of compositions, thresholds, and anomalies are found in the behavior of reciprocal and real space properties that can be correlated to the experimental location of the Boolchand intermediate phase in these glassy networks, observed at 0.27 <x < 0.37. These findings are associated with diffusion anomalies for the parent liquid phase, thereby linking structural and dynamical atomic-scale fingerprints for the onset of rigidity within the network, while also providing a much more complex picture than the one derived from mean-field approaches of stiffness transitions.

Relaxation and physical aging in network glasses: a review

“…42, right) for the diffusivity [71,290,301,378,379,382] leading to an estimate of an activation energy E A (e.g. Fig.…”

“…A slightly different situation occurs in glasses subject to stress, i.e. densified silicates [279] or stoichiometric chalcogenides [71,287] which exhibit an increased angular bending motion of tetrahedra, as discussed below. [310].…”

“…The correlation with chemical order is also debated by Boolchand and others who have emphasized the link between fragility minima and Figure 6. Correlation between relaxation properties, calculated diffusivity D (blue) and activation energy E A for diffusivity (red axis of the upper panels), and structural properties in the glassy state (black curve, width ∆k F SDP of the FSDP) in systems with changing pressure (2SiO 2 -Na 2 O, [69,70], left panels) or changing composition (As-Se, [71], right panels). Note that for As-Se, an opposite behavior for ∆k F SDP with composition is found from Reverse Monte Carlo [72].…”

“…By analyzing the typical features of the simulated structure factors with changing thermodynamic conditions (density, composition), Bauchy and Micoulaut [69,70,71] have found that anomalies (extrema) in properties associated with glassy dynamics (diffusivity D, activation energy E A which is proportional to fragility if T g does not vary too much) are correlated with anomalies in structural features, as revealed by the change in FSDP (peak position k F SDP and width ∆k F SDP , Fig. 6).…”

“…A set of NDFs can be defined by fixing the neighbor number n (first, second etc) during bond lifetime, the sum of all NDFs yielding the usual i-centred pair correlation function g i (r) whose integration up to the first minimum gives the coordination numbers r i , and hence the corresponding number of bond-stretching constraints r i /2 [71,294,309,310,311]. Figure 28 shows an application to amorphous As 2 Se 3 [71]. In As 2 Se 3 , three NDFs (colored curves) contribute to the first peak of the As-centred pair correlation function g As (r), very well separated from the second shell of neighbours, and indicative of the presence of three neighbours around an As atom.…”