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Synthesis and Investigation of Effect of Pr Doping on the Compound Y(3-x) Pr x Ba5 Cu8 O(19-δ)-F

Jafari Gharyeh Ali, Hamid Reza | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50795 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Akhavan, Mohammad
  7. Abstract:
  8. Synthesis and Investigation of Effect of Pr Doping on the Compound Y_(3-x) 〖Pr〗_x 〖Ba〗_5 〖Cu〗_8 O_(19-δ)-FInvestigation of doping of the parent compounds with different elements is important to understand the origin of high-Tc superconductivity. Several research groups have attempted to improve the properties of superconductivity and better understand the superconductivity mechanism of cuprate through doping different elements. In this research, at first, optimization of Y_3 〖Ba〗_5 〖Cu〗_8 O_(19-δ) F_z samples with z=0.2 ,0.4 ,0.6 ,0.8 ,1 ,2 ,3 ,4 have been done. By doping fluorine instead of oxygen, we expected an increase in the transition temperature, based on some the reports. But after composing a variety of samples and studying them, we found no significant change in the transition temperature of these compositions. Fluorine doping causes a decrease in the resistance of the samples’ normal state and a narrower transition width. In order to have the least transition width and low normal phase resistance, z=0.4 was selected as the optimum amount of fluoride for the simultaneous doping of praseodymium in the samples Y_(3-x) 〖Pr〗_x 〖Ba〗_5 〖Cu〗_8 O_(19-δ) F_0.4 with x= 0.05 ,0.1 ,0.2 ,0.3 ,0.4 ,0.5 ,0.8 ,1.0 ,1.2 ,1.5 ,1.8 . All the samples had two-step transitions in which the second transition temperature was decreased and the transition width of the samples were increased by increase of doping value. It seems that the effects of Y358 composition doping with fluorine and praseodymium on the transition temperature have had the same origin. Probably, by substitution of F and Pr, the amount of oxygen has changed in the sample which might have caused a decrease in the effective carriers and as a result a decrease in the transition temperature and an increase in the transition width. Furthermore, it was observed that with Pr doping, a transition occurs from the metal to the semiconductor in the amount of x≥0.3 which is different from that of Y_1 〖Ba〗_2 〖Cu〗_3 O_(7-δ) compositions. Analysis of the results of the X-ray diffraction spectrum indicates formation of phases Y_(3-x) 〖Pr〗_x 〖Ba〗_5 〖Cu〗_8 O_(19-δ) and Y_3 〖Ba〗_5 〖Cu〗_8 O_(19-δ) F_z in the sample. In addition, by applying Maud software and using the Rietveld analysis method, the lattice parameters were obtained for these compounds. Moreover, by determining the average crystallite size from X'Pert HighScore program, samples prepared with different doping of praseodymium, generally indicates a reduction in the size of the grains with an increase in the value of Pr up to x = 1.8 and as a result a decrease in the quality of the superconducting sample
  9. Keywords:
  10. Praseodymium Doping ; Superconductivity ; Fluorine Doping ; Cuprate Superconductors

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