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Physical Sciences Applications 09:00 - 12:00 Thursday, 26th November, 2020 Track Physical Sciences Applications Presentation type Oral Presentation 09:00 - 09:15 192 Quantifying ordering phenomena in lanthanum barium ferrate at the atomic scale Judith Lammer1, Christian Berger2, Stefan Löffler3, Daniel Knez1, Paolo Longo4, Edith Bucher2, Gerald Kothleitner1, Andreas Egger2, Rotraut Merkle5, Werner Sitte2, Joachim Maier5, Werner Grogger1 1Institute of Electron Microscopy and Nanoanalysis (FELMI), Graz University of Technology & Graz Centre for Electron Microscopy (ZFE), Graz, Austria. 2Chair of Physical Chemistry, Montanuniversitaet Leoben, Leoben, Austria. 3University Service Centre for Transmission Electron Microscopy (USTEM), TU Wien, Vienna, Austria. 4Gatan Inc., Pleasanton, USA. 5Max Planck Institute for Solid State Research, Stuttgart, Germany Abstract Text Within this abstract we present a high-resolution chemical analysis of the second order Ruddlesden-Popper phase Ba1.1La1.9Fe2O7 using EDX and EELS in STEM, as well as simulations for quantifying the lanthanum and barium concentration on each atom column. Lanthanum barium ferrates have auspicious properties as triple conducting oxides (proton-, oxygen ion- and electron-conducting) and therefore are promising new materials for future applications in protonic ceramic fuel cells, electrolyser cells or membranes for hydrogen separation [1]. However, mass and charge transport as well as defect chemistry are only partially understood at this point. These properties are influenced by the crystal structure and the distribution of the elements within this structure. In this work, we show an element analysis of the second order Ruddlesden-Popper phase Ba1.1La1.9Fe2O7. In addition to characterizing the crystal structure over a large material volume by X-ray diffraction (XRD), we used scanning transmission electron microscopy (STEM) in combination with electron energy loss spectrometry (EELS) and energy-dispersive X-ray spectrometry (EDX) to locally analyse the elemental distribution down to the atomic scale via high-resolution elemental maps. Both La and Ba occupy the A-sites within the crystal. Our experiments show that La favours the 9-fold coordination sites in the rock salt layer, whereas Ba prefers the 12-fold coordination sites within the perovskite block (fig. 1a). Moreover, we recognised fluctuations in the Ba/La distribution on each atom column within both rock salt and perovskite layers (fig. 1b). In order to quantify the EELS spectrum images, one needs to be aware of signal contributions stemming from neighbouring atom columns, which may have serious influence due to the in-zone-axis conditions during data acquisition. Hence we simulated the La and Ba EELS signal using inelastic multislice calculations based on Slater-type orbitals and analysed the contributions coming from either the investigated atom column (on-axis signal) or the neighbouring atom columns (off-axis signal). In doing so, we are able to estimate the off-axis contributions to the experimentally determined signal and therefore quantify the La and Ba concentrations on each atom column. A previous work on the nominal material Ba1La2Fe2O7 shows similar behaviour when it comes to the preferred site of La and Ba in the rock salt and the perovskite layers, respectively [2]. We additionally revealed that (in terms of crystal structure) equivalent atom columns within either the rock salt layer or the perovskite layer do not exhibit distinct La/Ba ratios but a broad variation in concentration. The cation diffusion within the crystallites and the new insights on cation ordering in Ba1.1La1.9Fe2O7 further contribute to the understanding of mass and charge transport properties in order to systematically design new materials for intermediate temperature protonic ceramic fuel cells [3]. Figure 1: a) The EDX elemental map depicts the distribution of La, Ba and Fe in the second order Ruddlesden- Popper phase Ba1.1La1.9Fe2O7 in [100] orientation. b) and c) La and Ba intensity maps evaluated per atom column illustrate the intensity variations on equivalent atom columns. References [1] R Zohourian et al, Advanced Functional Materials 28 (2018), 1801241 [2] NNM Gurusinghe et al, Materials Research Bulletin 48 (2013), p. 3537–3544 [3] The support of the Austrian Research Promotion Agency FFG (No. 853538), the Klima- und Energiefonds within the program "Energieforschung (e!MISSION)", the European Union Horizon 2020 programme (grant 823717–ESTEEM3) and the Austrian Science Fund FWF (No. I4309-N36) is gratefully acknowledged. 09:15 - 09:30 259 Comprehension of gassing mechanism of Ni-rich positive electrode material for lithium-ion batteries through surface analysis by high energy resolution STEM-EELS Angelica Laurita1, Pierre-Etienne Cabelguen2, Liang Zhu2, Dominique Guyomard1, Nicolas Dupré1, Philippe Moreau1 1Université de Nantes, CNRS, Institut des Matériaux Jean Rouxel, IMN, Nantes, France. 