Structure and properties of the layered perovskites in Sm-Ba-Co-Fe-O System

Perovskite oxide materials with the general formula of ABO3, where A is an alkali earth or rare earth metals and B is transition metals, have attracted much attention as cathodes for solid oxide fuel cells because of their high electronic conductivity and fast mobility of oxygen ions. The introduction of Ba2+ and Ln3+ ions with significantly different radii into the A-sites leads to a formation of layered perovskite-type structures which have formed due to the cations’ ordering in the alternating layers. Depending on the nature of rare earth and 3d metal, it was possible to obtain double LnBaM2O6-δ, triple LnBa2M3O9-δ, or quintuple Ln2Ba3M5O15-δ perovskites. The aim of the present work was studying the effect of Ln/Ba and Fe/Co ratio for the crystal and defect structure and properties of oxides in the Sm-Ba-Co-Fe-O system. Polycrystalline samples of SmBaCo2−xFexO6-δ and Sm2-εBa3+εFe5-yCoyO15-δ were prepared by the glycine–nitrate synthesis. Final annealing was performed at 1100°С in air during 120h with intermediate grindings, followed by slow cooling down to room temperature at a rate of about 100°/h. The structural parameters were refined by the Rietveld method using the Fullprof-2008 software. Transmission electron microscopy studies were performed using FEI Tecnai G2 30 UT microscope operated at 300kV. The changes of oxygen content in complex oxides were measured by coulometric titration method as a function of temperature and oxygen partial pressure. The absolute value of oxygen content in the samples was determined using a direct reduction in the TG cell by hydrogen flow and red-ox titration. Thermal expansion of samples was studied using Netzsch DIL 402C dilatometer within the temperature range 25 – 1100°С in air. Total conductivity and Seebeck coefficient were measured simultaneously using a 4-probe technique. The crystal structure of SmBaCo2−xFexO6-δ (0≤x≤0.5) was described by the orthorhombic ap×2ap×2ap cell (Pmmm sp. gr.), while SmBaCo2−xFexO6-δ (0.6≤x≤1.1) crystallized in the tetragonal structure, ap×ap×2ap cell (P4/mmm sp. gr.). The crystal structure of single-phase Sm2-εBa3+εFe5-yCoyO15-δ (ε = 0, y = 0.5–1.5; ε = 0.125, y = 0) determined by XRD was described as cubic (sp. gr. Pm3m). However, transmission electronic microscopy revealed that oxides possess tetragonal structure with 5-fold c parameter. The defect structure of oxides with double perovskite structure was described using the model based on the simple cubic perovskite SmMeO3 (Me = Co, Fe) as a reference state. Equilibrium constants and enthalpies of the point defects formation were refined. The concentrations of all defect species were calculated as functions of temperature and oxygen nonstoichiometry. The temperature dependencies of total conductivity for SmBaCo2−xFexO6-δ and Sm2-εBa3+εFe5-yCoyO15-δ possess maxima at approximately 300–350ºC in air. The partial substitution of iron for cobalt leads to a decrease in the conductivity value. Seebeck coefficient for all compounds reveals positive values within the entire temperature and oxygen partial pressure ranges that indicate predominant p-type conductivity. The dependencies of electrical conductivity and Seebeck coefficient versus oxygen nonstoichiometry were discussed on the basis of the defect structure models. The values of activation energy for fixed oxygen content values were calculated. This work was supported by the Russian Science Foundation (Grant № 18-73-00159

Influence of nanotube length and density on the plasmonic terahertz response of single-walled carbon nanotubes

We measure the conductivity spectra of thin films comprising bundled single-walled carbon nanotubes (CNTs) of different average lengths in the frequency range 0.3-1000 THz and temperature interval 10-530 K. The observed temperature-induced changes in the terahertz conductivity spectra are shown to depend strongly on the average CNT length, with a conductivity around 1 THz that increases/decreases as the temperature increases for short/long tubes. This behaviour originates from the temperature dependence of the electron scattering rate, which we obtain from Drude fits of the measured conductivity in the range 0.3-2 THz for 10 $\mu$m length CNTs. This increasing scattering rate with temperature results in a subsequent broadening of the observed THz conductivity peak at higher temperatures and a shift to lower frequencies for increasing CNT length. Finally, we show that the change in conductivity with temperature depends not only on tube length, but also varies with tube density. We record the effective conductivities of composite films comprising mixtures of WS$_2$ nanotubes and CNTs vs CNT density for frequencies in the range 0.3-1 THz, finding that the conductivity increases/decreases for low/high density films as the temperature increases. This effect arises due to the density dependence of the effective length of conducting pathways in the composite films, which again leads to a shift and temperature dependent broadening of the THz conductivity peak.Comment: Submitted to Journal of Physics D. Main manuscript: 9 pages, 8 figures. Supplementary material: 5 pages, 6 figure

Conjugates of a Photoactivated Rhodamine with Biopolymers for Cell Staining

Conjugates of the photoactivated rhodamine dyes with biopolymers (proteins, polysaccharides, and nucleic acids) are important tools for microscopic investigation of biological tissue. In this study, a precursor of the photoactivated fluorescent dye (PFD) has been successfully used for staining of numerous mammalian cells lines and for conjugate formation with chitosan (“Chitosan-PFD”) and histone H1 (“Histone H1.3-PFD”). The intensive fluorescence has been observed after photoactivation of these conjugates inside cells (A431, HaCaT, HEK239, HBL-100, and MDCK). Developed procedures and obtained data are important for further application of novel precursors of fluorescent dyes (“caged” dyes) for microscopic probing of biological objects. Thus, the synthesized “Chitosan-PFD” and “Histone H1-PFD” have been successfully applied in this study for intracellular transport visualization by fluorescent microscopy

Local information transfer as a spatiotemporal filter for complex systems

We present a measure of local information transfer, derived from an existing averaged information-theoretical measure, namely transfer entropy. Local transfer entropy is used to produce profiles of the information transfer into each spatiotemporal point in a complex system. These spatiotemporal profiles are useful not only as an analytical tool, but also allow explicit investigation of different parameter settings and forms of the transfer entropy metric itself. As an example, local transfer entropy is applied to cellular automata, where it is demonstrated to be a novel method of filtering for coherent structure. More importantly, local transfer entropy provides the first quantitative evidence for the long-held conjecture that the emergent traveling coherent structures known as particles (both gliders and domain walls, which have analogues in many physical processes) are the dominant information transfer agents in cellular automata.Comment: 12 page

Inverted loss engineering in functional material covered waveguides

Optical waveguides, covered with thin films, which transmittance can be controlled by external action, are widely used in various applications from optical modulators to saturable absorbers. It is natural to suggest that the waveguide losses will be proportional to the covering material absorption. We demonstrate that under certain conditions this simple assumption fails. Instead, we observe the reduction of the film material absorption can lead to an increase in the waveguide propagation losses. For this, we use a side polished fiber covered with a single-walled carbon nanotube thin film whose absorption is attenuated either due to saturable absorption or electrochemical gating. For the films thicker than 50 nm, we observe saturable absorption to turn into light induced absorption with nonmonotonic dependence on the incident power. With a numerical simulation and analytical approach, we identify that this nontrivial behavior comes from mode reshaping and predict required parameters for its observation.Comment: 7 pages, 3 figure