Superconductivity in Co doped Cu0.5Tl0.5Ba2(CaM)Cu2.95Co0.05O10-δ (M = Mg, Be) samples

We have investigated the possible source of suppression of superconductivity in Cu0.5Tl0.5Ba2Ca2Cu2.95Co0.05O10-delta samples. We substituted Mg (r = 0.65 angstrom) and Be (r = 0.31 angstrom) at Ca (r = 0.99 angstrom) sites in Cu0.5Tl0.5Ba2CaMCu2.95Co0.05O10-delta (M = Mg, Be) superconductor to enhance inter-planar coupling and Li in the charge reservoir layer (Cu0.5Tl0.25Li0.25)Ba2O4-delta to supply extra carriers to CuO2 planes. It was observed that zero resistivity critical temperature is decreased after Mg and Be substitution in Cu0.5Tl0.5Ba2CaMCu2.95Co0.05O10-delta samples. However, the c-axis lattice parameter is increased in both samples in spite of smaller ionic radius of Mg and Be as compared to Ca. However, in Cu0.5Tl0.5Ba2CaMCu2.95Co0.05O10-delta (M = Mg, Be) samples we have achieved enhanced superconductivity by Li doping. It was observed from these studies that cobalt doped in the conducting CuO2 planes somehow localizes the carriers at Co3+ sites and decrease the density of mobile carriers. But Li in Cu0.5Tl0.5Ba2O4-delta charge reservoir layer supplies the required number of carriers to the CuO2 planes; therefore, the critical temperature is increased in Li doped samples. (C) 2009 Elsevier B.V. All rights reserved.