Epitaxial YBa2Cu3O7-x nanocomposite thin films from colloidal solutions

A methodology of general validity to prepare epitaxial nanocomposite films based on the use of colloidal solutions containing different crystalline preformed oxide nanoparticles (ex situ nanocomposites) is reported. The trifluoroacetate (TFA) metal-organic chemical solution deposition route is used with alcoholic solvents to grow epitaxial YBaCuO (YBCO) films. For this reason stabilizing oxide nanoparticles in polar solvents is a challenging goal. We have used scalable nanoparticle synthetic methodologies such as thermal and microwave-assisted solvothermal techniques to prepare CeO and ZrO nanoparticles. We show that stable and homogeneous colloidal solutions with these nanoparticles can be reached using benzyl alcohol, triethyleneglycol, nonanoic acid, trifluoroacetic acid or decanoic acid as protecting ligands, thereby allowing subsequent mixing with alcoholic TFA solutions. An elaborate YBCO film growth analysis of these nanocomposites allows the identification of the different relevant growth phenomena, e.g. nanoparticles pushing towards the film surface, nanoparticle reactivity, coarsening and nanoparticle accumulation at the substrate interface. Upon mitigation of these effects, YBCO nanocomposite films with high self-field critical currents (J ∼ 3-4 MA cm at 77 K) were reached, indicating no current limitation effects associated with epitaxy perturbation, while smoothed magnetic field dependences of the critical currents at high magnetic fields and decreased effective anisotropic pinning behavior confirm the effectiveness of the novel developed approach to enhance vortex pinning. In conclusion, a novel low cost solution-derived route to high current nanocomposite superconducting films and coated conductors has been developed with very promising features.All authors acknowledge the EU (EU-FP7 NMP-LA-2012-280432 EUROTAPES project). ICMAB acknowledges MINECO (MAT2014-51778-C2-1-R) and Generalitat de Catalunya (2014SGR 753 and Xarmae). UGhent acknowledges the Special Research Fund (BOF), the Research Foundation Flanders (FWO) and the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT). TEM microscopy work was conducted in the Catalan Institute of Nanoscience and Nanotechnology (ICN2). The authors acknowledge the ICN2 Electron Microscopy Division for offering access to their instruments and expertise. Part of the STEM microscopy work was conducted in 'Laboratorio de Microscopias Avanzadas' at the Instituto de Nanociencia de Aragon—Universidad de Zaragoza. The authors acknowledge the LMA-INA for offering access to their instruments and expertise. JG and MC also acknowledge the Ramon y Cajal program (RYC-2012-11709 and RYC-2013-12448 respectively).Peer Reviewe

Mapping Orthorhombic Domains with Geometrical Phase Analysis in Rare-Earth Nickelate Heterostructures

Most perovskite oxides belong to the Pbnm space group, composed by an anisotropic unit cell, A-site antipolar displacements and oxygen octahedral tilts. Mapping the orientation of the orthorhombic unit cell in epitaxial heterostructures that consist of at least one Pbnm compound is often required to understand and control the different degrees of coupling established at their coherent interfaces and, therefore, their resulting physical properties. However, retrieving this information from the strain maps generated with high-resolution scanning transmission electron microscopy can be challenging, because the three pseudocubic lattice parameters are very similar in these systems. Here, we present a novel methodology for mapping the crystallographic orientation in Pbnm systems. It makes use of the geometrical phase analysis algorithm, as applied to aberration-corrected scanning transition electron microscopy images, but in an unconventional way. The method is fast and robust, giving real-space maps of the lattice orientations in Pbnm systems, from both cross-sectional and plan-view geometries and across large fields of view. As an example, we apply our methodology to rare-earth nickelate heterostructures, in order to investigate how the crystallographic orientation of these films depends on various structural constraints that are imposed by the underlying single crystal substrates. We observe that the resulting domain distributions and associated defect landscapes mainly depend on a competition between the epitaxial compressive/tensile and shear strains, together with the matching of atomic displacements at the substrate/film interface. The results point towards strategies for controlling these characteristics by appropriate substrate choice.Comment: 32 pages, 5 figures, 2 table

