Influence of Ti doping on the superconducting properties of YBa2(Cu3−xTix)O7−δ materials

Abstract

YBa2(Cu3−xTix)O7−δ (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) superconductors are synthesized at 900 °C by solid state reaction method. The superconducting properties of the samples are studied by X-ray diffraction, resistivity, AC-susceptibility and Fourier transform infrared spectroscopy (FTIR) absorption measurements. These samples have shown orthorhombic crystal structure and the cell parameters slightly increase for higher Ti-contents. The Tc(R = 0), the onset temperature and magnitude of diamagnetism are suppressed with increasing Ti-doping. A new in-chain [Ti–O–Cu(1)] oxygen vibration mode appears around 551 cm−1 in the FTIR spectra which grows in intensity with increased Ti-doping. The peak position of the CuO2 planar oxygen mode is not affected with the doping of Ti showing that Ti is doped at the in-chain-copper Cu(1) sites in the unit cell. The fluctuation induced conductivity analyses reveals that despite an increase in the parameters such as ξc, VF, and inter-layer coupling J, the critical temperature and superconductor volume fraction are suppressed. It shows that the doped Ti-atoms most likely induce anharmonic oscillations which may suppress the density of phonon population and hence the superconductivity. It can also be witnessed in the decreased phase relaxation time of the carriers with increasing Ti-doping. These studies stress on the essential role of soft phonons in the mechanism of high Tc superconductivity in YBa2(Cu3−xTix)O7−δ superconductors.