A study on the superconducting properties of YBa2Cu3-xNbxO7-y (x=0 to 1) thin films

Effect of Nb substitution at the copper site in YBa2CuxO1-x (Y-123) was studied in thin film form. Stoichiometric targets of YBa2Cu1-xNbxO7-y (YBCNO) where x=0 to 1 were used and thin films were made on SrTiOy<100> substrate by using pulsed laser deposition (PLD) method. XRD studies have shown that the films are strongly c-axis oriented in nature. For x>0.1YBa2NbO6 becomes detectable and its intensity increases with x. Tc was found to decrease from 89 K to 82 K and C-axis parameter found to increase with the increase in x. For x>0.4 no superconductivity was observed. However, an increase in Jc was observed up to x≤0.05 in YBCNO films. The best Jcs realized for x=0.0, 0.025 and 0.05 are 1.40cdot106 A/cm2 at 77 K, respectively. The improvement in Jc for small concentrations of Nb substitution can be attributed to changes in microstructure with improved grain size and aligned grains. (orig.)