Chrisitan KÜBEL

INSTITUTE OF NANOTECHNOLOGY - INT (Karlsruhe)

Chrisitan KÜBEL

INSTITUTE OF NANOTECHNOLOGY - INT (Karlsruhe)

Résumé

Imaging the Radial Distribution Function in Complex Glasses using Scanning Diffraction Techniques

Xiaoke Mu1,2, Di Wang1,3, Ali Ahmedian1 and Christian Kübel1,2,3

1. Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
2. Helmholtz-Institute Ulm for Electrochemical Energy Storage (HIU), Karlsruhe Institute of Technology (KIT), 89081 Ulm, Germany
3. Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany

Scanning diffraction imaging (4D-STEM) techniques have seen an impressive development with automated crystal orientation mapping (ACOM) [1] opening the door to a variety of related approaches enabling a quantitative metallographic analysis [2], local strain measurements [3], or a description of the disordered structure in glasses [4] at the nanoscale. The combination of large area imaging with high spatial resolution and quantifiable information is providing unprecedented information to understand the structure and properties of materials. Furthermore, these techniques are suitable for in situ investigations to follow dynamic processes [2, 5].

In the present work, we are focusing on understanding the local structure in complex glasses. Only few experimental means offer a way to characterize these disordered structures. The atomic radial distribution function (RDF) is one of the important tools, which was first developed for X-ray diffraction and afterwards extended to selected area electron diffraction for inorganic glasses [6]. The RDF describes the probability to find certain atomic pairs as a function of the pair separation and, consequently, provides short and medium range structural information. For a local analysis, RDF imaging, we are combining quasi parallel nano-beam electron diffraction in micro-pSTEM with RDF analysis [4]. The RDFs are calculated from all diffraction patterns to construct a 3D data cube of RDFs. The data cube can be analyzed by hyperspectral techniques to obtain phase maps for the different amorphous materials (Fig. 1). Compared to fluctuation electron microscopy, RDF imaging has the advantage that the RDF of each phase can be analyzed in terms of bond distance, bond angle and coordination number to get direct structural information in addition to the phase distribution.

We have been applying RDF imaging to a variety of different materials and will illustrate the technique and the information that can be obtained by looking at multilayered metallic glasses, structural variations in shear bands as well as bulk metallic glasses and the structure of nano glasses. Furthermore, it is also possible to apply this approach to a combination of crystalline and amorphous materials.

References:

[1] E.F. Rauch et al., Zeitschrift für Kristallographie, 2010, 225, p. 103.
[2] J. Lohmiller et al., Acta Materialia, 2014, 65, p. 295.
[3] C. Gammer et al, Ultramicroscopy 2015, 155, p. 1.
[4] X. Mu et al., Ultramicroscopy, 2016, 168, p. 1.
[5] A. Kobler et al., Ultramicroscopy, 2013, 128, p. 68.
[6] D.J.H Cockayne, D.R. Mckenzie, Acta Crystallographica Section A, 1988, 44, p. 870.

fig_kuebel

Figure 1. Sketch of procedures to calculate the RDF-cube from experimental STEM-diffraction data and MLLS analysis of the RDF-cube. (a) HAADF image. (b) A typical diffraction pattern in STEM-diffraction. (c) Annular averaged diffraction profile. (d) Structure factor. (e) RDF obtained by Fourier transform of structure factor. (f) Reference RDFs. (g) Sketch of the constructed RDF data cube (RDF-Cube). (h) Imaging results: structural maps.

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