Immanuel Kant Baltic Federal University

We studied the effect of the duration of hydrothermal synthesis in the range from 8 to 12 h on the formation of the structural and magnetic properties of cobalt ferrite CoFe2O4 nanoparticles obtained in the presence of sodium dodecyl sulfate. It was shown that there is a transition from a unimodal particle distribution to a pronounced bimodal one, as well as an increase in crystallite sizes, microstrains, coercive force, and magnetic dipole–dipole interactions.

In the present paper, we study the relationship between the order statistics by using the Kendall correlation coefficient. We show that this relationship is positive and decreases as the distance between indices of order statistics increases for a fixed sample size. We also compare the values of the Kendall correlation coefficient for order statistics with the corresponding values of the Pearson correlation coefficient. We conduct simulation experiments, and these experiments sustain our theoretical results and show that the Kendall correlation coefficient of order statistics has better precision than the Pearson correlation coefficient.

We address a possible development of a semiotic theory based on the principle of asymmetric dualism proposed by S. Kartsevsky. We identify its differences from the Saussurean view of sign and demonstrate that, while Kartsevsky adopts the principle of differentiation, he supplements it with a dynamic understanding of intrasystem relations. This makes it possible to construct multidimensional semiotic models describing how new meanings are generated due to the sign’s asymmetric dualism. We consider the semantics of linguistic sign as a structure in the state of dynamic equilibrium. Thus, we clarify Kartsevsky’s concept of transposition, supplementing it with a concept of disposition (situation of the initial semiosis).

The synthesis of protective cobalt-manganese spinel coatings was accomplished through the utilization of the non-stationary electrolysis method, applied to the surface of Crofer 22 APU stainless steel. In order to achieve optimal electrical conductivity and enhanced stability of the phase composition within the cathode chamber of the SOFC, the Co-Mn spinel coatings were doped with copper, nickel, or iron. XRD analysis indicates that the primary phase is manganese-cobalt spinel (MnCo2O4). As indicated by the XPS data, cobalt exhibits a charge state of 2+, while manganese displays a charge state of 2+ and 4+. Iron is predominantly oxidized to the 2+ state. Nickel, copper, and cobalt all demonstrate a charge state of 2+. It was established that ASR for Cu-, Ni-, and Fe-doped protective cobalt-manganese spinel coatings exhibited sufficiently low resistance values of 5-20 m Omega cm2 after 2500 h of oxidation in air in contact with the LSM cathode at a constant current load of 0.5 A/cm2.

Bismuth ferrite (BiFeO3, BFO) is one of the most prominent multiferroic materials due to the coexistence of ferroelectric and magnetic orders at room temperature. However, its practical implementation is hindered by high leakage currents and limited resistivity. This review critically evaluates recent advances in the synthesis and doping of BFO across various structures-particularly thin films (TFs), nanoparticles (NPs), and ceramics (Ccs)-to enhance their structural, magnetic, and electrical properties. A central focus is on chemical substitution strategies at both A- and B-sites, enabling tailored modifications in crystallographic symmetry, magnetic order, and ferroelectric behavior. The analysis encompasses over 140 doped systems, revealing trends in site occupation, phase transitions, and functional property tuning through dopant selection. Special emphasis is given to the role of rare-earth and transition metal elements, co-doping effects, and the formation of compositionally complex oxides. Across these systems, rare-earth A-site substitutions are frequently associated with improvements in magnetoelectric coupling and reductions in leakage currents. Additionally, the paper highlights application-specific functionalities, such as improved piezoelectricity, photocatalysis, and multiferroicity, pointing toward the future development of high-performance multiferroic devices. Quantitatively, doping strategies have been reported to increase saturation magnetization from < 1 emu/g in bulk BFO to similar to 10 emu/g in nanoparticles and up to similar to 50 emu/cm(3) (similar to 6 emu/g) in co-doped thin films. Remanent polarization values in modified films can reach 100-120 mu C/cm(2), while band gap tuning within similar to 2.0-3.2 eV demonstrates the versatility of compositional engineering. In several systems, electrical conductivity can change by more than three orders of magnitude depending on dopant type and concentration.