Superconductivity in Co doped Cu 0.5Tl 0.5Ba 2(CaM)Cu 2.95Co 0.05O 10− δ (M = Mg, Be) samples

Abstract

We have investigated the possible source of suppression of superconductivity in Cu 0.5Tl 0.5Ba 2Ca 2Cu 2.95Co 0.05O 10− δ samples. We substituted Mg ( r = 0.65 Å) and Be ( r = 0.31 Å) at Ca ( r = 0.99 Å) sites in Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ (M = Mg, Be) superconductor to enhance inter-planar coupling and Li in the charge reservoir layer (Cu 0.5Tl 0.25Li 0.25)Ba 2O 4− δ to supply extra carriers to CuO 2 planes. It was observed that zero resistivity critical temperature is decreased after Mg and Be substitution in Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ 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 Cu 0.5Tl 0.5Ba 2CaMCu 2.95Co 0.05O 10− δ (M = Mg, Be) samples we have achieved enhanced superconductivity by Li doping. It was observed from these studies that cobalt doped in the conducting CuO 2 planes somehow localizes the carriers at Co 3+ sites and decrease the density of mobile carriers. But Li in Cu 0.5Tl 0.5Ba 2O 4− δ charge reservoir layer supplies the required number of carriers to the CuO 2 planes; therefore, the critical temperature is increased in Li doped samples.