Miran Čeh

In this work, we systematically investigate the structure of Sr and Mg doped lanthanum gallate single crystals using x-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis revealed the presence of multiple domains with distinct lattice parameters. High-resolution TEM and integrated differential phase contrast imaging captured two regions, one with 90° symmetry and the other with non-90° symmetry. In addition, ordered oxygen vacancies in the non-90° region were revealed, while vacancies in the 90° region were randomly distributed. Energy-dispersive x-ray spectroscopy confirmed that the difference in the doping level of the two regions is within the detectability limits. However, the electron energy loss near-edge structure revealed detectable differences in their bonding character.

In this work, we investigated La0.6Sr0.4CoO3−δ / SrTi0.3Fe0.7O3−δ multilayer systems with different layer thicknesses. Reciprocal space mapping showed splitting of the reflections in the sample with 5 nm layers while for 15 nm thick layers reflections have been elongated. Using transmission electron microscopy, we investigated this phenomenon at the atomic scale and showed that the alternating 15 nm layers gradually increase their tensile out-of-plane strain, whereas the sample with 5 nm layers maintains a relatively stable strain state. In-plane strain relaxation is similar in both samples. Still, it differs in the strain relaxation mechanism, which involves the formation of amorphous regions in the 5 nm sample and the formation of edge dislocations in the 15 nm sample. Electron energy loss spectroscopy was employed to probe the oxidation states of Co, Fe, and Ti. In both samples, the oxygen vacancy concentration increases toward the surface.

The persistent photoconductivity (PPC) effect in nanotube arrays of barium titanate and TiO₂ (BTO/TiO₂NT) was studied at room temperature under daylight illumination. The BTO/TiO₂NT heterostructures exhibited a giant PPC effect that was six orders of magnitude higher than the dark conductivity, followed by a slow relaxation for 3 h. The PPC in this material was explained by the existence of defects at the surfaces and the interfaces of the investigated heterostructures. The sample was prepared using a two-step synthesis: the anodization of a Ti-foil and a subsequent hydrothermal synthesis. The structural and electrical characteristics were studied by micro-Raman spectroscopy, field-emission-gun scanning electron microscopy, and impedance spectroscopy.