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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

Ferroelectric HfO2 epitaxial films are of interest for determining intrinsic properties and for prototyping devices. Epitaxial (111)-oriented orthorhombic Hf0.5Zr0.5O2 films grown on La0.67Sr0.33MnO3/SrTiO3(001) are already being actively investigated. Now, we have explored the use of SrTiO3(111) substrates. We show that the orthorhombic phase is stabilized by tilted epitaxy, and the orientation of the orthorhombic crystallites is different from that of equivalent films on SrTiO3(001). The measured remanent polarization of above 14 µC cm-2 agrees well with the expected value considering the crystal orientation, the fraction of ferroelectric phase in the film, and the predicted polarization of ferroelectric HfO2. High endurance and retention are also measured. ; Financial support from the Spanish Ministry of Science and Innovation (MCIN/AEI/ 10.13039/501100011033), through the Severo Ochoa FUNFUTURE (CEX2019-000917-S), PID2020- 112548RB-I00 and PID2019-107727RB-I00 projects, from CSIC through the i-LINK (LINKA20338) program, and from Generalitat de Catalunya (2017 SGR 1377) is acknowledged. Project supported by a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. IF acknowledges Ramón y Cajal contract RYC-2017-22531. TS is financially supported by China Scholarship Council (CSC) with No. 201807000104. TS work has been done as a part of his Ph.D. program in Materials Science at Universitat Autònoma de Barcelona. SE acknowledges the Spanish Ministry of Science and Innovation for his PhD contract (SEV-2015-0496-16-3) and its cofunding by the ESF. ICTS-CNME at UCM is acknowledged for offering access to STEM microscopy and expertise. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

Electroresistance in ultrathin Hf0.5Zr0.5O2 (HZO) films is pivotal toward the implementation of hafnia-based ferroelectrics in electronics. Here, we show that the electroresistance yield and endurance of large capacitors (∼314 μm2) of epitaxial HZO films only 2.2 nm thick grown on SrTiO3 or GdScO3 can be improved using 1 nm SrTiO3 capping layers. It is argued that the main role of the capping layer is to minimize charge transport along grain boundaries, and, thus, a similar strategy can be explored in polycrystalline films. ; Financial support from the Spanish Ministry of Science and Innovation (MCIN/AEI/10.13039/501100011033) through the Severo Ochoa FUNFUTURE (Grant No. CEX2019-000917-S) and Grant Nos. PID2019-107727RB-I00, PID2020-112548RB-I00, and PID2020-118479RB-I00; the Consejo Superior de Investigaciones Científicas through i-LINK (Grant No. LINKA20338) program; and the Generalitat de Catalunya (Grant No. 2017 SGR 1377) are acknowledged. This project was supported by a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation. Xiao Long and Huan Tan are financially supported by the China Scholarship Council (CSC) under Grant Nos. 201806100207 and 201906050014. The work of Xiao Long and Huan Tan was done as a part of their Ph.D. program in Materials Science at Universitat Autònoma de Barcelona. Saúl Estandía acknowledges the Spanish Ministry of Economy, Competitiveness and Universities for his Ph.D. Contract (No. SEV-2015-0496-16-3) and its cofunding by the ESF. ; With funding from the Spanish government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000917-S). ; Peer reviewed

Scigaj, M. et al. ; The integration of epitaxial BaTiO3 films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO3/LaNiO3/SrTiO3 heterostructure is grown monolithically on Si(001). The BaTiO3 films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm2. This result paves the way towards the fabrication of lead-free BaTiO3 ferroelectric memories on silicon platforms. ; ICMAB-CSIC authors 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 MAT2014-56063-C2-1-R project, and from Generalitat de Catalunya (2014 SGR 734). Work at Oak Ridge National Laboratory was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. C. H. Chao acknowledges the NSC-CSIC 2014 Summer Program in Spain for Taiwanese PhD students. I. Fina acknowledges Juan de la Cierva – Incorporación postdoctoral fellowship (IJCI-2014-19102) from the Spanish Ministry of Economy and Competitiveness of Spanish Government. INL gratefully acknowledges the European commission and the national French research agency (ANR) for funding, through the projects SITOGA (FP7-ICT-2013-11-619456), TIPS (H2020‐ICT‐02-2014‐1-644453), ANR HIRIS and ANR DIAMWAFEL. INL also acknowledges P. Regreny, C. Botella and J.-B. Goure for MBE technical assistance. ; Peer reviewed

