Pulsed laser deposition of La1.5Dy0.5CaBa2Cu5Oz superconducting thin films

Full text: The La and Ca substituted, tetragonal superconductors have enhanced corrosion resistance compared to RE-123 type orthorhombic superconductors. These tetragonal superconductors have a stable oxygen stoichiometry and structure with lesser aging effect in the atmosphere compared to the orthorhombic RE-123 superconductors. This property of tetragonal superconductors, particularly La-Ca substituted systems, is desirable for possible thin film applications. A single-phase target of polycrystalline La1.5Dy0.5CaBa2Cu5Oz (La-2125) was used for the deposition of thin films pulsed laser deposition technique. A KrF excimer laser (λ = 248 nm) with pulse repetition rate of 10 Hz, energy density of 0.9 J/cm2 on the target, the substrate-target distance of 4.5 cm distance was used to deposit the La-2125 thin films (∼2000 A) on single crystal LaAlO3 (001) substrates held at temperature of 820 deg C. The O2 partial pressure in the chamber was maintained at 500 mTorr during the deposition. The XRD patterns showed that the thin films were pure phase (La-2125) and c-axis oriented on single crystal LaAlO3 (001) substrates. The resistance was measured as a function of temperature for determining the Tc of the thin films. The films showed the onset of superconducting transition at ∼79 K and the Tc ∼ 75 K, which is close to the Tc (∼ 78 K) of single-phase bulk La-2125 compound. Recent irradiation studies on the La-2125 thin films using Ag and O beams have shown that the columnar defects created by the ion beams of certain fluence (ions.cm2) have desirable effect on the critical current density, i.e., up to certain fluence Jc increases with increasing fluence. The typical Jc for pristine and irradiated thin film of La-2125 composition is of the order of 106 A/cm2. The irradiation results in two or three fold increase in the Jc value. In this presentation, we will highlight the results of ERDA experiments and effect of ion-beam irradiation on the modification of superconducting properties of La-2125 thin films