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  • Author: A. Koňakovský x
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Effects of Slight Non-Stoichiometry in Sm-Ba-Cu-O Systems on Superconducting Characteristics

We studied the effects of slight Sm-Ba non-stoichiometry in Sm-Ba-Cu-O superconducting compounds on their transition, structural, and magnetic properties. Two series of single-phase samples of Sm1+xBa2-xCu3O7+Δ and Sm1+xBa2-xCu3O7+Δ with composition deviation from stoichiometry x from 0 to 0.1 were synthesized by the solid-state reaction method from Sm2O3, BaCO3 and CuO precursors and sintered at the temperature of ~ 1060 °C in flowing oxygen. All samples showed the values of Tc > 90 K and the volume density, p, 6.45 g cm-3 < p ≤ 6.73 g cm-3. The effect of the composite deviation of x on Tc, ΔTc, and volume magnetization M was studied. For Sm1+xBa2-xCu3O7+Δ compounds, optimal values of x were determined to maximize the width of the magnetization hysteresis at higher values of the applied magnetic field, corresponding mainly to the grain contribution. We also prepared the Sm1+xBa2-xCu3O7+Δ samples with x from 0 to 0.1 using the same processing conditions as in the case of A and B series. For the Sm1+xBa2-xCu3O7+Δ samples, values of x = 0.02 - 0.03 optimize Tc, ΔTc, Hp1 as well as M.

Automatic Apparatus for Simultaneous Measurement of Resistance and Inductance Temperature Transition Dependences of Superconductors

An automatic measurement complex for the study of transition properties of HTc superconductors using the transport method of the measurement of the resistance temperature dependence and the contactless mutual inductance method of the measurement of temperature dependence of the induced voltage based on the Meissner-Ochsenfeld effect have been developed. In addition, temperature dependences of harmonic components of the induced voltage may be measured simultaneously using the Brüel & Kjaer signal analyzer. Results of transport and induced voltage measurements are compared using YBCO superconductors with distinct grain and intergrain properties prepared by different technological procedures. The question of the mutual compatibility of such methods is discussed.

Synthesis and Transport Properties of Nanostructured VO2 by Mechanochemical Processing

The high-energy milling of the V2O5-Na2SO3 mixture in the range of 5 - 100 min leads to a synthesis of monoclinic VO2. The starting and minimum (at 220 °C) values of electric resistance R of the 100 min milled and pressed VO2-Na2SO4 mixture were 13.9 MΩ and 91.5 kΩ, respectively. The subsequent washing of the as-milled powder partially leads to the development of VO2 nanostructures with tube-like, sheet-like and rod-like morphology, besides VO2 (B) belt-like morphology, depending on the milling times.