Michal Pilch

Electroreduction in YSZ progresses through three main stages: reversible blackening; accelerated formation of a mixed ionic-electronic pathway; and a runaway process causing the formation of filamentary structures in the surface region.

A series of ZnCr_2−xHo_xSe₄ microcrystalline spinels (where x = 0.05, 0.075, and 0.10) containing holmium ions in octahedral coordination were obtained by sintering of adequate reactants at high temperatures. The obtained doped materials were characterized by X-ray diffraction, Scanning Electron Microscopy, UV–Vis–NIR, molecular field approximation, and XPS spectroscopies. Their thermal properties were also investigated. The doping of the ZnCr₂S₄ matrix with paramagnetic Ho³⁺ ions with a content of not more than 0.1 and a screened 4f shell revealed a significant effect of orbital and Landau diamagnetism, a strong reduction in short-range ferromagnetic interactions, and a broadening and shift of the peak of the first critical field by simultaneous stabilization of the sharp peak in the second critical field. These results correlate well with FPLO calculations, which show that Cr sites have magnetic moments of 3.19 µ_B and Ho sites have significantly larger ones with a value of 3.95 µ_B. Zn has a negligible magnetic polarization of 0.02 µ_B, and Se induces a polarization of approximately −0.12 µ_B.

Our paper is focused on the investigation of the dopant distribution in lanthanum-doped strontium titanate (LSTO) single crystals with a 5 wt.% doping level of La. Using X-ray diffraction analysis and pycnometric density measurement, we have found a discrepancy between the theoretical density and the experimentally determined value. The origin of this behavior could be either the creation of the voids in the matrix or the intergrowth of secondary phases with La surplus in the crystal. Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and selected area diffraction (SAD) microscopic investigation have confirmed the second hypothesis, namely, that in different regions of LSTO, the local concentration of La shows a substantial variation on the micro- and nanoscopic scale. In order to study the influence of the La dopants on the electronic structure and, therefore, on the electrical conductivity, we have used the local conductivity atomic force microscopy (LCAFM) method as a local electrical probe to map the in-plane electrical conductivity of the La-doped crystal’s surface. The LCAFM conductivity maps reveal heterogeneous conductivity (here in the form of the bands with higher conductivity than the surroundings), related to band-like inhomogeneities of the La distribution. Using LCAFM measurements with atomic resolution obtained between the conducting and nonconducting regions, we analyzed the spreading (spatial expansion) of doping on the undoped or low-doped part of the STO crystal. The found limitation of the doping effect of La on the dielectric part of the STO crystal to 4–5 lattice constants was in good correlation with ab initio studies from the literature.

We study the so-called self-polarization phenomenon in single, electroded PbTiO₃ crystals. In this case, near the electrodes, surface layers are formed with a chemically modified perovskite structure. This generates a built-in electric polarization, which cannot be switched permanently by an external electric field. While the initial samples, having two such surface layers with opposite directions of built-in polarization, exhibit ordinary symmetric hysteresis loops, the “asymmetric” samples, with one of these surface layers removed, show asymmetric hysteresis loops. To describe our experimental findings, we combine two kinds of models: one is phenomenological, utilizing the above general features; and the other is ab initio, taking into account the actual atomic structure at the bulk ferroelectric–surface layer–electrode interface. Namely, the ab initio calculations show that the electric polarization within the surface layer occurs due to the shifts of the relaxed Ti ions with respect to the oxygen ion octahedra on the PbO-terminated surface. We ascribe the self-polarization effect to the occurrence of the built-in electric field resulting from the formation of Pb-O planes within the surface layer.

Molybdenum disulfide (MoS₂) was supported on graphene oxide (GO) by hydrothermal method. The resulting nanocomposite (MoS₂-rGO) was characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The experiments show that at pH 2, MoS₂-rGO has a great affinity for adsorption of hexavalent chromium ions while Cr(III) ions remain in aqueous sample. In the adsorption process, the dominant role plays chemisorption. The determined adsorption capacity is 583.5 mg g⁻¹. Parameters affecting the extraction process, namely sample pH, sample volume, contact time, and matrix ions, were investigated by sequential batch tests. Under optimal conditions (pH 2, sample volume 50 mL, sonication time 10 min, adsorbent mass 1 mg), the calibration curve covers the 1–200 ng mL⁻¹ range with a correlation coefficient (R²) of 0.998. The recovery of the method is 97 ± 3%. Other data of merit include a relative standard deviation of < 3.5%, enrichment factor of 3350, and detection limit of 0.050 ng mL⁻¹. The accuracy of the method was confirmed by analysis of the reference materials QC1453 (chromium VI in drinking water) and QC3015 (chromium VI in seawater). The method was successfully applied to chromium speciation in water samples, including high salinity ones. The concentration of Cr(III) was calculated as the difference between the total concentration of chromium (after oxidation of Cr(III) to Cr(VI) with potassium permanganate) and the initial Cr(VI) content.Graphical abstract

The paper presents mechanical properties of the porous Ti scaffold made with saccharose as a space holder. The Ti scaffolds had the porosity of 50, 60 and 70% and were made using 100 and 325 mesh Ti as a scaffold material. The pores were established using saccharose spherical space holder particles of 0.7–0.9 mm in diameter. The local mechanical properties of the Ti scaffold have been measured using nanoindenter. Several loading-unloading characteristics of the thin scaffold walls in the microscale have been measured. It has been observed that Ti scaffolds have very high mechanical properties measured in the microscale that are correlated with partial scaffold oxidation and a formation of TiO₂, which took place during the production stages. The scaffold is composed mainly of Ti oxide and the structure has been identified by XRD as well as XPS. The highest mechanical properties have scaffolds composed of 100 mesh Ti particles, compared to 325 mesh Ti. The microscale tests measurements are rather slightly affected by the pore presence and are under influence of Ti particles. The MTT test shows slightly higher proliferation of NHost cells on porous Ti scaffold in comparison to the reference Ti sample.