Enhancing Superconductivity in Low Dimensional TlBa2Ca2Cu3O10−δ System

Abstract

Mg doped Tl(Ba2-xMgx)(Ca2-yBey)Cu3O10-δ (y=0; x=0, 0.25, 0.50, 0.75, 1.0, 1.25,1.5) and Tl(Ba2-xMgx)(Ca1Be1)Cu3O10-δ (x=0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.50, 1.75) superconductors are synthesized at the normal pressure and the possible mechanism of superconductivity in these compounds is studied. Tl(Ba2-xMgx)(Ca2-yBey)Cu3O10-δ (y=0) samples have shown an orthorhombic crystal structure and their c-axes length decreases up to Mg-doping of x=0.75 and then increases up to Mg-doping of x=1.50. The c-axes length in Tl(Ba2-xMgx)(Ca1Be1)Cu3O10-δ samples, however, decreases up to a Mg-doping of x=1.25 and then increases for Mg-doping of x=1.5. 1.75. In these studies we have investigated the role of decreased thickness of charge reservoir layer on the mechanism of superconductivity. The Tc(R=0) in as-prepared Tl(Ba2-xMgx)(Ca2-yBey)Cu3O10-δ (y=0; x=0, 0.25, 0.5, 0.75, 1.0, 1.25) samples was 100, 98, 101, 102, 100, 96K and in the oxygen post-annealed Tc(R=0) is observed around 99, 98, 108, 127, 109, 97K, respectively. However, in as-prepared Tl(Ba2-xMgx)(Ca1Be1)Cu3O10-δ (x=0.25, 0.5, 0.75, 1.0, 1.25, 1.50) samples the Tc(R=0) is observed around 97, 99, 100, 94, 92, 93, 91K and in oxygen post-annealed samples the Tc(R=0) is observed at 100, 98, 103, 101, 100, 99, 99K, respectively. The magnitude of the superconductivity after Mg-doping is improved in Tl(Ba2-xMgx)(Ca2-yBey)Cu3O10-δ (y=0; x=0.25, 0.5, 0.75, 1.0, 1.25) and Tl(Ba2-xMgx)(Ca1Be1)Cu3O10-δ (x=0.25, 0.5, 0.75, 1.0, 1.25, 1.50) samples. It was observed from the FTIR absorption measurements that the phonon modes related to CuO2 planar oxygen atoms are hardened with the doping of Mg in the charge reservoir layer. These studies have shown that the thickness of charge reservoir layers decreases with Mg-doping which most likely makes charge transfer mechanism more efficient that increases in the magnitude of superconductivity in the final compound.