Liquid-assisted ultrafast growth of superconducting films derived from chemical solutions
- Autores: Laia Soler Bru
- Directores de la Tesis: Susagna Ricart Miró (dir. tes.), Xavier Obradors Berenguer (dir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2019
- Idioma: español
- Tribunal Calificador de la Tesis: Juan Manuel García Ruiz (presid.), Felip Sandiumenge Ortiz (secret.), Bartlomiej Andrezej Glowacki (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia de Materiales por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
The widespread use of High Temperature Superconductors (HTS) into large scale applications is, in part, still limited by the high costs of coated conductors manufacturing. Aiming for a breakthrough to achieve high throughput, in this thesis we have developed a novel technique that combines the low cost benefits of Chemical Solution Deposition (CSD) with the very high growth rates of crystallization from liquid phases. It relies on the formation of a transient liquid derived from carboxylate solutions, taking advantage of the kinetic hindrances on crystallization to reach the equilibrium phase.
In this dissertation, we first explain the basics of the process that leads to YBa2Cu3O7-δ crystallization assisted by a transient liquid and then we elaborate on the results of our investigation about this technique. The “proof-of-principle” of this new approximation viability has been achieved with the use of rapid thermal annealing furnaces, allowing heating rates up to 80ºC/s.
The reactions involved in the process are observed with in situ measurements and microscopic analyses, among others. First, the pyrolysis of the Ba, Cu and Y propionates mixture at low temperatures (500ºC) is observed with in situ infrared spectroscopy. Then, time resolved X-ray diffraction with synchrotron light is used to reveal the reaction paths to convert the resulting BaCO3, CuO and Y2O3 to the final phase, as well as nucleation and growth of the YBa2Cu3O7-δ film from the transient liquid.
To do so, the deposition step is performed with spin coating or Ink Jet printing methodologies. The solutions characteristics have been adapted to the deposition technique and correlated to the resulting film morphology.
Then, several parameters have been investigated to control the rate limiting BaCO3, elimination reaction in order to avoid carbon retention in the final thick epitaxial films.
Afterwards, the basic concepts for understanding the nucleation and growth mechanisms of YBCO with TLAG are set. With the aim of obtaining c-axis epitaxial YBa2Cu3O7-δ films, several strategies are presented to control the driving force for crystallization. The relevant parameters are solution composition, oxygen pressure, heating ramps and growth temperatures. Finally, the crystallization conditions are correlated to the resulting films microstructure and superconducting performances.
Two different paths are presented to reach TLAG. A direct temperature raise at constant oxygen pressure (Temperature-route), or a two step process (pO2-route). For the latter, BaCO3 elimination is disentangled from YBa2Cu3O7-δ growth by a jump on pO2.
Additionally, several challenges needed to be addressed depending on the route: liquid reactivity with the substrates due to its highly corrosive nature or improper wettability, are some of them.
Finally, we have succeeded in obtaining highly epitaxial YBCO thin films of 90-500nm with very high superconducting performances (Tc 90-92K, Jc up to 5MA/cm2 at self-field and 77K), at growth rates up to 100nm/s, increased by a factor 100 from those reported with conventional CSD. This methodology could be applied to other materials.
