Interplanar Coupling and Superconductivity in (Cu½TI½)Ba2(Ca2-xKx )Cu3O10-δ (x=0, 0.5, 1, 1.5) Samples

Abstract

High-temperature superconductors (HTSC) is one of the most studied materials over the past century. The most noticeable family of the HTSC is the Tl-Ba-Ca-Cu-O cuprate family. There were many compounds prepared under this family of superconductors and still we are working on this compound. To further elaborate on the importance of this superconductor family we have doped alkali metal (Potassium) in this compound at Calcium sites by synthesizing (Cu1/2Tl1/2)Ba2(Ca2-xKx)Cu3O10-δ(x=0, 0.5, 1, 1.5) superconducting samples. The samples were then characterized by X-ray diffraction, four-probe resistivity, scanning electron microscopy (SEM), and FTIR absorption measurements. These samples have shown high crystalline structure and followed the orthorhombic crystal and Pmmm space group. We found out that Potassium doping causes an initial increase in the c-axis length and unit cell volume, which is followed by a subsequent decrease as K doping is increased to 50%.This behavior is due to less electronegativity of K compared to Ca atoms. A subsequent decrease in the Tc(R=0K) and the Tc (onset) with the doping of potassium was observed which is due to the weaker interplanar coupling caused by doping of larger ionic size K atom compared to Ca. The apical oxygen mode of type Cu(1)-OA-Cu(2) is softened with the doping of K in the final compound, as observed in the FTIR absorption measurements. Likely due to the increase in the c axis that takes place in the charge reservoir layer blocks which elongates the bond length of Cu(1)-OA-Cu(2) and hence the softening of this apical oxygen mode. The coherence length along the c-axis ξc(0), and the London penetration depth λp.d increase after doping of potassium and keep increasing as we increase the doping concentration of potassium. From here we can say the doping of the K at the Ca site the thickness of the interplanar layers increases thereby making the efficient transfer of the charge carriers to the conducting planes and hence increasing the density of the charge carrier in the conducting CuO2 planes. The values of parameters such as Bc0(T), Bc1(T), Jc(0) are decreased with the increased K doping. This is because a smaller sized K causes the healing effect which reduces the microscopic pinning centers. We came to the conclusion that any alteration in the unit cell structure atom’s mass or electronegativity with doping will significantly disrupt the interplanar coupling