Probing localized strain in solution-derived YBa2Cu3O7−δ nanocomposite thin films

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 reviewe

Competition between Carrier Injection and Structural Distortions in Electron‐Doped Perovskite Nickelate Thin Films

The discovery of superconductivity in doped infinite‐layer nickelate thin films has brought increased attention to the behavior of the doped perovskite phase. Despite this interest, the majority of existing studies pertain to hole‐doped perovskite rare‐earth nickelate thin films, while most electron‐doping studies have been performed on bulk materials so far. To tackle this imbalance, a detailed study that addresses doping of NdNiO$_{3}$ thin films using A‐site substitution is presented, using Pb as a dopant and taking advantage of its valence‐skipping nature. Through a combination of complementary techniques including X‐ray diffraction, transport measurements, X‐ray absorption spectroscopy, electron energy‐loss spectroscopy and scanning transmission electron microscopy, the valence of Pb in the Nd$_{1−x}$Pb$_{x}$NiO$_{3}$ structure is confirmed to be 4+, and the behavior of the doped thin films is found to be controlled by a competition between carrier injection and structural distortions, which respectively reduce and increase the metal‐to‐insulator transition temperature. This work provides a systematic study of electron doping in NdNiO$_{3}$, demonstrating that A‐site substitution with Pb is an appropriate method for such doping in perovskite rare‐earth nickelate systems

Competition between Carrier Injection and Structural Distortions in Electron-Doped Perovskite Nickelate Thin Films

The discovery of superconductivity in doped infinite-layer nickelate thin films has brought increased attention to the behavior of the doped perovskite phase. Despite this interest, the majority of existing studies pertain to hole-doped perovskite rare-earth nickelate thin films, while most electron-doping studies have been performed on bulk materials so far. To tackle this imbalance, a detailed study that addresses doping of NdNiO thin films using A-site substitution is presented, using Pb as a dopant and taking advantage of its valence-skipping nature. Through a combination of complementary techniques including X-ray diffraction, transport measurements, X-ray absorption spectroscopy, electron energy-loss spectroscopy and scanning transmission electron microscopy, the valence of Pb in the NdPbNiO structure is confirmed to be 4+, and the behavior of the doped thin films is found to be controlled by a competition between carrier injection and structural distortions, which respectively reduce and increase the metal-to-insulator transition temperature. This work provides a systematic study of electron doping in NdNiO, demonstrating that A-site substitution with Pb is an appropriate method for such doping in perovskite rare-earth nickelate systems

High Performance of Superconducting YBa2Cu3O7 Thick Films Prepared by Single-Deposition Inkjet Printing

Inkjet printing (IJP) is a very appealing cost-effective deposition technique to achieve large-area solution-derived functional films. For many applications, it is very challenging to increase the film thickness in order to achieve competitive performance, for instance, high critical currents in superconducting films. In this paper, the preparation of superconducting YBa2Cu3O7 thick films (∼1.1 μm) using a single deposition is reported. Specific rules for ink design, deposition protocols, and pyrolysis processes are provided. The most important aspect is to formulate an ink with a solvent having a high boiling point that keeps the whole film wet during deposition to avoid liquid movement due to coffee-ring effects. An additional success has been to modify the ink with a photocurable polyacrylic ester varnish which after polymerization with a UV LED lamp helps keep homogeneous thickness. This varnish also helped avoid the generation of film instabilities (wrinkling or cracking) during pyrolysis. Homogeneous pyrolyzed thick films are transformed into epitaxial thick films with high critical currents. The IJP process is shown to be valid to prepare nanocomposite films using colloidal inks including pre-prepared BaZrO3 nanoparticles. The nanocomposite thick films display enhanced vortex pinning, thus keeping high critical currents under high magnetic fields.The authors acknowledge the EUROTAPES project (EU-FP7 NMP-LA-2012-280432), COACHSUPENERGY (MAT2014- 51778-C2-1-R and MAT2014-51778-C2-2-R), SUMATE (RTI2018-095853-BC21 and RTI2018-095853-B-C22) cofinanced by the European Regional Development Fund and SUPERINKS (RTC-2015-3840-S) from MINECO (cofinanced by the European Regional Development Fund), 2017-SGR 753 from Generalitat de Catalunya, and COST Action NANOCOHYBRI (CA16218). ICMAB authors acknowledge the Center of Excellence awards Severo Ochoa SEV2015-0496 and CEX2019-000917-S. The authors acknowledge the Scientific Services at ICMAB, ICN2 Electron Microscopy Division, and LMA-INA from Aragon. They also acknowledge KAO Chimigraf for providing varnishes and Bruker HTS for providing metallic substrates.Peer reviewe

