اثر آلايش عنصر مغناطيسي كبالت بر خواص ابررساناي Y1-xCoxBa2Cu3O7-δ

چكيده انگليسي :

84Abstract In this thesis high temperature superconductors Y1 xCoxBa2Cu3O7 samples with 0 0 07 were prepared by the conventional solid state reaction The x ray diffractionpattern analysis shows that all the samples until x 0 008 were single phase and no impurityphases are detected by increasing of doping from x 0 008 the BaCuO2 impurity phase isdetected in samples that its uncreasing by enhancing the dopping content All samples havean orthorhombic structure with pmmm symmetry Lattice parameters and unit cell volumeof samples were found by Rietveld method and it shows that lattice parameter c increaseswith increasing Co also in plane Cu 2 O 2 bond length were found by Rietveld methodand it is seen that Cu 2 O 2 bond length decrease with increasing Co up to optimal contentof 0 02 in the other word CuO2 planes become charge carriers have better chances fortransfering so it can be strong evidence for increasing of transition temperature yp to thisconcentration By increasing concentration from optimal content 0 02 Cu 2 O 2 bondlength starts to increase It shows that CuO2 planes become flat and this describes decreasingof transition temperature by increasing of concentration after 0 02 the real part of magneticsusceptibility versus samples temperature shows sharp drop from normal state todiamagnetic superconducting state that it s because of in grain transtion By anlaysing ofsusceptibility data we see that by increasing of magnetic element of Co till 2 doping thetransition temperature of superconductivity increases That increasing of holes bysubstitution of Co with oxidation of 2 and 3 in the place of Y with 3 oxidation can bethe reason for icreasing in transition temperature Then by increasing of dopingconcentration transition temperature starts to decrease that overdoping of holesconcentration after x 0 02 can be the reason of this deacrising of transition temperature Also this increasing of transition temperature till 0 02 and then deacrising of transitiontemperature can be seen in imaginary part of magnetic susceptibilty curve Also altitude ofimaginary peaks in susceptibility curve increase by increasing Co till 0 03 that it show theinhancement of flux pinning up to 0 03 then by decreasing of altitude and width of peaksafter x 0 03 flux pinning become decrease The electrical resistivity show nearly lineartemperature dependence in the normal state and by increasing of Co content it shows a bettermetallic behavior and resistivity of samples deacrese till 0 02 by increasing of dopingconcentration resistivity increases Electrical resistivity curve shows an increase in transitiontemperature till 0 02 and then by increasing of Co critical temperature decrease Increasingof transition temperature with increasing of Co element in Y site till an optimal concentrationis in contradiction with Abrikasov Gorkov theory Critical current density were measuredfor different doping concentration It shows that critical current density increase till x 0 03and it gets to it s higher point at x 0 03 and by increasing the doping content after this critical current density starts to decrease and it gets to its minimum point at x 0 07 it seemsthat cobalt element acts like center of flux pinning in compound and improves the criticalcurrent density Keywords superconductivity magnetic susceptibility electrical resistivity critical currentdensity

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اثر آلايش عنصر مغناطيسي كبالت بر خواص ابررساناي Y1-xCoxBa2Cu3O7-δ

پذيرفتاري مغناطيسي , مقاومت الكتريكي , چگالي جريان بحراني