https://www.mpikg.mpg.de/th/people/dimova/publications/Dimova%20AdvCollInterfSci%2014.pdf

Recent developments in the field of bending rigidity measurements on membranes.

Oxygen determination from cell dimensions in YBCO superconductors

Several methods of chemical analysis, for example various redox titrations and thermogravimetric approaches, have been adapted to establish the oxygen content in superconducting cuprates and to determine the higher oxidation states of copper and other mixed-valent metals. The present review discusses and complements the authors' own experimental results on the oxygen content and metal valence analyses, but literature data from about 150 other references are reviewed as well.

https://iopscience.iop.org/article/10.1088/0953-2048/9/3/001/pdf

Determination of oxygen content and metal valences in oxide superconductors by chemical methods

Cation exchange modification of clinoptilolite – Screening analysis for potential equilibrium and kinetic adsorption separations involving methane, nitrogen, and carbon dioxide

We present first-principles calculations on systems consisting of a few layers of graphene and lithium. In particular, we investigate the evolution of the electron?phonon coupling strength with increasing number of layers. We find that, for intercalated systems such as C6-Li-C6 or C6-Li-C6-Li-C6, the electron?phonon coupling is weak. However, for systems of equal number of graphene and lithium layers, such as C6-Li or C6-Li-C6-Li, the electron?phonon coupling is strong. We investigate the optimal configuration that yields the highest superconducting transition temperature.

https://iopscience.iop.org/article/10.1088/2053-1583/1/2/021005/pdf

Superconductivity in graphene-lithium

Bulk Y1Ba2Cu3Oy superconductors with KClO3 or K2CO3 additives were synthesized by a solid state reaction method. The influence of additives on the AC susceptibility, morphology and microstructure of samples with nominal compositions Y1Ba2−xKxCu3Oy, Y1Ba2Cu3.5−xKxOy, Y1−0.2xBa2−0.2xKxCu3Oy, (x=0.2) were investigated. Experimental results showed a promoting effect of the additives on the formation of 123 phase in air atmosphere. Only traces of potassium were observed in all samples after the final backing, but chlorine was remained in the material. The superconducting transition temperature for all KClO3-doped samples was found to be higher than that for K2CO3-doped and undoped Y1Ba2Cu3Oy (YBCO). KClO3-doped Y1Ba1.8K0.2Cu3Oy with Tconset at 105 K was obtained. The comparison of characteristics for samples with various potassium compound in the initial batch demonstrated that each additive had a specific effect on χ(T), ΔTc and microstructure of YBCO high-temperature superconductors (HTSC). The results were discussed in terms of different interaction in which KClO3 and K2CO3 participate up to 900°C.

A study of the effect of KClO3 addition on the AC susceptibility and microstructure of high-temperature (Tconset at 105 K) YBCO ceramic superconductors

We report systematic studies of AC magnetic susceptibility and transport properties of Y 1− x Ca x Ba 2 Cu 3 O z bulk samples with 0⩽ x ⩽0.4. Single phase materials, reduction of carrier concentration and decrease of T c to 83 K were obtained at doping levels up to 20%. For Y 0.7 Ca 0.3 Ba 2 Cu 3 O z sample the improvement of grains boundary transport and screening capabilities has been observed as a result of the optimal ratio between carrier concentration and impurity phase BaCuO 2 presence. The appearance of bulk pinning and nonlinear effects starting at the highest temperature were detected also.

Effects of substituting calcium for yttrium on the superconducting properties of YBa2Cu3Oz bulk samples

Fully exchanged Ag-clinoptilolite prepared at 100°C using 1M solution of AgNO 3 was studied. The initial sample (Beli Plast deposit, Bulgaria) was enriched in clinoptilolite by a sequence of treatments – crushing, sieving, sedimentation, and separation with heavy liquids to obtain a content of about 93 wt.% of clinoptilolite intergrown with opal-C. Opal-C was subsequently removed by chemical treatment. Maximum cation exchange was reached on the seventh day (4.86(4) Ag atoms per formula unit). Rietveld structural refinement was then carried out on the Ag-exchanged clinoptilolite, and three independent Ag sites were localated in the channels of the clinoptilolite structure. Seven water sites, coordinating the Ag sites, were located. Ag-clinoptilolite is, potentially, a promising low-cost antibacterial material.

Preparation and Rietveld refinement of Ag-exchanged clinoptilolite

Copper(III) and total copper in superconducting Y-Ba-Cu oxide and related compounds can be determinated by two successive iodimetric titrations after the sample has been dissolved under Ar in HCl/KI medium. First, the iodine equivalent to copper(III) ist titrated with Na2S2O3 solution at pH 4.8, copper(II) being masked with EDTA. The total copper is then determined in the same solution by demasking with acid and iodide, followed by iodimetric titration. The method is both accurate and reproducible. The relative standard deviations for 1.074% copper(III) and 23.37% total copper are 0.8% and 0.3%, respectively.

Determination of Cu(III) and Cu(II) + Cu(III) in superconducting copper ceramics

Simple carbohydrates are associated with the enhanced risk of cardiovascular disease and adverse changes in lipoproteins in the organism. Conversely, sugars are known to exert a stabilizing effect on biological membranes, and this effect is widely exploited in medicine and industry for cryopreservation of tissues and materials. In view of elucidating molecular mechanisms involved in the interaction of mono- and disaccharides with biomimetic lipid systems, we study the alteration of dielectric properties, the degree of hydration, and the rotational order parameter and dipole potential of lipid bilayers in the presence of sugars. Frequency-dependent deformation of cell-size unilamellar lipid vesicles in alternating electric fields and fast Fourier transform electrochemical impedance spectroscopy are applied to measure the specific capacitance of phosphatidylcholine lipid bilayers in sucrose, glucose and fructose aqueous solutions. Alteration of membrane specific capacitance is reported in sucrose solutions, while preservation of membrane dielectric properties is established in the presence of glucose and fructose. We address the effect of sugars on the hydration and the rotational order parameter for 1-palmitoyl-2-oleoyl-sn-glycero-3- phosphocholine (POPC) and 1-stearoyl-2-oleoyl-sn-glycero-3- phosphocholine (SOPC). An increased degree of lipid packing is reported in sucrose solutions. The obtained results provide evidence that some small carbohydrates are able to change membrane dielectric properties, structure, and order related to membrane homeostasis. The reported data are also relevant to future developments based on the response of lipid bilayers to external physical stimuli such as electric fields and temperature changes.

A. Stoyanova-Ivanova

Papers

A study of the effect of KClO3 addition on the AC susceptibility and microstructure of high-temperature (Tconset at 105 K) YBCO ceramic superconductors

Effects of substituting calcium for yttrium on the superconducting properties of YBa2Cu3Oz bulk samples

Preparation and Rietveld refinement of Ag-exchanged clinoptilolite

Determination of Cu(III) and Cu(II) + Cu(III) in superconducting copper ceramics

Dielectric Properties of Phosphatidylcholine Membranes and the Effect of Sugars.