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Title of Thesis

Institute/University/Department Details
University of Karachi/ Department of Physics
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
silver based conducting glasses, dielectric polarisation, insulators, conductor, glass, glass transition, borophosphate glasses, borate glasses, phosphate glasses, thermal characterization

The dielectric response of silver phosphate and silver borophosphate glasses has been investigated between 10-3-105 H2 with temperature and composition as parameters using a fully automated measuring system based on Solartron Frequency Response Analyser (1255 F.R.A). These oxide glasses were prepared and studied in three different configuration, viz. [(x) Ag2O(100-x)P2O5], [50Ag2O(x)B2O3 (50-x) P2O5] and [60Ag2O:(x)B2O3(40-X)P2O5] covering a wide range of low and high conducting glasses.

It has been found that the domination of a quasi-direct current (Q-dc) process is the common feature of the dielectric spectra of these glasses. For a Q-dc process the real and imaginary components of the complex susceptibility follow fractional power law dependence on frequency with the exponent p less than, but close to unity. This incomplete transport of charge through limited paths between the electrodes causes an anomalously large frequency dependent polarisation and hence and hence capacitance.

The studied silver based ion conducting glasses have shown a strong dependence on the composition of these glasses. It has been observed that the Q-dc region for [(x)Ag2O(100-X)P2O5] glasses is well developed at low frequencies and is followed b a frequency and temperature independent capacitance, C(∞) at higher frequencies. For [50Ag2O:(x)B2O3(50-X)P2O5) glasses a low frequency electrode phenomenon of Maxell-Wagner type has been found to overlap with a diplolar phenomenon at higher frequencies. Diffusive barrier regions have been found in [60Ag2O(x)B2O3:(40-X)P2O5) glasses with a characteristic lowest frequency slope of 0.5.

It has been found that the gradual substitution of B2O3 in the glassy net-work influences the dielectric response and introduces an imperfect charge transport process (Q-dc) of limited charge transport in place of bulk conduction, at higher frequencies and effects the diffusion barrier at the electrodes to make them, slightly more conductive at the lowest frequencies for [60Ag2O(x)B2O3:(40-X)P2O5) glasses. The magnitudes of the activation energies of conduction and dielectric relaxation have been found approximately same ad have been attributed to a closely related thermally activated localized hopping mechanism of silver ions between the neighboring sites.

The power law dispersions for the bulk and the surface layer of [Ag2O:B2O3:P2O5] glasses have also been modeled mathematically using frequency dependent resistive and capacitive elements in a conventional equivalent R-C network. A response function, C(ω) (iω) –P /[1+(iω) S-P] with both the exponents p and s positive and less than 1 has been proposed which successfully modeled the experimentally observed dielectric response.

Download Full Thesis
1576.87 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
121.4 KB
2 1 Dielectric Theory
208.69 KB
  1.1 Introduction 21
  1.2 Insulators And Conductor 21
  1.3 Polarisation 22
  1.4 Analytical Treatment Of Dielectric Polarisation 25
  1.5 Time Dependent Dielectric Response 28
  1.6 Frequency Dependent Dielectric Response 31
  1.7 Permittivity Conductivity And Loss. 33
  1.8 Time Dependence Of Relaxation 35
  1.9 Power Law Dielectric Response 39
  1.10 Response Functions 43
  1.11 References 48
3 2 Preparation And Characterization Of Glasses
119 KB
  2.1 Introduction 50
  Glass And Glass Transition 50
  2.3 Glass Formation 54
  2.4 Preparation Of Amorphous Materials. 58
  2.5 Physical Characterization Of Glasses 60
  2.6 Electrical Characterization 62
  2.7 References
4 3 Experimental Setup And Analytical Techniques
204.6 KB
  3.1 Part A: Introduction 66
  3.2 Sample Preparation 67
  3.3 Dielectric Spectrometer 72
  3.4 Frequency Response Analyser Measuring Procedure 74
  3.5 Low And High Temperature Measurements 76
  3.6 Part – B: Introduction 79
  3.7 Simple A.C. Impedance Theory 81
  3.8 Frequency Domain Response 85
  3.9 Separation Of Overlapping Processes 86
  3.10 Subtraction Of C∞. 88
  3.11 Normalisation Technique 89
5 4 Structure Of Borate, Phosphate And Borophosphate Glasses Ad Survey Of Previous Work
246.96 KB
  4.1 Introduction 96
  4.2 Borate Glasses 98
  4.3 Phosphate Glasses 101
  4.4 Borophosphateglasses 102
  4.5 Brief Survey Of Previous Work 104
6 5 Physical And Thermal Characterization Of Silver Phosphate And Silver Borophosphate Glasses
101.37 KB
  5.1 Introduction 126
  5.2 Density, Oxygen Packing Density And Silver Ion Concentration, Measurements And Results 127
  5.3 X-Ray Diffraction (Xrd) Results 130
  5.4 Summary 138
  5.5 References 139
7 6 Effect Of Electrode Materials On A [60ag 2 o:06b 2 o 3 :34p 2 o 5 ] Glass
276.62 KB
  6.1 Introduction 110
  6.2 Impedance Plots Of A Dispersive Network 142
  6.3 Effect Of Electrode Materials Or The Dielectric Response (Temperature Measurement) 14
  6.4 Comparison Of Results For Various Electrode Systems 164
  6.5 Conclusion 171
  6.6 References 172
8 7 Measurements On [50ag 2 o:Xb 2 o 3 (50-X)P 2 o 3 ] Glasses
239.69 KB
  7.1 Introduction 173
  7.2 Results And Discussions On The Dielectric Responses Of [50ag 2 o:Xb 2 o 3 (50-X)P 2 o 5 ] Glasses 173
  7.3 Conclusion 199
  7.4 References 202
9 8 Measurements On [60ag 2 o:Xb 2 o 3 :(40-X)P 2 o 5 ] Glasses
280.53 KB
  8.1 Introduction 204
  8.2 Results And Discussions 205
  8.3 Conclusion 234
  8.4 References 237
10 9 Discussion And Conclusion
67.35 KB
  9.1 Discussion 238
  9.2 Conclusion 241
  9.3 References 245
  9.4 List Of The International Publications Based On The Results Extracted From This Thesis 245