12291

11259

كارشناسي ارشد

ماده چگال

اصفهان: دانشگاه صنعتي اصفان، دانشكده فيزيك

1395

شش، 114ص.: مصور، جدول، نمودار

ص. ع. به فارسي و انگليسي

حميده شاكري پور

هادي سلامتي

محمد اخوان، پرويز كاملي

1395/12/18

كتابنامه

فيزيك

فيزيك

ID11259

Abstract In this thesis high temperature superconducting Y1 x F ex Ba2 Cu3 O7 samples with 0 x 0 1 wereprepared by the conventional solid state reaction The X ray diffraction pattern analysis shows that all thesamples are single phase up to x 0 1 and no impurity phases are detected All samples have an orthorhombicstructure with Pmmm symmetry Lattice parameters and unit cell volume of samples were determinedby Rietveld refinement method which indicate an increase in the lattice parameter c with increasing Feconcentration up to 0 4 Also in plane Cu 2 O 2 bond lengths were found to be decreasing withincreasing Fe doping up to an optimal concentration of 0 004 In other words the CuO2 planes become moredistorted and hence charge carriers may have better chances of transportation so it can be considered as anevidence for the increasing Tc up to the optimal doping level By increasing the Fe doping concentration tomore than the optimal level the Cu 2 O 2 bond lengths start to increase and cause CuO2 planes to flatten The flattening of CuO2 planes is attributed to the decrease in the transition temperature The real part ofmagnetic susceptibility versus temperature shows sharp drops from normal to diamagnetic superconductingstate which is due to intra grain transition By analyzing the susceptibility data it is evident that thesuperconducting transition temperature increases up to the optimal doping level and then starts to decreaseas the doping concentration increases The observed variations of Tc can also be detected in the imaginarypart of the magnetic susceptibility curves Furthermore the peak position of the imaginary part starts to rise resulting in sharper peaks as the doping concentration is increased to the optimal value The increased peakpositions are signatures of enhanced flux pinning up to the optimal doping By increasing the doping level the imaginary peaks show lower and wider peaks which means that the flux pinning is affected negatively The electrical resistivity measurements show nearly linear temperature dependence in the normal state Thenormal state resistivity of the samples decrease with increasing Fe content up to the optimal concentration and then it increases as the doping level is increased Increasing of transition temperature with increasingFe content in the Y site up to an optimal value is also confirmed by the electrical resistivity transitiontemperatures and is clearly inconsistent with the Abrikosov Gorkov theory keywords Y1 x F ex Ba2 Cu3 O7 superconductivity Fe ion superconducting transition temperature

حميده شاكري پور

هادي سلامتي

محمد اخوان، پرويز كاملي