Eugene A. Goodilin

On the stability region and structure of the Nd1+xBa2−xCu3Oy solid solution

Abstract We studied the low and upper stability boundaries and the structure evolution of the Nd 1+ x Ba 2− x Cu 3 O z solid solution along its single-phase field. It was found that in oxygen the limit of the solid solution extends up to Nd 1.9 Ba 1.1 Cu 3 O z at 950–1050°C while at lower and higher temperatures it becomes narrower. In nitrogen atmosphere the substitution range is much smaller and x does not exceed 0.3 at 800°C. The replacement of Ba 2+ by Nd 3+ is accompanied by decreasing both a and c lattice constants of quenched samples. At the same time in oxygen at x ≥ 0.6 ordering phenomena occur leading to the orthorhombic distortion of the tetragonal subcell. A model of the solid solution crystal structure with a B-centered unit cell and lattice parameters a = 2 a sub , b = b sub and c = 2 c sub was suggested and refined.

Oxygen nonstoichiometry and phase transitions of the neodymium-rich Nd1+xBa2−xCu3Oz solid solution

Abstract On the basis of chemical, thermal analysis and Cu K-edge X-ray absorption measurements, oxygen content in the Nd 1+ x Ba 2− x Cu 3 O z solid solution was determined between 1000°C in air and 400°C in oxygen for x =0.05–0.9 compositions. It has been observed that the oxygen nonstoichiometry Δ z of the Nd 1+ x Ba 2− x Cu 3 O 7+ x /2−Δ z solid solution decreases 2–2.5 times for a large substitution (Δ z ≈0.3–0.33 for x =0.9), despite of the acclaimed higher total oxygen content. The difference in nonstoichiometry is explained by a higher average value of the copper oxidation state (ACV), which is vital for the solid solution with large x even at elevated temperatures (ACV≈2–2.05 for x >0.3 at 1000°C, P O 2 =0.21 atm). On the contrary, the ACV after complete oxygenation is almost constant (about 2.25–2.3) for the whole series. The x -dependence of the oxygen content is not monotonous and structural phase transitions can be observed at x =0.3 and x =0.6, as confirmed by the X-ray diffraction and the Raman scattering spectroscopy. The first well-known transition is connected with the oxygen disorder due to the Nd substitution for Ba at random Ba-sites. In the present work, it is proved by the apical oxygen mode broadening in Raman spectra. Ordering of the Nd and Ba atoms with a subsequent orthorhombic distortion of the lattice may occur even at 1000°C in air due to the second transformation at x ≈0.6. The invariable orthorhombicity of the Nd-rich solid solution with x >0.6 is not caused by the oxygen absorption as in the x =0.05 case. Existence of high- and low-temperature orthorhombic modifications of this solid solution has been observed for the first time. Finally, a tentative 3D ( z – x – T ) diagram is suggested for the Nd 1+ x Ba 2− x Cu 3 O z solid solution up to 1000°C in air, including the new x =0.6–0.9 region.

Planar SERS nanostructures with stochastic silver ring morphology for biosensor chips

Surface-enhanced Raman spectroscopy (SERS) of living cells has rapidly become a powerful trend in biomedical diagnostics. It is a common belief that highly ordered, artificially engineered substrates are the best future decision in this field. This paper, however, describes an alternative successful solution, a new effortless chemical approach to the design of nanostructured silver and heterometallic continuous coatings with a stochastic “coffee ring” morphology. The coatings are formed from an ultrasonic mist of aqueous diamminesilver hydroxide, free of reducing agents and nonvolatile pollutants, under mild conditions, at about 200–270 °C in air. They consist of 30–100 micrometer wide and 100–400 nm high silver rings composed, in turn, of a porous silver matrix with 10–50 nm silver grains decorating the sponge. This hierarchic structure originates from ultrasonic droplet evaporation, contact-line motion, silver(I) oxide decomposition and evolution of a growing ensemble of silver rings. The fabricated substrates are a remarkable example of a new scalable and low cost material suitable for SERS analyses of living cells. They evoke no hemolysis and reduce erythrocyte lateral mobility due to suitable “coffee ring” sizes and a tight contact with the silver nanostructure. A high SERS enhancement, characteristic of pure silver rings, made it possible to record Raman scattering spectra from submembrane hemoglobin in its natural cellular environment inside single living erythrocytes, thus making the substrates promising for various biosensor chips.

Construction of a quasi-ternary phase diagram in the NdO1.5BaOCuO system in the air atmosphere Part II. Phase equilibria of the neodymium-rich Nd1+xBa2−xCu3Oz solid solution

Abstract In the present work phase relations in a copper-rich corner of the NdO 1.5 BaOCuO system were studied at 970–1060°C in air by DTA, quenching experiments, EPMA, XRD, ICP AES and finally confirmed by growth of several test single crystals. It was found that in the analyzed region the Nd 1+ x Ba 2− x Cu 3 O z solid solution (Nd123ss) with maximum x values co-exists at 970–1060°C with Cu-rich melt and different solid phases: CuO (970–990°C), Nd 2 CuO 4 (990…995–1045°C) or Nd 4 Ba 2 Cu 2 O 10 (1060°C). The decomposition temperature of Nd123ss decreases with increasing the neodymium content, and the limit composition of Nd123ss extends up to Nd 2 BaCu 3 O z at 990–995°C. The Nd123ss unit cell volume deviations from the ideal solution of the Nd123 and Nd213 phases were found positive by XRD, as well as their excess Gibbs energy of mixing, estimated thermodynamically using the experimental phase diagram. This provides a probability of a spinodal decomposition phenomena of such a solution.

