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Determination of Stable Crystal Structure of Y358 New Superconductor and its Phonon and Electronic Structure using Density Functional Theory

Rasti, Mohammad | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44374 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Khosroabadi, Hossein; Akhavan, Mohammad
  7. Abstract:
  8. Y-based Superconducting compounds (YBCO) with different stoichiometry have been considered by researchers for its transition temperature above the boiling temperature of liquid nitrogen, preparation of high quality samples, simple crystal and electronic structure and other advantages relative to the other high-Tc copper oxide superconductors. Reaching to higher transition temperature has been considered in the recent years. In 2009, new compound of this family with different stoichiometry Y3Ba5Cu8O18(Y358) and transition temperature above 100 K was synthesized which is 10 K higher than maximum transition temperature in this family. Confirming this transition temperature can be help us for discovering new superconductors of this family. Other reports have been confirmed the formation of this phase, too, however because of difficulty single phase preparation, analyzing the experimental result about determination of crystal structure is difficult such that there are some discrepancies about lattice parameters and crystal symmetry in different reports. Because of high importance of structural details and relative coordination of ions in unit cell in superconducting properties of this system, calculations of determination and optimization of crystal structure is the first step for confirming the formation of this phase. So, using computational Quantum Espresso software based on density functional theory, equilibrium energy for three structures which could be candidate for this compound, has been calculated and static and elastic stability conditions was investigated. Also, Phonon calculations was performed to investigating of dynamical stability of structures. In addition, electronic structure of this compound has been calculated for determination of electronic properties and probability of superconducting transition at T > 100 K in comparison with other superconductors in this family
  9. Keywords:
  10. YBCO Superconductor ; Crystalline Structure ; Electron Structure ; Structural Optimization ; Density Functional Theory (DFT) ; Y358 Supperconductor ; Crystal Structure Symmetry

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