Atomic-scale characterization of structural distortions in perovskite oxide thin films

El desenvolupament de nous dispositius, cada cop més complexes, que s’adeqüin a les necessitats del mercat s’està convertint en una tasca cada cop més complicada deguda a la gairebé completa explotació de les propietats ofertes pels materials actuals. No obstant, és possible desenvolupar dispositius que ofereixin noves funcionalitats a través de la fabricació d’heteroestructures epitaxials (a l’escala nano-mètrica) compostes per diferents materials, on les propietats de cadascun dels compostos emprats són alterades degut a la seva interacció mútua. Quan aquestes estructures estan formades per òxids del tipus “perovskita”, existeix una forta interacció entre els diferents graus de llibertat dels electrons (xarxa cristal·lina, espín, òrbita i càrrega) donant lloc a un gran ventall de propietats físiques fascinants, que, a més, poden ser modificades a mida mitjançant la subtil alteració de les seves propietats estructurals a través de la tensions. Per tal d’entendre els fenòmens físics que donen lloc a aquest tipus d’efectes, és necessari conèixer l’estructura real dels defectes i/o distorsions que apareixen en aquestes estructures. Per aquesta raó, és indispensable l’ús de noves tècniques de caracterització capaces d’analitzar en l’espai real i amb resolució atòmica aquests sistemes. El desenvolupament de la tècnica de la microscòpia electrònica de transmissió d’escaneig corregida d’aberracions, combinada amb la espectroscòpia EELS (STEM-EELS), va significar un avanç notable ja que aquesta tècnica permet la observació directe d’estructures complexes i no periòdiques (així com defectes o interfases) en l’espai real i amb resolució subatòmica, sense la necessitat d’emprar simulacions numèriques. En aquest treball, s’aborden tres casos paradigmàtics de distorsions estructurals derivades de les tensions en capes fines epitaxials d’òxids tipus perovskita. En primer lloc, s’ investiga la forta interacció entre la microestructura, els tipus de defectes i les propietats superconductores de les capes fines de YBa2Cu3O7 del tipus nanocompost, on nanopartícules orientades aleatòriament resten atrapades dins de la pròpia matriu del YBCO. A més, s’ estudia en detall totes les distorsions que apareixen al voltant d’un dels defectes més comuns observats en aquest tipus de capes, que també tenen una influencia rellevant en les seves propietats superconductores. En segon lloc, s’ estudien els mecanismes estructurals que ajuden en l’acomodació de la tensió epitaxial, tan compressiva con expansiva, en les capes fines de LaNiO3 (LNO) i NdNiO3 (NNO), crescudes sobre monocristalls de LAO i LSAT, respectivament. S’observa la formació de dos tipus diferents de defectes en funció del compostos emprats, tant en la capa com en el substrat. Les propietats de transport elèctric de les capes són també investigades per tal de correlacionar els defectes generats i les propietats macroscòpiques de les capes. Finalment s’ investiguen els efectes de disminuir el gruix de les capes de La0.7Sr0.3MnO3 fins a l’ordre d’uns pocs nanòmetres. S’observa l’aparició d’una transició des d’un estat ferromagnètic i metàl·lic cap a un altre ferromagnètic i aïllant quan el gruix de les capes és reduït per sota d’un gruix crític, fet que contradiu el mecanisme de transport elèctric esperat en aquest compost: el conegut com a intercanvi doble o “double-exchange mechanism”. S’aporta una nova visió d’aquest fenomen a través de la caracterització de les modificacions estructurals que tenen lloc en aquestes capes, que apareixen degut a la tensió epitaxial i al confinament espacial. Es creu que les propietats estructurals mostrades poden ajudar en l’entesa de les alteracions de les propietats físiques observades en les capes de LSMO quan aquestes són reduïdes a uns pocs nanòmetres.The continuous development of novel and complex devices for fulfilling the market demands is becoming more complex over time because of the wholly exploitation of the available bulk materials. One