Research Digest 19We select Zr50Cu40Al10 metallic glass as a sample. The glass transition temperature of this sample is 673 K. We heat up the sample at 633 ~ 673 K by using in-situ heating holder and conduct 5D-STEM observation. We assess the dynamic from the temporal series of diffraction via time decay of the correlation of diffraction patterns. We also assess the local order of structure via the intensity deviation of the diffraction patterns. This value become high when the diffraction has sharp spot. Thus, if the structure has some orders, this value becomes high. In figure 1, we show the spatial distribution of relaxation times and local order. As you can see, both spatial distributions are heterogeneous. We measured the correlation between these heterogeneities by Spearman’s rank correlation. The value was 0.39. The positive correlation indicate that the highly ordered region tends to have slow dynamics. We also measured temperature dependence of the relaxation time, the local order, and correlation. As a result, the relaxation time decrease and correlation decrease as temperature local order decreases as temperature increase. These results indicate that the local motion become higher as temperature increases and the structure becomes random as temperature increases. These results agree with previous research. In this research, we visualized the spatial distributions of relaxation times and orders at nanoscale by using 5D-STEM method. We found the positive correlation between relaxation times and orders which indicates ordered structures have slow dynamics.Fig. 1. Spatial distributions of relaxation times (upper half) and local orders (lower half) and their temperature dependence. Cite from 2) References 1) K. Nakazawa et al., Microscopy, 72, 5, 446-449 (2023) 2) K. Nakazawa et al., arXiv., arXiv:2305.06521 (2023)the increase, and 1. Outline of ResearchThe glass transition is a phenomenon in which disordered motions of atoms and molecules at high temperatures are quickly cooled down and frozen without crystallization, leaving the disordered structure of atoms and molecules. The freezing of the motion progresses rapidly within a temperature range of a few Kelvins near the glass transition temperature, and the viscosity increases by more than ten orders of magnitude. Simulations revealed that there are heterogeneous regions in the speed of atomic motion near the glass transition temperature. This heterogeneity of atomic motion is called dynamic heterogeneity. Since the correlation length of the dynamical heterogeneity shows critical phenomenon-like behavior near the glass transition temperature, it is predicted that the dynamical heterogeneity plays an important role in glass transition. It is also indicated by simulation that there is a relationship between dynamic heterogeneity and the heterogeneity in atomic structure (structural heterogeneity). However, the relationship has not been confirmed experimentally. This is because it is difficult to observe structural and dynamic heterogeneities during the transition from the liquid state to the glassy state at nano-level resolution. In this study, I focus on convergent beam electron diffraction (CBED) which has a nano-level spatial resolution. Because CBED can analyze a local atomic structure. Thus, spatial series of CBED can visualize the structural heterogeneity. In addition, the temporal series of CBED can measure an intensity of a motion of the local atomic structure. Thus, the spatiotemporal series of CBED can visualize the dynamic heterogeneity. The spatiotemporal series of CBED can measure both heterogeneities, simultaneously. We developed this method to obtain the spatiotemporal distribution of diffraction patterns and call the method as 5D-STEM1. 2. Research ActivitiesMeasurement of Dynamic Heterogeneity Near The Glass Transition Temperature Using Advanced Transmission Electron MicroscopyKatsuaki NAKAZAWA
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