Coincidence of collective relaxation anomaly and specific heat peak in a bulk metallic glass-forming liquid

Abstract

The study of relaxational behavior of multi-component metallic liquids still holds the key to understanding and improving the glass-forming abilities of bulk metallic glasses. Herein, we report measurements of the collective relaxation times in a melted bulk metallic glass (LM601 Zr51Cu36Ni4Al9) in the kinetic regime (Q: 1.5 -4.0Å−1 ) using Quasi-Elastic Neutron Scattering (QENS). The results reveal an unusual slope change in the Angell plots of the collective relaxation time of this metallic liquid around 950• C, beyond the melting point of the material. Specific heat capacity measurement also reveals the presence of a peak around the same temperature. The coincidence is rationalized using Adams-Gibbs theory, and motivates more careful experimental and computational studies of the metallic liquids in the future.

Onset of Cooperative Dynamics in an Equilibrium Glass-Forming Metallic Liquid

“…Fourier transform of the Kohlrausch−Williams−Watts (KWW) stretched exponential function convoluted with the instrumental energy resolution function eq 1 provides excellent fit to the QENS spectrum. 34,43…”

“…At high temperatures, the detailed balance factor is negligible in the measured dynamic range. Fourier transform of the Kohlrausch–Williams–Watts (KWW) stretched exponential function convoluted with the instrumental energy resolution function eq provides excellent fit to the QENS spectrum. , where N is the normalization prefactor; f ( Q ) is the fraction of elastic scattering component that takes into account any contribution from immobile particles with very low mobility such that they appear immobile in the measured QENS time window, and remnant elastic background; F ( Q , t ) is the intermediate scattering function that quantifies both the self-and collective density correlations because of their similar time scale in the studied Q range; and R ( Q , E ) is the Q -dependent instrumental energy resolution function. The density correlator F ( Q , t ) is modeled as where A Q is the effective Debye–Waller factor in a liquid, τ is the relaxation time, and β is the stretching exponent.…”

“…The samples were cast into rectangular slabs with dimensions of 30 mm ×30 mm ×2.5 mm and bulk density of 6.8 g/cm 3 . The material undergoes a glass transition at 697 K and extends up to 730 K, with complete melting observed at 1170 K as revealed by the Differential Scanning Calorimetric (DSC) measurements reported elsewhere …”

“…The material undergoes a glass transition at 697 K and extends up to 730 K, with complete melting observed at 1170 K as revealed by the Differential Scanning Calorimetric (DSC) measurements reported elsewhere. 34 Quasi-Elastic Neutron Scattering (QENS). QENS measurements were carried out at the Cold Neutron Chopper Spectrometer (CNCS) at the Spallation Neutron Source at Oak Ridge National Laboratory.…”

“…It remains an open question whether such a crossover happening at twice of T g in metallic liquids, unlike many molecular systems, has a thermodynamic origin. 34 A fundamental link between the kinetic fragility and the onset temperature in glass-forming liquids remains unexplored. Furthermore, the observation of dynamic crossover in both diffusion coefficient and the viscosity of metallic liquids tied with the breakdown of Stokes−Einstein relation in metallic liquids is an intriguing question that we are exploring.…”