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Preparation and Characterization of LaOFeAs Iron based Superconductor by Solid State Reaction

Marzough, Elahe | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47080 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Khosrovabady, Hossein; Akhavan, Mohammad
  7. Abstract:
  8. The discovery of superconductivity in compounds containing magnetic elements such as Iron, Cobalt and Nickel has attracted the attention of many researchers in last few years. Before the discovery of superconductivity in LaOFeP it was believed that the superconductivity and magnetic properties are in conflict to each other. Untill now, variety of researches in Iran has been done on preparation and characterization of Copper oxide superconductors without any attention to the Iron based superconductors. Accordingly, the main purpose of this thesis is preparation and optimization of LaOFeAs as the basis compound of 1111 Iron based superconductors using the solid state reaction method. This compound has the capability to be a superconductor with Tc above the 57 K by a suitable doping of fluorine, other rare earth elements, reduction of Oxygen and applying pressure.
    Regarding the gradual sublimation of Arsenic at temperatures about 600 ºC, the pre mixed of FeAs compound was prepared and all thermal process have been done on sealed silica tube. By preparing several FeAs samples it has concluded that the steam removal in quartz capsule would increase the quality of samples at initial preparation steps. It has also concluded that the maximum temperature of 700ºC is suitable and gradual increase of temperature is necessary to find good quality FeAs samples.
    The analysis of XRD patterns of this compound by Xpert HighScore confirms the desired phase formation and its crystal parameters have also been determined. The SEM pictures show the homogenous granular structure with Pentagon shape grains around 10 micron size in each side. The LaOFeAs with the pre mixed FeAs, La and La2O3 powders were prepared by one step and two steps solid state reaction method. The XRD analysis shows that the two steps process is more appropriate for obtaining high quality single phase samples. The EDX, SEM, XRD and ICP measurements were done for analyzing the microscopic quality of the samples. The XRD analysis of the first sample shows the formation of unwanted phases. By using the DTA/TG results, some of the preparation conditions were modified and eventually more suitable samples were prepared. The formation of LaOFeAs tetragonal phase with a=b=3.873 and c=8.544 Å successfully obtained in final samples. We hope this study be a useful base for the future investigations of iron-based 1111 superconductors
  9. Keywords:
  10. Iron Based Superconductor ; Solid State Reaction ; Structural Analysis ; Element Analysis

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