possibility to accomplish novel devices possessing new functionalities is by engineering epitaxial heterostrucutres, in the nanometric scale, where the properties of the used compounds can be modified because of their mutual interaction. When these heterostructures are made of perovskite oxides, the strong interplay between the lattice, spin, orbit and charge degrees of freedom lead to a huge range of fascinating properties that can be tailored by the subtle structural modifications induced by strains. In order to understand the underlying physics behind these phenomena, it is crucial to know the real structure of the emerging lattice defects or distortions within these kind of structures. For this reason, new techniques capable of analyzing these systems in the real space with atomic resolution are required. The development of the aberration-corrected scanning transmission electron microscopy, combined with the electron energy loss spectroscopy, technique (STEM-EELS) marked a notable breakthrough as it permits to directly see, without the need of simulations, the real structure of complex non-periodical structures, such as defects or interfaces, in real space and with sub-atomic resolution. In this work, we address three paradigmatic examples of strain-driven structural distortions appearing in one of the most studied family of functional oxides materials, this is, the case of perovskite oxides. First, we investigate the strong interplay between the microstructure, the defect landscape and the superconducting properties of YBa2Cu3O7 nanocomposite films, where randomly oriented nanoparticles are trapped within the YBCO host matrix. Besides, we analyze in detail all the emerging distortions around one of the most common defect found in YBCO nanocomposite films, which will also ultimately impinge on its superconducting properties. Second, we study in detail the structural mechanisms that help on the accommodation of the epitaxial strain, either compressive or tensile, in LaNiO3 (LNO) and NdNiO3 (NNO) thin films grown onto LAO and LSAT single crystal substrates, respectively. Two different kind of defects are identified in the studied heterostructures, which are observed to appear depending on the used compound and substrate. The electrical transport properties are also under investigation in order to find out the implications of the generated defect landscapes in the macroscopic properties of the films. Finally, we investigate the effect of reducing the film thickness of La0.7Sr0.3MnO3 thin films down to few nanometers. A transition from a ferromagnetic-metallic to a ferromagnetic-insulating phase is identified when films are reduced below a critical thickness, which contradicts the electrical transport mechanism expected for this compound. We provide new insights on the structural modifications generated by the epitaxial strain and the spatial confinement effects in these ultrathin films, which might help to understand the observed modifications on the LSMO physical properties

Study of the development of a permanent magnet synchronous machines, (PMSM), pre-design tool

This study contains all the aspects to understand what is a permanent magnet synchronous machine and how does it works. The study is based on the development of a pre-design tool for a PMSM on the Matlab® environment, and it also includes the mathematical model validation as well as the development of a graphic user interface, where the user is able to introduce the inputs of the required PMSM and the output data will be shown

Study of the development of a permanent magnet synchronous machines, (PMSM), pre-design tool

This study contains all the aspects to understand what is a permanent magnet synchronous machine and how does it works. The study is based on the development of a pre-design tool for a PMSM on the Matlab® environment, and it also includes the mathematical model validation as well as the development of a graphic user interface, where the user is able to introduce the inputs of the required PMSM and the output data will be shown