Browsing by Author "Mikli V."

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    Influence of the preparation method on the As-Se-AgI thin films behaviour
    (2008-05-01) Hineva T.; Petkova T.; Petkov P.; Mikli V.; Socol G.; Mihailescu C.; Mihailescu I.
    Bulk glasses of the (As2Se3)1-x (AgI) x and (AsSe)1-x(AgI)x systems, where x 5, 10, 15 up to 35 mol.% have been prepared by the melt-quenched technique. The thin films have been deposited by means of vacuum thermal evaporation (VTE) and pulsed laser deposition (PLD). The XRD investigation reveals a generally amorphous structure; small peaks are only observed in the samples with the highest AgI. The film compositions have been determined by EDS (energy dispersive X-ray microanalysis). WDS (wavelength dispersive spectroscopy) studies have shown that the films do not contain oxygen within the accuracy of the method (1 %). The films are dense with smooth surface as revealed by using scanning electron microscopy (SEM) and atomic force microscopy (AFM). © 2008 IOP Publishing Ltd.
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    Phase formation and microstructure in Re1-xCax Ba2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics
    (2006-03-01) Stoyanova-Ivanova A.; Terzieva S.; Staneva A.; Mikli V.; Traksmaa R.; Dimitriev Y.; Kovachev V.
    We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-xCax Ba2Cu3O7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.
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    Phase formation and microstructure in Re1-xCax Ba2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics
    (2006-03-01) Stoyanova-Ivanova A.; Terzieva S.; Staneva A.; Mikli V.; Traksmaa R.; Dimitriev Y.; Kovachev V.
    We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-xCax Ba2Cu3O7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.
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    Structural investigation of tellurium based thin films
    (2018-01-01) Ivanova V.; Trifonova Y.; Lilova V.; Mikli V.; Stoyanova-Ivanova A.
    Tellurium based materials possess a low temperature phase change transition. Sometimes they cannot be obtained in an amorphous state under normal conditions. Thus they can be used as an active element in phase change memory devices. Our study is dedicated to the synthesis of tellurium based materials using the systems (GeTe3)100-xInx, x = 5 mol %, 10 mol %, 15 mol % and 20 mol % and (GeTe4)100-xInx, x = 5 mol %, 10 mol %, 15 mol % and 20 mol %, the deposition of thin films on their ground and the investigation of their morphology, topology and structure aiming to obtain new knowledge for evaluation of the possibility for application of these materials in phase change memory devices.
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    Synthesis and superconducting properties of Nd0.33 Eu0.08Gd0.58Ba2Cu3 Oz materials
    (2008-03-01) Stoyanova-Ivanova A.; Terzieva S.; Shivachev B.; Mikli V.; Vladimirova L.
    We have studied the effect of the ratio of different rare-earth element on the superconducting properties and phase formation of (Nd0.33Eu0.08Gd0.58)Ba2 Cu3Oz ceramic. Bulk NEG samples were prepared using the solid-state reaction process. The superconducting transition for Nd0.33Eu0.08Gd0.58Ba2 Cu3Oz is Tc ≈ 90 K and the value of the critical current density (Jc) is 13.9 A/cm2 at 77 K under zero magnetic fields. This value is twice as high when compared with the (Jc) value of YBCO systems (J3 = 7.31 A/cm2). The obtained bulk sample was used for the production of superconducting Ag-sheathed tapes by OPIT method including hot rolling. The critical current density of the obtained tape (337 A/cm2) is one order higher than the one of the bulk sample. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2008.