Microscopic evidence of the connection between liquid-liquid transition and dynamical crossover in an ultraviscous metallic glass former

Abstract

Liquid-liquid transitions are interesting to many researchers since they occur in systems 19 as diverse as monoatomic liquids, multicomponent oxides and metallic glass-formers. In 20 some cases, the crossover is accompanied by changes in the dynamical properties, 21 although a direct microscopic evidence of this connection has not been reported so far. 22 By combining state-of-the-art synchrotron techniques, we followed the structure and 23 atomic motion during quasi-static cooling the Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glass-24 former from the low-temperature supercooled liquid. With this thermal protocol, we were 25 able to lower the glass transition temperature far enough to reveal a liquid-liquid 26 crossover between two amorphous structures corresponding to two ultra-viscous liquids 27 with different kinetic behavior. This transition is in competition with vitrification, which 28 occurs at conventional cooling rates, and is accompanied by structural changes not 29 affecting the average density. Our results provide a direct connection between 30 polyamorphism and dynamical crossover, and an alternative case to add in the highly-31 debated topic on the low-temperature divergence of the dynamics in supercooled liquids. 32 33 2Many systems, ranging from monoatomic liquids [1-3] to amorphous alloys [4][5][6][7], exhibit 34 transitions between liquid phases of different local structure. In glass-formers, liquid-liquid 35 transitions (LLTs) have been reported either in high temperature melts [3,[8][9][10][11][12][13] or in 36 supercooled liquids [4][5][6]14,15], suggesting the existence of intrinsic connections between the 37 kinetic properties of the system and the transition temperature [16]. LLTs are sometime 38 associated to a dynamical crossover with changes in the kinetic fragility [6,10,17]. When 39 observed upon cooling, the liquid evolves from a high temperature fragile phase with a steep 40 temperature dependence of viscosity and structural relaxation time, to a strong phase less 41 affected by temperature changes. For fragile liquids, like molecular and some metallic glass-42 formers, the LLT is expected at such a low temperature that the system may arrest beforehand 43 in the glass [16]. Still, no direct microscopic evidence of this and more in general of a direct 44 connection between LLT and dynamical crossover have been reported so far. This is also due 45 to the extreme difficulty of obtaining experimental measurements of the atomic collective 46 motion in glass-formers. 47 By taking advantage of state-of-the-art synchrotron techniques like x-ray photon correlation 48 spectroscopy (XPCS) and high energy x-ray diffraction (XRD), we present the first 49 experimental measurements of the microscopic dynamics of an ultra-viscous glass former with 50 relaxation times which were not accessible until now, neither experimentally nor with 51 numerical simulations. Our data show the occurrence of a LLT upon quasi-static cooling the 52 Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glass-former, which can be direct...

Vitrification decoupling from α-relaxation in a metallic glass

“…The fit of atomic mobility data to the VFT equation delivers T 0 = 348 K, log  0 = − 18, and D* = 6.8 ± 0.2. The latter is characteristic of a fragile liquid (38,47) and is in agreement with the high-temperature liquid fragility for this glass former reported elsewhere (17,43). The temperature dependence of  associated with cooling ratedependent T f values from FSC experiments (star symbols) also exhibits super-Arrhenius behavior but with different parameters.…”

“…S7). (43). Furthermore, characteristic time scales based on previous calorimetric enthalpy recovery studies (17) are reported with diamond symbols.…”

Homogeneous nucleation of phase transformations in supercooled water

“…This crossover has been observed on Vit 1 in 2007, studying the liquid viscosity above Tm and around TBr+ [79]. The crossover at Tg  TBr- Tm has been recently observed in the fragile liquid Au49Cu26.9 Si16.3 Ag5.5 Pd2.3 [80] and cannot be observed in a strong liquid because TBr-= Tg. These crossovers could only occur when glass Phase 3 is formed by previous cooling the melt below Tg and further heating above Tg and Tm.…”

Liquid‐liquid phase transitions in glass‐forming systems and their implications for memory technology

“…4 However, a growing number of systems are found to exhibit abnormal changes in viscosity with temperature as they undergo a transition from fragile to strong (F-S). [5][6][7][8][9][10][11][12][13][14] These transitions are associated with anomalies in multiple thermodynamic variables such as the heat capacity, expansion coefficient and compressibility. 7,15 In some cases the F-S crossover can be extremely sharp, indeed discontinuous, as in the case of Si 16 and models of water.…”