Investigating the impact of CNTs addition on superconducting and dielectric properties of Cu1/2Tl1/2-1234 superconductors

Carbon nanotubes (CNTs) added Cu 1/2 Tl 1/2 -1234 superconducting composites were synthesized at 900 °C by two-step solid-state reaction method. The effect of CNTs additions on the superconducting and dielectric properties is studied for these materials. All the samples have shown orthorhombic crystal structure in which the c-axis length and the unit cell volume decrease with the addition of CNTs indicating the partial diffusion of carbon from the CNTs into the Cu 1/2 Tl 1/2 -1234 unit cell from the inter-grain sites. Suppression in the Tc(onset) and the Tc is observed with the increased concentration of CNTs addition. The apical oxygen phonon mode of type Cu (2) -O A -Cu (1) is hardened by CNTs additions showing that some carbon from the CNTs is incorporated into the unit cell. In the frequency-dependent dielectric measurements the real (ε r ) and imaginary (ε i ) part of the dielectric constants are suppressed with the increase of applied frequency, but their absolute values rise as the measuring temperature is decreased. The inclusion of CNTs in the final product also results in a suppression of the absolute values of the dielectric constants when compared to the pure samples. The dielectric measurements also confirm that the carbon from the CNTs partially diffuse into the unit cells, thereby promoting the suppression of dielectric constant. On the other hand, the diffused carbon atoms in the unit cell act as efficient pinning centres.