Disentangling structural and kinetic components of the α-relaxation in supercooled metallic liquids

Abstract

The particle motion associated to the α-relaxation in supercooled liquids is still challenging scientists due to its difficulty to be probed experimentally. By combining synchrotron techniques, we report the existence of microscopic structure-dynamics relationships in Pt42.5Cu27Ni9.5P21 and Pd42.5Cu27Ni9.5P21 liquids which allows us to disentangle structural and kinetic contributions to the α-process. While the two alloys show similar kinetic fragilities, their structural fragilities differ and correlate with the temperature dependence of the stretching parameter describing the decay of the density fluctuations. This implies that the evolution of dynamical heterogeneities in supercooled alloys is determined by the rigidity of the melt structure. We find also that the atomic motion not only reflects the topological order but also the chemical short-range order, which can lead to a surprising slowdown of the α-process at the mesoscopic length scale. These results will contribute to the comprehension of the glass transition, which is still missing.

Pressure-induced nonmonotonic cross-over of steady relaxation dynamics in a metallic glass

“…Moreover, the origin of compressed decay ( β > 1) is proposed to be structural, e.g., microscopic collapse ( 47 , 48 ), long-range microscopic spatial correlations ( 49 ), clustering of icosahedra ( 24 ), or elastic frustration ( 50 ) in many hard or soft materials. In this work, β remains constant within error bars, suggesting its independence from changes in the SRO and density of a glass and also agrees with recent results on other MGs at the glass transition ( 43 ). In contrast, another parameter, c , is found to couple with glass structures.…”

“…For example, the characteristic atomic cluster in Cu 64 Zr 36 MG is full icosahedra (Voronoi index <0, 0, 12, 0>) ( 41 ), but in Mg 65 Cu 25 Y 10 MG, bicapped square antiprisms (<0, 2, 8, 0>) and tricapped trigonal prisms (<0, 3, 6, 0>) are dominant clusters ( 42 ). Evidence of a strict relation between local atomic structures and collective motion has been recently reported for a supercooled metallic liquid ( 43 ).…”

“…The electronic structure transition is directly coupled with the atomic rearrangement during the polyamorphic transition. During the polyamorphic transition, a double-well feature emerges in the Ce–Ce interatomic potential with a relatively small barrier between the two potential wells, which replaces the regular single-well potential ( 38 , 39 ). According to a recent simulation work dealing with pressure-induced structural rejuvenation ( 44 ), this emerging two-state feature in potential could lead to structural rejuvenation and therefore accelerated relaxation dynamics.…”

Molecular dynamics investigation of benzoic acid in confined spaces

“…It is difficult to attach a clear physical meaning to such figures, as testified by the rich and ongoing debate on the application of the KWW function to relaxation phenomena in liquids and glasses. 48,49,51–53 However, it is worth noting our β ⊥ estimates lie around β SR = 3/5 = 0.6, which is the value expected for relaxation dynamics slowed down by short-range forces in three-dimensional spaces. 48 Likely, this further points out the pivotal role of short hydrogen bonds in determining the dynamics of the liquid at the molecular scale.…”

“…In this case, a threshold distance equal to 0.9 times the sum of van der Waals radii was used to exclude long, weak contacts (Section S6, ESI †). 53 This definition is rather conservative, as the same HB interaction may be destroyed and formed several times along the trajectory; however, it has the advantage of getting rid of ambiguities due to intermittent contacts. If the HÁ Á ÁO contacts that fulfil this geometric requirement are counted, the average number of HBs per frame amounts to B433 (Fig.…”