Coated Conductor technology for the beamscreen chamber of future high energy circular colliders

Teresa Puig, Patrick Krkotic, Artur Romanov, Joan O’Callaghan, Danilo Andrea Zanin, Holger Neupert, Pedro Costa Pinto, Pierre Demolon, Ângelo Rafael Granadeiro Costa, Mauro Taborelli, Francis Perez, Montse Pont, Joffre Gutierrez and Sergio Calatroni. Superconductor Science and Technology

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Band Gap Tuning of Solution-Processed Ferroelectric Perovskite BiFe1–xCoxO3 Thin Films

Pamela MachadoMateusz ScigajJaume GazquezEstel RuedaAntonio Sánchez-DíazIgnasi FinaMartí Gibert-RocaTeresa PuigXavier ObradorsMariano Campoy-Quiles, and Mariona Coll*Chem. Mater.201931 (3), pp 947–954  DOI: 10.1021/acs.chemmater.8b04380

Ferroelectric perovskite oxides are emerging as a promising photoactive layer for photovoltaic applications because of their very high stability and their alternative ferroelectricity-related mechanism for solar energy conversion that could lead to extraordinarily high efficiencies. One of the biggest challenges so far is to reduce their band gap toward the visible region while simultaneously retaining ferroelectricity. To address these two issues, herein an elemental composition engineering of BiFeO3 is performed by substituting Fe by Co cations, as a means to tune the characteristics of the transition metal–oxygen bond. We demonstrate by solution processing the formation of epitaxial, pure phase, and stable BiFe1–xCoxO3 thin films for x ≤ 0.3 and film thickness up to 100 nm. Importantly, the band gap can be tuned from 2.7 to 2.3 eV upon cobalt substitution while simultaneously enhancing ferroelectricity. As a proof of concept, nonoptimized vertical devices have been fabricated and, reassuringly, the electrical photoresponse in the visible region of the Co-substituted phase is improved with respect to the unsubstituted oxide.

Faceted‐Charge Patchy LnF3 Nanocrystals with a Selective Solvent Interaction

Martínez‐Esaín, J. , Puig, T. , Obradors, X. , Ros, J. , Yáñez, R. , Faraudo, J. and Ricart, S. (2018)  Angew. Chem. Int. Ed.

doi:10.1002/anie.201806273

A fast and single‐step preparation of patchy LnF3 faceted‐charge nanocrystals are described. These hexagonal faceted nanocrystals allow the spontaneous selective adsorption of cations or anions in the different faces, producing stable and well‐defined patches of different charge. The mechanism for the formation of the patches and the properties of the obtained nanocrystals were characterized by a combination of experimental techniques and all‐atomic molecular dynamics simulations. The spontaneous dual‐charged surface as well as the luminescence effects that can be achieved by doping host–LaF3 systems make these new nanocrystals interesting both from a fundamental point of view and for a wide range of applications.

Electrochemical Tuning of Metal Insulator Transition and Nonvolatile Resistive Switching in Superconducting Films

Anna Palau*,Alejandro Fernandez-RodriguezJuan Carlos Gonzalez-RosilloXavier GranadosMariona CollBernat BozzoRafael Ortega-HernandezJordi SuñéNarcís MestresXavier Obradors, and Teresa Puig. ACS Appl. Mater. Interfaces, 2018, 10 (36), pp 30522–30531.

DOI: 10.1021/acsami.8b08042

Modulation of carrier concentration in strongly correlated oxides offers the unique opportunity to induce different phases in the same material, which dramatically change their physical properties, providing novel concepts in oxide electronic devices with engineered functionalities. This work reports on the electric manipulation of the superconducting to insulator phase transition in YBa2Cu3O7−δ thin films by electrochemical oxygen doping. Both normal state resistance and the superconducting critical temperature can be reversibly manipulated in confined active volumes of the film by gate-tunable oxygen diffusion. Vertical and lateral oxygen mobility may be finely modulated, at the micro- and nano-scale, by tuning the applied bias voltage and operating temperature thus providing the basis for the design of homogeneous and flexible transistor-like devices with loss-less superconducting drain–source channels. We analyze the experimental results in light of a theoretical model, which incorporates thermally activated and electrically driven volume oxygen diffusion.

Direct and Converse Piezoelectric Responses at the Nanoscale from Epitaxial BiFeO3 Thin Films Grown by Polymer Assisted Deposition

DOI:10.1039/C8NR05737K

We use an original water-based chemical method, to grow pure epitaxial BiFeO3 (BFO) ultra-thin films with excellent piezoelectric properties. Particularly, we show that this novel chemical route produces a higher natural ferroelectric domain size distribution and coercive field compared to similar BFO films grown by physical methods. Moreover, we measured the d33 piezoelectric coefficient of 60 nm thick BFO films with a direct approach, using Direct Piezoelectric Force Microscopy (DPFM). As a result, first piezo-generated charge maps of a very thin BFO layer were obtained applying this novel technology. We also performed a comparative study of the d33 coefficients between standard PFM analysis and the DPFM microscopy showing similar values i.e. 17 pm/V and 22 pC/N respectively. Finally, we proved that the directionality of the piezoelectric effect in BFO ferroelectric thin films is preserved at low thickness dimensions demonstrating the potential of chemical processes for the development of low cost functional ferroelectric and piezoelectric devices.

Defect landscape and electrical properties in solution-derived LaNiO3 and NdNiO3 epitaxial thin films

B. Mundet, J. Jareño, J. Gazquez, M. Varela, X. Obradors, and T. Puig. Phys. Rev. Materials 2, 063607 

DOI:https://doi.org/10.1103/PhysRevMaterials.2.063607

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.

Angular flux creep contributions in YBa2Cu3O7−δ nanocomposites from electrical transport measurements

F. Vallès, A. Palau, V. Rouco, B. Mundet, X. Obradors & T. Puig. Scientific Reports, volume 8, Article number: 5924(2018). 

doi:10.1038/s41598-018-24392-1

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.

Institut de Ciència de Materials de Barcelona ICMAB CSIC

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