Single and multi-walled carbon nanotubes doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors

Abstract

Carbon nanotubes (CNTs) added polycrystalline (CNT)y(Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (y=0, 0.25%, 1.0% and 7%) superconductor samples have been synthesized at normal pressure. The X-ray diffraction (XRD) studies of these samples have shown an orthorhombic crystal structure following PMMM space group. The added CNTs have been found to diffuse at the inter-grain sites and act as cementing material. SEM images show that CNTs are forming an electrical-network between grains. These observations suggest that the CNT addition to the CuTl-1223 compounds improve the electrical connection between superconducting grains which in turn increase the Jc of the final compound. The room temperature resistivity of as-prepared samples decreases with the addition of CNT. The onset temperature of superconductivity [Tc(onset)] and zero resistivity critical temperature [Tc(R=0)] are found to decrease with the CNT additions. Except for the samples with CNT additions of 0.25%, the density [mass/volume] of final compound after CNT addition is decreased. Magnitude of diamagnetism is also suppressed with the addition of CNT which suggests that some of carbon atoms diffuse into the unit cells at the intra-grain sites. The Tc(R=0) becomes quite stable after post-annealing in oxygen atmosphere; the Tc(R=0) varies between 98 and 96K in polycrystalline (CNT)y(Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (y=0, 0.25%, 1.0% and 7%) samples. The out of phase component of magnetic susceptibility observed as a broad peak in the as-prepared samples, is transformed to a sharp peaks after post-annealing of the samples in oxygen atmosphere. This shows that oxygen diffusion converts the inter-grain material to respective oxides and carbonates that increase the surface areas of the current flow around inter-grain loops that reduce the hysteresis losses. The electron-microscopy of these samples has shown that inter-grain voids population is suppressed with the addition of CNTs. FTIR absorption measurements of (CNT)y(Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (y=0, 0.25%, 1.0% and 7%) samples have shown apical and planar oxygen modes at their usual positions.