Superior pinning properties in nano-engineered YBa2Cu3O7-δ

Abstract

Large electrical current transport in the absence of energy losses is the key factor in commercial applications of high temperature superconductors. This thesis demonstrates an easy and inexpensive bottom-up technique to produce self assembled nanorods, segmented nanorods as well as nanoparticles in YBa2Cu3O7-δ thin films grown by pulsed laser deposition. The structural and morphological characteristic of the pinning landscapes produced are investigated and correlated to their effects on the superconducting properties of the thin films. In particular two pinning landscapes are investigated: Ba2YNbO6 nanorods are grown in YBa2Cu3O7-δ thin films using a Ba2YNbO6 doped YBa2Cu3O7-δ pulsed laser deposition targets and Ba2(Y/Gd)(Nb/Ta)O6 segmented nanorods together with (Y/Gd)2O3 nanoparticles are grown in (Y/Gd)Ba2Cu3O7-δ thin films using a Ba2YNbO6 + Gd3TaO7 doped YBa2Cu3O7-δ pulsed laser deposition targets. The Ba2YNbO6 + YBa2Cu3O7-δ is deeply characterised and the effects of the deposition parameters are analysed. Ba2YNbO6 is demonstrated to be an interesting novel pinning addition capable to increase the critical current and to reduce the YBa2Cu3O7-δ critical currents angular dependencies anisotropy. The Ba2YNbO6 + Gd3TaO7 + YBa2Cu3O7-δ is found to produce a new complex pinning landscape extremely effective. At high fields the synergetic combination of the different defects typology is shown to generate an interesting new feature in the critical current angular dependencies. Chapter 1 is an introduction to superconductivity, the fundamentals of the field are briefly presented. In chapter 2 the discussion in focused on pinning in high temperature superconductors. Cuprates and in particular YBa2Cu3O7-δ are presented. The pinning phenomenon and the practical pinning engineering in thin films is also discussed in this chapter. Chapter 3 describes the thin films preparation methods and the characterisation techniques used in the research work. Chapter 4 and 5 are focused on the Ba2YNbO6 doped YBa2Cu3O7-δ thin films. Chapter 4 is an introduction to Ba2YNbO6 doped YBa2Cu3O7-δ, the preliminary results obtained on Ba2YNbO6 doped YBa2Cu3O7-δ thin films are shown in this chapter. The crystalline structure, the morphology and the superconducting properties of thin films deposited adopting different deposition parameters are analysed and discussed in chapter 5. In chapter 6 the new complex pinning landscape of Ba2(Y/Gd)(Nb/Ta)O6 and (Y/Gd)2O3 in (Y/Gd)Ba2Cu3O7-δ is presented. Concluding remarks on the research described in the work ends the thesis in a brief final chapter 7.