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Open Access Dissertation

Keywords

High temperature superconductors;

Abstract

This research focused on (Tl0.5-xPb0.5-xEu2x)Sr2-y BayCa2Cu3Oz compound to determine the optimum y (Barium concentration), and then studied the effects of doping Eu in Tl, Pb sites. Studies on optimum y give rise to a high quality superconducting material as a target material for sputter deposition of thin films for electronics applications. Studies on doping Europium (Eu) is a new investigation and might lead to better understanding of the structural properties of the superconductor.

The experiment was conducted in three steps as follows:

  1. Optimizing the sample fabrication process by determining material sintering temperature in the furnace and sintering time in the air inside the Pt crucible.
  2. Set Tl/Pb = 1, and determine the optimum y in (Tl0.5xPb0.5)Sr2-y BayCa2Cu3Oz by trying different y, starting from y = 0.1 to 1.0.
  3. Determine the effect of Eu doping in Tl, Pb sites by experimenting different doping concentrations for Eu, starting from 1% to 10%.

Samples were prepared in two steps: precursor Sr-Ba-Ca- Cu-0 were synthesized first, starting from high purity BaO, CaO, CuO and SrO. The second step was to add the appropriate amount of PbO and TI2O3 (or Eu2O3 in case of Eu doping) toform the superconducting compound. Each sample was heat treated at 900°C for 24 hours twice and the pellets were made under the pressure of 15,000 PSI.

The (Tl0.5xPb0.5)Sr2-y BayCa2Cu3Oz superconductors with y varying from y = 0 to y = 1.0 were processed and sintered in air inside a Pt crucible at 880°C for 10 min. Sintered samples were characterized using the ac susceptibility and x-ray diffraction measurements.

From the AC susceptibility measurements, the critical temperature of the samples (Ba = 0.0 to Ba = 1.0) is between 100°K and 120°K. Sample with Ba doping of 0.75 showed the highest Tc of 118°K indicating the dominance of 1223 phase in this superconducting compound. The Barium concentration of 0.75 also shows higher magnitude of indicating higher volume fraction of superconductivity.

The powder x-ray diffraction measurements indicated that the strongest peak for the 1223 phase is the (105) peak close to 20 = 30°. At lower concentration of Ba below 0.5, the intensity of (105) peak is slowly increasing and then above0.5, the intensity of the 1223 peak improves, indicating the growth of significant 1223 phase in the superconductor. The sample is predominantly 1212 phase for Barium concentration below 0.5.

Other studies of importance in this research is the doping of Europium in Tl and Pb sites. Europium being a rare-earth metal offers the possibility of magnetic studies using Mössbaur spectroscopy. This gives an unique opportunity to study the structure of TlPbSrBaCaCuO superconductor precisely. As Eu concentration in the superconductor increases, the Tc decreases gradually. With the maximum doping fraction of 2x = 0.1, the Tc dropped close to 100°K from 118°K for 2x = 0.0. The magnitude of real part of susceptibility is higher than 1x10-3 (emu/gm) for Eu = 0, and decreases to 3x10-4 (emu/gm) . A notable observation in the Eu doping superconducting samples is the paramagnetic nature of the samples above the critical temperature.

Year of Submission

1996

Degree Name

Doctor of Industrial Technology

Department

Department of Industrial Technology

First Advisor

Mohammad F. Fahmy, Advisor

Second Advisor

Douglas T. Pine, Co-Advisor

Date Original

5-1996

Object Description

1 PDF file (ix, 134 pages)

Language

en

File Format

application/pdf

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