Superconducting Properties of K-doped Cu0.5Tl0.5-1223 samples

Abstract

Cu0.5Tl0.5Ba2Ca2Cu3-xKxO10-δ (x=0, 1, 2, 2.5, 3) and Tl1.0Ba2Ca2K3O10-δ samples have been prepared by two step solid state reaction method for the investigation role of excess free electrons at room temperature in the electron CuO2 plane and their effect on the process of high Tc superconductivity in the superconducting state. The samples are characterized by x-ray diffraction (XRD), resistivity (RT) and Fourier Transform Infrared (FTIR) absorption measurements. The crystal structure of all the samples is drawn by using the experimentally determined cell parameters and by fitting them via a software ”VESTA” computer program. In the resistivity measurements all samples have shown metallic variations of resistivity from room temperature down to onset of superconductivity with zero resistivity critical temperature around 93K. In TlBa2Ca2K3O10-δ samples have displayed variable range-hopping conductivity and semiconducting behavior with an energy gap of 3.28 meV.; in such samples copper Cu (3d9) atom is entirely eliminated from charge reservoir layer (CRL, i.e Tl1.0Ba2O4-δ charge reservoir layer). These observations have clearly shown that spin containing Cu (3d9) atoms are essential for mechanism of high Tc superconductivity; since enough free carriers were available via alkali metal at room temperature in the CuO2 planes. The apical oxygen modes of type Tl-OA-Cu (2) and Cu(1)-OA-Cu(2) are hardened with the doping of K at CuO2 planar sites showing intrinsic evidence of doping of K atoms in the final compound. Enhancement in the values of coherence length along the c-axis ξc(0), the inter-layer coupling J and VF (the Fermi velocity) of superconducting carriers and the energy required to disassemble the Cooper-pairs is observed with the doping of K in the final compound. The enhancement in the values of these parameters most likely arises from the increased density of free carriers provided by doped alkali atoms. Most likely, the extra free carriers supplied by doped alkali atoms to the conducting CuO2 planes at room temperature increase electron-hole recombination processes and help the carriers that bring them to an ideal level.