Limits...
Five-fold symmetry as indicator of dynamic arrest in metallic glass-forming liquids.

Hu YC, Li FX, Li MZ, Bai HY, Wang WH - Nat Commun (2015)

Bottom Line: Here, we report that a universal structural indicator, the average degree of five-fold local symmetry, can well describe the slowdown dynamics during glass transition.A straightforward relationship between structural parameter and viscosity (or α-relaxation time) is introduced to connect the dynamic arrest and the underlying structural evolution.This finding would be helpful in understanding the long-standing challenges of glass transition mechanism in the structural perspective.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physics, Chinese Academy of Sciences, Beijing 100190 China.

ABSTRACT
With sufficient high cooling rates, a variety of liquids, including metallic melts, will cross a glass transition temperature and solidify into glass accompanying a marked increase of the shear viscosity in approximately 17 orders of magnitude. Because of the intricate atomic structure and dynamic behaviours of liquid, it is yet difficult to capture the underlying structural mechanism responsible for the marked slowing down during glass transition, which impedes deep understanding of the formation and nature of glasses. Here, we report that a universal structural indicator, the average degree of five-fold local symmetry, can well describe the slowdown dynamics during glass transition. A straightforward relationship between structural parameter and viscosity (or α-relaxation time) is introduced to connect the dynamic arrest and the underlying structural evolution. This finding would be helpful in understanding the long-standing challenges of glass transition mechanism in the structural perspective.

No MeSH data available.


Related in: MedlinePlus

Correlation between structure parameter W and atomic mobility.(a) Distribution of atomic mobility at T=1.2Tg in different systems. There is a long tail in the distribution for all the simulated systems, which can be fitted by a stretched exponential function  with 0<β<1 (green solid lines), indicating heterogeneous dynamics. (b) The dependence of atomic mobility on W in various simulated systems (the same colour in a,b represents the same system).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4595736&req=5

f4: Correlation between structure parameter W and atomic mobility.(a) Distribution of atomic mobility at T=1.2Tg in different systems. There is a long tail in the distribution for all the simulated systems, which can be fitted by a stretched exponential function with 0<β<1 (green solid lines), indicating heterogeneous dynamics. (b) The dependence of atomic mobility on W in various simulated systems (the same colour in a,b represents the same system).

Mentions: The atomic mobility can reflect the effect of local structure on the dynamical behaviour of atoms. The non-Gaussian parameter (ref. 34), , is commonly believed to reflect dynamical heterogeneity in supercooled liquids. The peak time t* in represents the timescale at which the distribution of atomic motion is the most heterogeneous22. The atomic mobility of atom i can then be evaluated in the time interval of t=t* according to for various MG-forming liquids. Figure 4a shows the distribution of atomic mobility in the investigated systems at T=1.2Tg. It is clear that the distributions of atomic mobility with very long tails significantly deviate from Gaussian distribution, indicating the inhomogeneous dynamics in the supercooled MG-forming liquids, which is in agreement with previous results22363738. Furthermore, the long tails in the distribution can be well fitted with a stretched exponential function , as shown in Fig. 4a. The parameter β was fitted to be about 0.77, 0.86, 0.81, 0.84, 0.82, 0.75, 0.83 and 0.83 for Cu46Zr46Al8, Zr45Cu45Ag10, Cu50Zr50, Ni80P20, Pd82Si18, Mg65Cu25Y10, Ni33Zr67 and Ni50Al50, respectively. These values are all smaller than 1, further indicating the heterogeneous dynamics in all the supercooled MG-forming liquids37. In the following, we will establish a link between atomic mobility and the five-fold local symmetry.


Five-fold symmetry as indicator of dynamic arrest in metallic glass-forming liquids.

Hu YC, Li FX, Li MZ, Bai HY, Wang WH - Nat Commun (2015)

Correlation between structure parameter W and atomic mobility.(a) Distribution of atomic mobility at T=1.2Tg in different systems. There is a long tail in the distribution for all the simulated systems, which can be fitted by a stretched exponential function  with 0<β<1 (green solid lines), indicating heterogeneous dynamics. (b) The dependence of atomic mobility on W in various simulated systems (the same colour in a,b represents the same system).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595736&req=5

f4: Correlation between structure parameter W and atomic mobility.(a) Distribution of atomic mobility at T=1.2Tg in different systems. There is a long tail in the distribution for all the simulated systems, which can be fitted by a stretched exponential function with 0<β<1 (green solid lines), indicating heterogeneous dynamics. (b) The dependence of atomic mobility on W in various simulated systems (the same colour in a,b represents the same system).
Mentions: The atomic mobility can reflect the effect of local structure on the dynamical behaviour of atoms. The non-Gaussian parameter (ref. 34), , is commonly believed to reflect dynamical heterogeneity in supercooled liquids. The peak time t* in represents the timescale at which the distribution of atomic motion is the most heterogeneous22. The atomic mobility of atom i can then be evaluated in the time interval of t=t* according to for various MG-forming liquids. Figure 4a shows the distribution of atomic mobility in the investigated systems at T=1.2Tg. It is clear that the distributions of atomic mobility with very long tails significantly deviate from Gaussian distribution, indicating the inhomogeneous dynamics in the supercooled MG-forming liquids, which is in agreement with previous results22363738. Furthermore, the long tails in the distribution can be well fitted with a stretched exponential function , as shown in Fig. 4a. The parameter β was fitted to be about 0.77, 0.86, 0.81, 0.84, 0.82, 0.75, 0.83 and 0.83 for Cu46Zr46Al8, Zr45Cu45Ag10, Cu50Zr50, Ni80P20, Pd82Si18, Mg65Cu25Y10, Ni33Zr67 and Ni50Al50, respectively. These values are all smaller than 1, further indicating the heterogeneous dynamics in all the supercooled MG-forming liquids37. In the following, we will establish a link between atomic mobility and the five-fold local symmetry.

Bottom Line: Here, we report that a universal structural indicator, the average degree of five-fold local symmetry, can well describe the slowdown dynamics during glass transition.A straightforward relationship between structural parameter and viscosity (or α-relaxation time) is introduced to connect the dynamic arrest and the underlying structural evolution.This finding would be helpful in understanding the long-standing challenges of glass transition mechanism in the structural perspective.

View Article: PubMed Central - PubMed

Affiliation: Institute of Physics, Chinese Academy of Sciences, Beijing 100190 China.

ABSTRACT
With sufficient high cooling rates, a variety of liquids, including metallic melts, will cross a glass transition temperature and solidify into glass accompanying a marked increase of the shear viscosity in approximately 17 orders of magnitude. Because of the intricate atomic structure and dynamic behaviours of liquid, it is yet difficult to capture the underlying structural mechanism responsible for the marked slowing down during glass transition, which impedes deep understanding of the formation and nature of glasses. Here, we report that a universal structural indicator, the average degree of five-fold local symmetry, can well describe the slowdown dynamics during glass transition. A straightforward relationship between structural parameter and viscosity (or α-relaxation time) is introduced to connect the dynamic arrest and the underlying structural evolution. This finding would be helpful in understanding the long-standing challenges of glass transition mechanism in the structural perspective.

No MeSH data available.


Related in: MedlinePlus