Dr. Bernat Mundet defended his PhD thesis on “Atomic-scale characterization of structural distortions in perovskite oxide thin films”Monday, 9 October 2018, with great success, surrounded by his friends, family and colleagues! Congratulations!
Title: Atomic-scale characterization of structural distortions in perovskite oxide thin films
Date: Monday, 8 October 2018
Time: 4:30 pmVenue: Sala d’Actes Carles Miravitlles, ICMAB
Abstract: In this thesis, we investigate the structural distortions appearing in three different kind of perovskite oxides that are fabricated as thin films following a chemical solution deposition process. In the first case, we study how the YBCO lattice is distorted around its most common defect, this is the Y124 intergrowth. Secondly, we investigate which structural mechanisms help to accommodate the strain generated by the substrate mismatch in nickelate thin films. Finally, we study how the spatial confinement influences both the physical and structural properties of La0.7Sr0.3MnO3/SrTiO3 heterostructures.
Supervisor:
Jaume Gázquez, Superconducting Materials and Large Scale Nanostructures (ICMAB)
PhD Committee:
President: Francesca Peiró (UB)
Secretary: Felip Sandiumenge (ICMAB)
Vocal: César Magén (Instituto de Ciencia de Materiales de Aragón (ICMA))
On Monday, 24 September, this article appeared in the printed version in the newspaper “El Periódico”, both in the Spanish and Catalan version. The article is written by the journalist Valentina Raffio, and features our SUMAN researcher, Teresa Puig, in the framework of the project #LasCientíficasCuentan, an initiative by CSIC-Brussels and funded by the FECYT. We transcribe here the text.
Watch here the video of the ULTRASUPERTAPE project, the ERC Advanced Grant project awarded to Teresa Puig, explained here in plain words for everyone to understand!
The project “Las Científicas Cuentan” is an initiative of the CSIC Delegation in Brussels financed by the FECYT. The aim of the project is to bring basic science to the general public, through the story of women scientists who have been awarded with a ERC project during the past years. From SUMAN, Teresa Puig (ERC-Advanced Grant) participate in the project.
In this work we evaluate the defects and the associated distortions present in tensile and compressive-strained chemical solution deposition–derived NdNiO3 (NNO) and LaNiO3 (LNO) thin films by means of aberration corrected scanning transmission electron microscopy. We elucidate a fundamental link between strain and the most common defect observed in nickelate films, the Ruddlesden-Popper fault (RPF), which will ultimately impinge on the electrical properties of the films. Overall, the concentration of RPF defects increases with the lattice mismatch. More specifically, LNO films are always metallic, although transitioning from compressive to tensile strain results in the appearance of RPFs and an increase of the resistivity. On the other hand, NNO films always behave as insulators under tensile strain, whereas under compressive strain the increase of the thickness makes the onset of the metal-to-insulator transition shift to higher temperatures.
Flux magnetic relaxation (flux creep) causes logarithmic decay on the critical currents in superconductors, especially at high temperatures, in detriment of applications for high temperature superconductors. In this work, we present a novel methodology to measure the flux creep rate in YBCO from electrical transport measurements instead of using traditional magnetic relaxation measurements. This new methodology provides a faster way to analyze creep and enables to expand the analysis to any orientation of the magnetic field. In particular, we have applied this analysis to study the creep rate in chemical solution deposited nanocomposites (YBCO with included nanoparticles), revealing that emerging stacking faults provide flux pinning and additionally reduce the flux magnetic relaxation.
In-field angular pinning performances at different temperatures have been analysed on chemical solution deposited (CSD) YBa2Cu3O7−x (YBCO) pristine films and nanocomposites. We show that with this analysis we are able to quantify the vortex pinning strength and energies, associated with different kinds of natural and artificial pinning defects, acting as efficient pinning centres at different regions of the H–T phase diagram. A good quantification of the variety of pinning defects active at different temperatures and magnetic fields provides a unique tool to design the best vortex pinning landscape under different operating conditions. We have found that by artificially introducing a unique defect in the YBCO matrix, the stacking faults, we are able to modify three different contributions to vortex pinning (isotropic-strong, anisotropic-strong, and isotropic-weak). The isotropic-strong contribution, widely studied in CSD YBCO nanocomposites, is associated with nanostrained regions induced at the partial dislocations surrounding the stacking faults. Moreover, the stacking fault itself acts as a planar defect which provides a very effective anisotropic-strong pinning at H//ab. Finally, the large presence of Cu–O cluster vacancies found in the stacking faults have been revealed as a source of isotropic-weak pinning sites, very active at low temperatures and high fields.
Aquest dimecres 21 de Març a les 12.15 h, els companys de l’Associació Catalana d’estudiants de Física i l’ICMAB organitzen la conferència ‘LA SUPERCONDUCITIVTAT: Un fenòmen quàntic que està contribuint al canvi energètic’ a càrrec de la Prof. Teresa Puig ( a l’aula C3/022 de la Facultat de Ciències de la UAB)
Ligand-to-surface interactions are critical factors in surface and interface chemistry to control the mechanisms governing nanostructured colloidal suspensions. In particular, molecules containing carboxylate moieties (such as citrate anions) have been extensively investigated to stabilize metal, metal oxide, and metal fluoride nanoparticles. Using YF3 nanoparticles as a model system, we show here the self-assembly of citrate-stabilized nanostructures (supraparticles) with a size tunable by temperature. Results from several experimental techniques and molecular dynamics simulations show that the self-assembly of nanoparticles into supraparticles is due to ionic bridges between different nanoparticles. These interactions were caused by cations (e.g., ammonium) strongly adsorbed onto the nanoparticle surface that also interact strongly with nonbonded citrate anions, creating ionic bridges in solution between nanoparticles. Experimentally, we observe self-assembly of nanoparticles into supraparticles at 25 and 100 °C. Interestingly, at high temperatures (100 °C), this citrate-bridge self-assembly mechanism is more efficient, giving rise to larger supraparticles. At low temperatures (5 °C), this mechanism is not observed, and nanoparticles remain stable. Molecular dynamics simulations show that the free energy of a single citrate bridge between nanoparticles in solution is much larger than the thermal energy and in fact is much larger than typical adsorption free energies of ions on colloids. Summarizing our experiments and simulations, we identify as key aspects of the self-assembly mechanism the requirement of NPs with a surface able to adsorb anions and cations and the presence of multidentate ions in solution. This indicates that this new ion-mediated self-assembly mechanism is not specific of YF3 and citrate anions, as supported by preliminary experimental results in other systems.
Prof. Teresa Puig was invited to give a talk on superconducting materials at “Dissabtes de la Física” at Universitat Autònoma de Barcelona. More than 100 secondary school students listened to her talk, and then experienced the levitating phenomena with some members of her team
Dr. Bernat Mundet defended his PhD thesis on “Atomic-scale characterization of structural distortions in perovskite oxide thin films”Monday, 9 October 2018, with great success, surrounded by his friends, family and colleagues! Congratulations!
