14816

13333

كارشناسي ارشد

ماده چگال

اصفهان : دانشگاه صنعتي اصفهان

1397

يازده، 94ص.: مصور ، جدول، نمودار

1398/05/06

كتابنامه

فيزيك

فيزيك

1398/05/06

2550541

AbstractIn this research we study the effect of synthesis method on properties of YBCO superconduc tors and explore the effects of Mn Cr and Li substituions on the system Y1 x Mx Ba2 Cu3 O7 M Co Fe Cr Mn Li high Tc superconductors with different doping levels of x 0 0 004 0 01 and 0 02 were prepared by sol gel method In order to obtain an optimal sol gel methodfor the first time in our group and to compare the results with already synthesized solid state samples a pure sample along with previous dopings of Co and Fe were prepared Theobtained samples were examined by an AC susceptometer The magnetic susceptibility ofboth synthesis methods showed nearly identical profiles which shows the same transitiontemperature for both methods The optimal sol gel preparation method was used to studyMn Li and Cr substitutions for Y site In the quantum BCS theory phonon mediated elec tron pairing is introduced where magnetism opposes supercoductivity Considering thesetwo ideas Li with a high phonon frequency Mn and Cr magnetic ions were selected asdoping elements Magnetic susceptibility critical current density XRD and SEM data werecollected for the samples XRD results indicate that all samples are single phased and areformed in orthorhombic 123 crystal structure Also the samples showed very high criticalcurrent density Jc values compared to solid state samples which means the Jc values arehighly dependent on the synthesis method AC magnetic susceptibility measurments showedslightly decreased transition temperatures in Mn Li and Cr doped samples Critical densityvalues are highly dependent on the synthesis method In brief we believe these result arethe first observation of which cuprate superconductors follow and obey the spin fluctuationmodel for pairtin Keywords YBCO high Tc superconductor magnetic sysceptibility critical current den sity sol gel method

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