2Umicore, Rechargeable Battery Mat, Brussels, Belgium Abstract Text The electrification of vehicles presently relies on lithium ion batteries using layered oxides of nickel, manganese and cobalt (NMC) with high Ni content as positive electrode materials. Nevertheless, it has been demonstrated that these materials suffer from gassing issues decreasing cycle life and causing safety problems [1,2]. Moreover, nickel-rich NMCs are affected by critical instability during all the manufacturing steps (synthesis, handling, electrode preparation). A deep comprehension of the pristine material properties and of its behaviour during electrode preparation and electrochemical cycling is thus fundamental from the industries’ point of view. In this context a systematic study of the surface reactivity of NMC811 (Li[Ni0.8Mn0.1Co0.1]O2) was conducted using a multi-analytical approach in which transmission electron microscopy plays an essential role. A new TEM/STEM Themis Z G3 (Thermo Fisher Scientific) equipped with a double camera GIF spectrometer, was, in fact, recently installed in the Jean Rouxel Institute of Materials of Nantes (France). Electron Energy Loss Spectroscopy (EELS) was in particular exploited in order to give a complete description of the surface of the material. The direct detection camera (Gatan K2 Summit) allowed the acquisition of EELS spectra in STEM mode with both high energy and spatial resolution. This enables a good multi-elemental chemistry mapping quantification (at low energy dispersions) as well as the accurate analysis of the fine structures of the Ni L23 -edges thanks to the use of an excited monochromator. Moreover, the use of a vacuum transfer sample holder insured the observation of samples without any contact with the ambient atmosphere. The samples were in fact transferred directly to the microscope from the Argon glove box where they were stored, preventing any sort of reaction of the material with air and thus allowing the proper analysis of the material in its initial state. In this way it was possible to look at the surface modifications and to compare them to the bulk structure by means of the multiple linear least square (MLLS) fitting; the thickness of the surface modified layer was then determined for all the samples, proving the high reactivity of the material surface in the ambient atmosphere. The Ni L3-edge changes in fact between the surface and the bulk of the material, indicating its oxidation state’s evolution after 5 days of exposition in air. The reduced Ni was found for about the first 15 nm of the surface. Correspondingly, the disappearance of the oxygen pre-edge was observed. On the other hand, the analysis of the same powder transferred directly from the glove box revealed a similar behaviour of the Ni L-edge (Figure 1) in the first 6 nm of surface only; a slight change in the shape of the oxygen K-pre-edge was also observed, indicating that a gradual but not yet completed evolution of the material surface. Figure 1: Evolution of Ni L-edge in the pristine NMC 811 powder Similarly, the calculation of the ratio between the Ni L3/L2-edges was performed on the entire EELS spectrum image allowing the valence mapping of the material after the comparison with proper references. Moreover, through the calculation of the second derivative of the EELS spectra, a quantification of all the transition metals was performed. In fact, it has to be considered that the small quantity of Mn and Co in the material doesn’t usually allow the correct quantification of these species, since the corresponding intensity signal is too low and often confused into the background. For this reason, changes in the surface composition of this materials have rarely been deduced by EELS spectra at this level of precision. In addition to primary particle analysed above, FIB lamella were also produced on secondary particles (made of these primary particles) actually used by our industrial partner. First results on these closer to application samples will be presented so that we can demonstrate how the observed phenomena on primary particles translate at a larger scale. To conclude, EELS Spectrum Images were analysed in order to obtain qualitative and quantitative information about the surface of NMC811, essential to the good comprehension of its reactivity and gassing behaviour. EELS was used for the determination of both the valence state, coordination and quantity of all the transition metals as well as for the qualitative identification of surface modifications in particular aging conditions. References [1] Berkes, B. B. et

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