Probing cytochrome c in living mitochondria with surface-enhanced Raman spectroscopy

Selective study of the electron transport chain components in living mitochondria is essential for fundamental biophysical research and for the development of new medical diagnostic methods. However, many important details of inter- and intramembrane mitochondrial processes have remained in shadow due to the lack of non-invasive techniques. Here we suggest a novel label-free approach based on the surface-enhanced Raman spectroscopy (SERS) to monitor the redox state and conformation of cytochrome c in the electron transport chain in living mitochondria. We demonstrate that SERS spectra of living mitochondria placed on hierarchically structured silver-ring substrates provide exclusive information about cytochrome c behavior under modulation of inner mitochondrial membrane potential, proton gradient and the activity of ATP-synthetase. Mathematical simulation explains the observed enhancement of Raman scattering due to high concentration of electric near-field and large contact area between mitochondria and nanostructured surfaces.

A simple method of growth and lithiation of Ba6Mn24O48 whiskers

Isothermal crystal growth from evaporating fluxes of alkaline chlorides allowed the reproducible, high yield synthesis of micron thick and millimetre long whiskers of two manganese-rich phases, BaMn8O16 hollandite and Ba6Mn24O48 manganite, with a tunnel crystal structure. The crystal morphology suggests that they grow by a VLS (vapour–liquid–solid)-related mechanism. An ion exchange in molten LiNO3 at about 300 °C was found to introduce lithium in structural channels of the Ba6Mn24O48 phase due to partial barium substitution.

Solubility of neodymium in copper-rich oxide melts in air and growth of Nd1 + xBa2 − xCu3Oz solid solution single crystals

Abstract In the present work temperature dependencies of neodymium solubility in Ba-Cu-O fluxes of different compositions were investigated under the ambient air condition. Small amounts of samples were taken from thermally equilibrated melts in MgO crucibles at 1000–1065°C and the compositions were analyzed by the inductively coupled plasma spectroscopy (ICP) technique. The obtained data were compatible with DTA measurements and results of quenching experiments. The maximum solubility of neodymium in the liquid of about 7 at% achieves in the ‘Nd 2 CuO 4 -L’ field at the highest investigated temperature (1065°C) and for the copper-richest fluxes (Cu:Ba = 6:1). The dissolution enthalpy of the Nd 2 CuO 4 phase in this flux was estimated experimentally to be 115 kJ/mol. Based on the experimental solubility data, single crystals of the Nd 1 + x Ba 2 − x Cu 3 O z solid solution (x = 0.43 − 0.85) with non-metallic resistivity behaviour after oxygen annealing were grown by the TSSG method.

Lithium peroxide crystal clusters as a natural growth feature of discharge products in Li–O2 cells

Summary The often observed and still unexplained phenomenon of the growth of lithium peroxide crystal clusters during the discharge of Li–O2 cells is likely to happen because of self-assembling Li2O2 platelets that nucleate homogeneously right after the intermediate formation of superoxide ions by a single-electron oxygen reduction reaction (ORR). This feature limits the rechargeability of Li–O2 cells, but at the same time it can be beneficial for both capacity improvement and gain in recharge rate if a proper liquid phase mediator can be found.

Combined Raman and atomic force microscopy study of hemoglobin distribution inside erythrocytes and nanoparticle localization on the erythrocyte surface

The letter describes a combined technique of atomic force microscopy (AFM) and micro-Raman spectroscopy (mRS) to estimate the distribution of cytosolic hemoglobin (Hb) and nanoparticles (NPs) inside and on the erythrocyte surface, respectively. We have shown that cytosolic hemoglobin is distributed uniformly inside the cell while NPs absorb on the cell surface irregularly, forming nanoaggregates. The obtained data provide new insight into the surface enhanced Raman spectroscopy of living cells.

Chemical tuning of adsorption properties of titanate nanotubes

A conventional hydrothermal method widely used for the preparation of titania-based nanotubes still generates many unsolved questions. One of them is definitely connected with the influence of a posthydrothermal treatment of titania nanotubes on their micromorphology, structure, and adsorption characteristics. Here, it was analyzed systematically by a group of methods including nitrogen adsorption and temperature-programmed desorption of ammonia and carbon dioxide. It is proved that adsorption characteristics and the surface state of titania nanotubes correlate with a sodium content, since sodium ions act as Lewis acid sites and shield Ti4+ acid sites of the nanotubes. To obey a balance between chemical and heat treatments of the nanotubes to design their functional properties has been suggested.