I= IMPEDANCE SPECTROSCOPIC STUDIES OF SOME HIGH Tc SUPERCONDUCTORS
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Title of Thesis
IMPEDANCE SPECTROSCOPIC STUDIES OF SOME HIGH Tc SUPERCONDUCTORS

Author(s)
Sabahat Yasmeen
Institute/University/Department Details
Department of Chemistry/ Quaid-i-Azam University, Islamabad
Session
2001
Subject
Chemistry
Number of Pages
230
Keywords (Extracted from title, table of contents and abstract of thesis)
impedance spectroscopic studies, tc superconductors, sintering condition, conductivity, superconductivity, resistivity, x-ray diffraction, impedance

Abstract
In the present study RBa2Cu3O7-8 (R = Y, Dy and Ho) samples been studied with a view to analyze the effect of sintering condition, area of contact and temperature on superconducting properties. Resistance verses temperature studies and X-Ray diffraction measurements were carried out for determining transition temperatures and lattice parameters respectively. Y Ba2Cu3O7-8 and Dy Ba2Cu3O7-8 samples show semiconducting behavior before their final sintering whereas Ho Ba2Cu3O7-8 sample shows superconducting transition before its final sintering. The reproducibility of the Ho Ba2Cu3O7-8 sample was checked by repeated preparations. Tc of all the superconducting samples was found -89K. In each case orthorhombic 1-2-3 type structures (Pmmm Symmetry) have been found with minimal change observed in c-parameter.

Impedance studies were carried out on the samples before final sintering (BFS) and after final sintering (AFS) conditions in the following modes of contact:

1. contacts on same side

2. contacts on opposite sides.

The ac impedance studies were done in the frequency range of 1 Hz to 100 kHz and at different temperatures ranging from room temperature down to 78 K. Various Impedance parameters (such as) bulk resistance Rb, grain boundary resistance Rgb. double layer capacitance Cdl, grain boundary capacitance Cgb and inductance L were obtained through impedance simulation using EQUIVCRT (computer simulation software). Different types of impedance plots such as Nyquist plot, Bode plot, modified Nyquist plot, phase angle plot, log Vitro vs. log f and log Yr/ro vs log f were obtained from TFA impedance analyzer. Impedance results were analyzed using equivalent circuits and simulation.

The ac conductivity plots (log O'R vs. log of 00) were also obtained at temperatures from ambient down to 77K, which gave information about the slope related parameters Le. effective barrier height, binding energy and hopping distance. Relaxation phenomenon was also studied by evaluation of relaxation constants from various impedance and conductivity plots. The net relaxation is found to be considered due to grain boundaries.

Attempts were also made to empirically fit the ac data in the universal equation and in the RWT model by using a homemade computer program, which showed good agreement between experimental and bestfit results at high frequencies. At both the sintering conditions the impedance and ac conductivity studies gave supportive information about the presence of conductive grain boundaries as weak links in these superconducting ceramics.

Download Full Thesis
5831.62 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
358.41 KB
2 2 Impedance, Ac Conductivity And Superconductivity 11
231.39 KB
  2.1 Impedance 11
  2.2 Electrical Conductivity 19
  2.3 AC Conductivity 22
  2.4 Superconductivity 28
3 3 Experimental 35
290.13 KB
  3.1 Chemicals 35
  3.2 Sample Preparation 35
  3.3 Resistivity , X-Ray Diffraction, And Impedance Measurement Techniques And Instrumentation 39
4 4 Results And Discussion 52
4681.98 KB
  4.1 Resistance Vs Temperature Measurement 54
  4.2 X-Ray Diffraction 65
  4.3 Impedance Studies 78
  4.4 AC Conductivity Studies 98
5 5 References 187
249.93 KB