(1990) High temperature ceramic superconductors: oxalate co-precipitation procedure for synthesis and influence of compositional variations. Masters thesis, King Fahd University of Petroleum and Minerals.
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English Abstract
The objectives of the present thesis were mainly directed towards the development of new preparative procedures, rather than to prepare altoghether new high-T materials, and to study the effects of compositional variations using measurements such as X-ray Powder Diffraction (XFD), Scanning Electron Microscope (SEM), Energy Dispersive X-ray-Spectroscopy (EDS), and Resistance versus Temperature. Twenty-two superconducting samples of multi-component oxide having 21- and 23- structures, beside five non-superconducting samples, were prepared using oxalate co-precipitation method starting with reagent grade, rather than high-purity materials. A systematic subsituation of Sr by Ba and/or Ca ions was carried out in the 21-structure ternary oxides having stiochiometry La Sr Co , to produce 4- and 5-component metal oxides of the La Sr - AE C O series where AE = Ba and/or Ca. Similarly, a systematic substitution of Y by Gd ions in 123-structures was carried out to produce 4- and 5-component metal oxides of the type Y Gd Ba Cu O where 0<B<0.5. Similar procedure was used for all samples of both types of superconductors to generalize our preparation techniques. The conditions for co-precipitation, annealing, pulverization, effects of oxygen atmosphere, reaction with porcelain crucible and other processes were optimized for various compositions. X-ray powder diffraction (XFD) patterns confirmed the presence of a tetragonal phase all La-(Sr/Ba/Ca) CuO series and the non-superconducting RE-Ba-CuO samples. The presence of an othorhombic phase was confirmed for all superconducting RE-Ba -Cu O ceramic systems. Scanning Electron Microscopy (SEM) indicated the presence of grain sizes in the range of 0.3 to 15.0 mu, while Energy Dispersive X-ray Spectroscopy (EDS) indicated the presence of La:AE ration of 2:1 for La-(Sr/Ba/Ca)CuO and 123 for Y:Ba:Cu for the (Y/Gd)-Ba-CuO series. The resistance versus temperature measurements indicate Sr being the best alkaline-earth metal among Ca, Ba and Sr for the ternary La-containing ceramics since substitution or doping of Ca and/or Ba for Sr decreased the Tc of these 21-structures. The resistance versus temperature data for 123-strucgtures indicated that Y is the best choice among Gd and Y in the RE-Ba Cu O series. Substitution or doping of Gd for Y decreased the Tc to a lower value from 96K to about 91K.
| Item Type: | Thesis (Masters) |
|---|---|
| Subjects: | Chemistry |
| Department: | College of Chemicals and Materials > Chemistry |
| Committee Advisor: | Hussain, M. S. |
| Committee Members: | Haque, Mazhar-ul and Khattak, Guldad K. |
| Depositing User: | Mr. Admin Admin |
| Date Deposited: | 22 Jun 2008 14:02 |
| Last Modified: | 01 Nov 2019 14:00 |
| URI: | http://eprints.kfupm.edu.sa/id/eprint/10352 |