We explained the domain-wall conduction mechanism in multiferroic BiFeO3 with the accumulation of charged defects (Fe4+ ions and Bismuth vacancies) and determined the type of electrical conduction (ptype). The direct determination of charged defects was accomplished using quantitative scanning transmission electron microscopy. In the literature there were no reports on atomic scale quantification of vacancies at domain walls, so we developed original method based on comparison of normalised Bi columns intensities to calculated (simulated) ones where we used multi-slice frozen-phonon approximation. Fe4+ presence was confirmed with EELS spectroscopy at atomic level. Classical Fe L2/L3 EELS edge intensities ratio method was not suitable for the determination of Fe4+ so we used approach based on onset energy difference between O K and Fe L3 edges. Experimental proof of the presence of charged defects (Fe4+ and VBi’’’) at domain walls was a missing piece in BiFeO3 domain walls conductivity mechanism explanation. The work was awarded with the inclusion in the "Excellent in Science in 2017"). By Web of Science (Reuter) this paper was classified as "Higly Cited" paper meaning it is in top 1% of citations in first year for the material science field.
COBISS.SI-ID: 29936679
Based on kinetic Monte Carlo simulation we found that due to ordering of crystal structure and formation of L12 intermetallic compound with a cubic Fm-3m structure the dealloying of catalytic Pt-based particles is substantially lower compared to disordered Pm-3m solid solution. Using Cs-corrected STEM we determined the chemical composition, homogeneity and ordering of the structure of starting and degraded particles after dealloying and provided the experimental proof of calculated results.
COBISS.SI-ID: 5951258
With detailed analysis using transmission electron microscopy it was possible to identify and reconstruct the morphology of individual phases in composite TiO2 nanomaterials consisting of anatase, brookite and rutile crystal phases. Determining the shape and terminal planes of individual nanoparticles we importantly contributed to the explanation of the synthesis and high mineralisation potential of this material.
COBISS.SI-ID: 5753626
Cs corrected scanning transmission electron microscopy enables insight in the crystal structure and chemical composition at atomic level. We studied battery-related material based on LiFePO4 that was prepared with co-precipitation from aqueous media. Direct observation of atomic columns in suitable crystallographic orientation we determined the presence of crystal defects, namelly iron ions at the Li sites inside the olivine LiFePO4 structure. These defects are responsible for the change of unit cell volume which was confirmed also with complementary methods (XRD).
COBISS.SI-ID: 5728026
Study of fluorinated reduced graphene oxide as the interlayer in the Li- S batteries was reported. Part of the research was devoted to the determination of individual fluorine atoms and molecules performed with Cs-corrected STEM. The question we tried to solve was does the fluorine enter the structure of graphene or is just adsorbed as a molecule. Using suitable experimental conditions we were able to collect high-resolution annular dark images of individual fluorine atoms and molecules (pair of atoms at a certain distance). To confirm that the observed features are indeed fluorine atoms we performed image simulations using realistic model and compare the experimental images with calculated ones. Based on intensity and dimension agreement we confirm that part of the fluorine enters the graphene structure and part is tightly adsorbed. Using Electron Energy Loss Spectroscopy (EELS) in low energy (plasmonic) region we determined the number of graphene layers in the examined areas. This approach for differentiating the atoms and molecules of low-Z elements is new and original.
COBISS.SI-ID: 29021479