06 Fakultät Luft- und Raumfahrttechnik und Geodäsie

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Author: search.filters.author.Fasoulas, StefanosSubject: search.filters.subject.670

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    Relation between crystal structure and transition temperature of superconducting metals and alloys
    (2020) Koblischka, Michael Rudolf; Roth, Susanne; Koblischka-Veneva, Anjela; Karwoth, Thomas; Wiederhold, Alex; Zeng, Xian Lin; Fasoulas, Stefanos; Murakami, Masato
    Using the Roeser-Huber equation, which was originally developed for high temperature superconductors (HTSc) (H. Roeser et al., Acta Astronautica 62 (2008) 733), we present a calculation of the superconducting transition temperatures, 𝑇𝑐, of some elements with fcc unit cells (Pb, Al), some elements with bcc unit cells (Nb, V), Sn with a tetragonal unit cell and several simple metallic alloys (NbN, NbTi, the A15 compounds and MgB2). All calculations used only the crystallographic information and available data of the electronic configuration of the constituents. The model itself is based on viewing superconductivity as a resonance effect, and the superconducting charge carriers moving through the crystal interact with a typical crystal distance, x. It is found that all calculated 𝑇𝑐-data fall within a narrow error margin on a straight line when plotting (2𝑥)2 vs. 1/𝑇𝑐 like in the case for HTSc. Furthermore, we discuss the problems when obtaining data for 𝑇𝑐 from the literature or from experiments, which are needed for comparison with the calculated data. The 𝑇𝑐-data presented here agree reasonably well with the literature data.
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    Influence of the sputtering technique and thermal annealing on YSZ thin films for oxygen sensing applications
    (2021) Paz Alpuche, Emilio; Gröger, Pascal; Wang, Xuetao; Kroyer, Thomas; Fasoulas, Stefanos
    Yttria-stabilized zirconia (YSZ) thin films were deposited using direct current (reactive and metallic) and radio frequency magnetron sputtering. The effect of the deposition technique and annealing treatment on the microstructure and crystallinity of the thin films was assessed. Using the films produced in this work, oxygen gas sensors were built and their performance under vacuum conditions was evaluated. All the films exhibited a cubic crystalline structure after a post-deposition thermal treatment, regardless of the sputtering technique. When the annealing treatment surpassed 1000 °C, impurities were detected on the thin film surface. The oxygen gas sensors employing the reactive and oxide-sputtered YSZ thin films displayed a proportional increase in the sensor current as the oxygen partial pressure was increased in the evaluated pressure range (5 × 10-6 to 2 × 10-3 mbar). The sensors which employed the metallic-deposited YSZ films suffered from electronic conductivity at low partial pressures.