Salleh, Zulzamri (2008) Effects of TA substitution and addition of NANO-MgO particles on formation and superconductivity of TlSrl212 ceramics / Zulzamri Salleh. Masters thesis, Universiti Teknologi MARA.
In this work, the effect of tantalum (Ta) substitutions at the Sr-site on superconductivity of Tlo.9Bio.iSr2-^TaxCao.9Yo.iCu207 (x = 0 - 0.40) series and the effect of nanosize MgO particles on 1212 phase formation and transport critical current density, Jc in external magnetic field for Tlo.9Bio.iSri.95Tao.o5Cao.9Yo.iCu207 + >>MgO (y = 0 - 0.8 wt.%) series and Tlo.5Pbo.5Sri.gYbo.2CaCu207 + zMgO (z = 0 - 0.80 wt.%) series superconductors were investigated. Results of tantalum substitution at Sr-site in Tlo.9Bio.1Sr2-xTaxCao.9Y0.iCu207 (x = 0 - 0.40) series showed that the best superconducting behavior occurred at x = 0.05 with Tc<mse[of 96 K and Tczero of 65 K. Higher Ta substitution caused gradual deterioration of superconductivity, accompanied by a change of normal state behavior from metallic to semiconductor-like behavior with increasing Ta. SEM investigation showed changes in grain size with Ta substitution. Results of electrical measurements on Tlo^Bio.iSri.gsTao.osCao^Yo.iC^O? +jMgO (y = 0 - 0.8 wt.%) series superconductor revealed the highest transport critical current density Jc (at 20 K) of 28 A/cm2 aty = 0.2 wt.%. Samples withy = 0 - 0.40 wt.% showed a rapid drop of Jc at low fields (< 0.1 Tesla) before a slower deterioration at higher fields (> 0.1 Tesla). This indicates the presence of weak links at low fields and dominance of strong links at higher fields. The smallest drop of Jc was observed for sample y = 0.2 wt.%. SEM results for these series showed no significant difference in microstructure between MgO added samples. Results of electrical measurements on Tlo.sPbo.sSri.gYbo^CaQ^O? +zMgO (z = 0 - 0.80 wt.%) series revealed the highest Jc (at 30 K) of 16 A/cm2 for z = 0.1wt.%. The behavior of Jc in external fields also indicates presence of weak links at low fields. The smallest drop of Jc was observed for z = 0.1 wt.%. SEM micrographs of MgO added samples showed smaller grain size compared to pure samples. The enhanced Jc at y = 0.2 wt.% for the Tlo^Bio.iSn^Tao.osCao^Yo.iC^O? +^MgO series and z = 0.1 wt.% for the Tlo.5Pbo.5Sri.gYbo.2CaCu207 + zMgO series is suggested to be due to flux pinning as a result of the MgO additions. In conclusion, substitution of Tao.05 at Sr-site successfully stabilized the 1212-phase during synthesis of Tl 1212 superconductors. The addition of a moderate amount of nano-MgO particle before final sintering improved transport critical current density and enhanced flux pinning ability of the Tl-1212 superconductors.
|Subjects:||Q Science > QC Physics > Electricity and magnetism|
|Divisions:||Faculty of Applied Sciences|
|Depositing User:||Pn. Zuhaslinda Sulaiman|
|Date Deposited:||13 Jul 2012 03:23|
|Last Modified:||13 Jul 2012 03:23|