Suchergebnisse

Enhanced pinning due to nanoscale strain is unique to the high-Tc cuprates, where pairing may be modified with lattice distortion. Therefore a comprehensive understanding of the defect landscape is required for a broad range of applications. However, determining the type and distribution of defects and their associated strain constitutes a critical task, and for this aim, real-space techniques for atomic resolution characterization are necessary. Here, we use scanning transmission electron microscopy (STEM) to study the atomic structure of individual defects of solution-derived YBa2Cu3O7 (YBCO) nanocomposites, where the inclusion of incoherent secondary phase nanoparticles within the YBCO matrix dramatically increases the density of Y1Ba2Cu4O8 (Y124) intergrowths, the commonest defect in YBCO thin films. The formation of the Y124 is found to trigger a concatenation of strain-derived interactions with other defects and the concomitant nucleation of intrinsic defects, which weave a web of randomly distributed nanostrained regions that profoundly transform the vortex-pinning landscape of the YBCO nanocomposite thin films. ; Authors acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0496), CONSOLIDER Excellence Network (MAT2015-68994-REDC), COACHSUPENERGY project (MAT2014-51778-C2-1-R, co-financed by the European Regional Development Fund), European Research Council Advanced Grant Award ERC-2014-ADG-669504, and from the Catalan Government with 2014-SGR-753 and Xarmae. J.G. and M.C. acknowledge Ramon y Cajal Program (RyC-2012- 11709 and RYC-2013-12448, respectively). The microscopy work were conducted in the Laboratorio de Microscopias Avanzadas at Instituto de Nanociencia de Aragon - Universidad de Zaragoza (Zaragoza, Spain). Authors acknowledge the LMA-INA for offering access to their instruments and expertise. ; Peer reviewed

In this work we evaluate the defects and the associated distortions present in tensile and compressive-strained chemical solution deposition (CSD) derived NdNiO3 (NNO) and LaNiO3 (LNO) thin-films by means of aberration corrected Scanning Transmission Electron Microscopy (STEM). 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 RPFs 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 (MIT) to shift to higher temperatures. ; We acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0496), CONSOLIDER Excellence Network (MAT2015-68994-REDC), COACHSUPENERGY project (MAT2014-51778-C2-1-R and BES-2015-072749 grant for B.M, co-financed by the European Regional Development Fund) and from the Catalan Government with 2017 SGR 1519 and Xarmae. J.J. acknowledges an FPU grant (FPU14/05960) from Ministerio español de Educación, Cultura y Deporte para la Formación de Profesorado Universitario and J.G. acknowledges the Ramon y Cajal program (RyC-2012–11709). The STEM microscopy work was conducted in the ICTS-CNME at UCM as well as at the Laboratorio de Microscopias Avanzadas (LMA) at Instituto de Nanociencia de Aragon (INA) at the University of Zaragoza. Authors acknowledge the ICTS-CNME for offering access to their instruments and expertise. Electron microscopy performed at the Centro Nacional de Microscopía Electrónica (UCM) were sponsored by the ERC Starting Investigator Award No. STEMOX#239739. ; Peer reviewed

It is well known that in the high-temperature superconductor YBa2Cu3O7−x (YBCO), oxygen vacancies (VO) control the carrier concentration, its critical current density and transition temperature. In this work, it is revealed that VO also allows the accommodation of local strain fields caused by large-scale defects within the crystal. We show that the nanoscale strain associated with Y2Ba4Cu8O16 (Y124) intergrowths— that are common defects in YBCO—strongly affect the venue and concentration of VO. Local probe measurements in conjunction with density-functional-theory calculations indicate a strain-driven reordering of VO from the commonly observed CuO chains towards the bridging apical sites located in the BaO plane and bind directly to the superconducting CuO2 planes. Our findings have strong implications on the physical properties of the YBCO, as the presence of apical VO alters the transfer of carriers to the CuO2 planes, confirmed by changes in the Cu and O core-loss edge probed using electron energy loss spectroscopy, and creates structural changes that affect the Cu–O bonds in the superconducting planes. In addition, the revelation of apical VO also has implications on modulating critical current densities and enhancing vortex pinning. ; We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through the 'Severo Ochoa' Programme for Centres of Excellence in R&D (SEV-2015-0496), and the COACHSUPENERGY project (SUMATE – RTI2018-095853-B-C21, co-financed by the European Regional Development Fund). B. M, R. G., J. G., T. P. and X. O also thank the European Union for its support under the EUROTAPES project (FP7-NMP-Large-2011-280432), ULTRASUPERTAPE project (ERC-2014-ADG-669504), and COST Action NANOCOHYBRI (CA16218), and from the Catalan Government under 2017-SGR-1519 and Xarmae. J. G. also acknowledges the Ramon y Cajal Program (RYC-2012-11709). S. H. and R. M. acknowledge financial support from the National Science Foundation (NSF) grant DMR-1806147. STEM imaging and analysis at 200 kV was sponsored by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, and STEM imaging at 100 kV was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Computations in this work benefited from the use of the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by NSF grants ACI-1053575 and ACI-1548562. ; Peer reviewed

An attempt to grow a thin epitaxial composite film of YBa2Cu3O7-δ (YBCO) with spinel MnFe2O4 (MFO) nanoparticles on a LAO substrate using the CSD approach resulted in a decomposition of the spinel and various doping modes of YBCO with the Fe and Mn cations. These nanostructural effects lead to a lowering of Tc and a slight Jc increase in field. Using a combination of advanced transmission electron microscopy (TEM) techniques such as atomic resolution high-angle annular dark field scanning transmission electron microscopy, energy dispersive X-ray spectroscopy and electron energy-loss spectroscopy we have been able to decipher and characterize the effects of the Fe and Mn doping on the film architecture. The YBaCuFeO5 anion-deficient double perovskite phase was detected in the form of 3D inclusions as well as epitaxially grown lamellas within the YBCO matrix. These nano-inclusions play a positive role as pinning centers responsible for the Jc/Jsf (H) dependency smoothening at high magnetic fields in the YBCO-MFO films with respect to the pristine YBCO films. ; The authors gratefully acknowledge Prof. Dr. A. Abakumov and Dr. J. Gazquez for discussions and corrections. Part of this work was performed within the framework of the EUROTAPES project (FP7-NMP.2011.2.2-1 Grant no. 280432), funded by the European Union. ICMAB research was financed by the Ministry of Economy and Competitiveness, and FEDER funds under the projects MAT2011-28874-C02-01, MAT2014-51778-C2-1-R, ENE2014-56109-C3-3-R and Consolider Nanoselect CSD2007-00041, and by Generalitat de Catalunya (2009 SGR 770, 2015 SGR 753 and Xarmae). ICMAB acknowledges support from Severo Ochoa Program (MINECO, Grant SEV-2015-0496). ; Peer reviewed