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.The work described in this dissertetion was supported by NESPA, Nano-Engineered Superconductors for Power Application, a framework of the Marie Curie Research Training Network, funded within the EUs 6th framework program