Suppression of Tc in Co-doped (Cu0.5Tl0.5)Ba2Ca2Cu3−xCoxO10−δ superconductor

The most possible sources of suppression of superconducting properties (i.e., zero resistivity Tc(R = 0), magnitude of diamagnetism, etc.) in cobalt-doped (Cu0.5Tl0.5)Ba2Ca2Cu3−xCoxO10−δ (x = 0, 0.05, 0.1, 0.5) superconductor have been explored. It has been observed from these studies that Co-doping at Cu2+ sites in the CuO2 planes somehow localizes the carriers at Co3+ sites and decreases the density of mobile carriers in the superconducting CuO2 planes. We doped Li at Tl sites in Cu0.5Tl0.5Ba2O4−δ charge reservoir to obtain an efficient carriers doping (Cu0.5Tl0.25Li0.25)Ba2O4−δ charge reservoir layer of (Cu0.5Tl0.25Li0.25)Ba2Ca2Cu3−xCoxO10−δ compound to replenish the density of mobile carriers in the CuO2 planes; since alkali metals are known to lose their outermost “s-orbital” electron easily, which can be supplied to the superconducting CuO2 planes. The increased free carrier density in the superconducting CuO2 planes enhances the superconducting properties of the final compound.

Research highlights▶ The localization of these carriers is a source suppression of superconductivity as observed from the lowering of Tc(0) in (Cu0.5Tl0.5)Ba2Ca2Cu3−xCoxO10−δ samples or it may also be due to hole filling in CuO2 planes. However, the localization of carriers can be compensated if more carriers are supplied to CuO2 planes. The Li-doping at Tl sites in the (Cu0.5Tl0.25Li0.25)Ba2O4−δ charge reservoir layer of (Cu0.5Tl0.25Li0.25)Ba2Ca2Cu2.5Co0.5O10−δ has been found to enhance the superconducting properties. The substitution of Li has provided a sufficient number of mobile carriers to CuO2 planes required for superconductivity at higher critical temperature. These observations have shown that the magnetic impurity Co3+ has developed localization of the carriers at its sites in the CuO2 planes or it may also be due to hole filling in CuO2 planes and hence due to deficiency of mobile carriers, the superconductivity has been suppressed in Co-doped (Cu0.5Tl0.5)Ba2Ca2Cu3−xCoxO10−δ superconductor.