Half-metallic ferromagnetic La0.7Sr0.3MnO3 (LSMO) represents an appealing candidate to be integrated on silicon substrates for technological devices such as sensors, data storage media, IR detectors, and so on. Here, we report high-quality epitaxial LSMO thin films obtained by an original combination of chemical solution deposition (CSD) and molecular beam epitaxy (MBE). A detailed study of the thermal, chemical, and physical compatibility between SrTiO3 (STO)/Si buffer layers and LSMO films, grown by MBE and CSD, respectively, enables a perfect integration of both materials. Importantly, we show a precise control of the coercive field of LSMO films by tuning the mosaicity of the STO/Si buffer layer. These results demonstrate the enormous potential of combining physical and chemical processes for the development of low-cost functional oxide-based devices compatible with the complementary metal oxide semiconductor technology. ; ACG acknowledges the financial support from the French Agence Nationale pour la Recherche (ANR), project Q-NOSS ANR-16-CE09-0006-01 and École Centrale de Lyon under the BQR 2016 project. The research leading to these results has received funding from the European Union Seventh Framework Program under Grant Agreement 312483 - ESTEEM2 (Integrated Infrastructure Initiative–I3). This project has received funding from the EU‐H2020 research and innovation Program under grant agreement No 654360 having benefitted from the access provided by ICMAB-CSIC in Barcelona within the framework of the NFFA‐Europe Transnational Access Activity. Fruitful discussions with Pr. F. Rivadulla from USC are highly acknowledged. INL authors acknowledge the European Commission for funding the project TIPS (H2020-ICT-02-2014-1-644453). We thank P. Regreny, C. Botella, and J. B. Goure for the MBE technical assistance on the Nanolyon technological platform. ; 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

The Pr-based cobaltate Pr0.5Ca0.5CoO3 (PCCO) presents in bulk form a singular simultaneous valence and spin-state transition that turns the metallic state into insulator, and displays a large and ultrafast photoresponse in the insulating phase. Epitaxial thin films of PCCO have been grown by deposition on LaAlO3(001) (LAO) substrate, chosen to minimize the mismatch with the film. The films grow epitaxially with two times the substrate periodicity (2a0×2a0×2a0) and the long perovskite axis perpendicular to the surface. We report a reduction of the structural symmetry from Pnma (bulk) to P212121 (film). The P212121 symmetry revealed by synchrotron x ray remains at low temperatures. These PCCO films are metallic, and ferromagnetic below TC=170K, confirming the stabilization of excited Co3+ spin states and the suppression of the concurrent Co spin-state, valence, and metal-insulator transitions. Z-contrast imaging and electron-energy-loss spectroscopy elemental maps reveal long-range ordered oxygen vacancy planes unexpectedly stacking parallel to the interface, in spite of the tensile character of the PCCO/LAO heterostructure. In contrast to the general tendency reported for strained La0.5Sr0.5CoO3−δ (LSCO) films, we show that a nominal tensile strain can be also compatible with the presence of alternating O vacancy planes parallel to the interface, instead of perpendicular to it. That occurs thanks to the double cell of the film and the formation of the (1/2, 1/2, 1/2) superstructure studied in this work. These results expand the possibilities of controlling interfacial physical properties via engineering of ordered oxygen-defect structures in strongly correlated oxides. ; We acknowledge financial support from the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN), through Projects No. MAT2015-686760-02-2-P, No. RTI2018-098537-B-C21, and No. RTI2018-098537-BC22, and "Severo Ochoa" Programme for Centres of Excellence in R&D (Grant No. SEV-2015-0496). The former are cofunded by ERDF of European Union, as Project No. EFA194/16 TNSI (POCTEFA/UE-FEDER). We thank also the Spanish MICINN and the Consejo Superior de Investigaciones Científicas for financial support and for provision of synchrotron radiation facilities (Grant No. CRG-BM25B, ESRF). J.G. acknowledges the Ramon y Cajal program (Grant No. RYC-2012-11709). Research at ORNL (STEM-EELS) was supported by the US Department of Energy (DOE), Basic Energy Sciences (BES), Materials Sciences and Engineering Division (SJP and MV). ; Peer reviewed

Multifunctional magnetic nanocomposites based on mesoporous silica have a wide range of potential applications in catalysis, biomedicine, or sensing. Such particles combine responsiveness to external magnetic fields with other functionalities endowed by the agents loaded inside the pores or conjugated to the particle surface. Different applications might benefit from specific particle morphologies. In the case of biomedical applications, mesoporous silica nanospheres have been extensively studied while nanorods, with a more challenging preparation, have attracted much less attention despite the positive impact on the therapeutic performance shown by seminal studies. Here, we report on a sol-gel synthesis of mesoporous rodlike silica particles of two distinct lengths (1.4 and 0.9 μm) and aspect ratios (4.7 and 2.2) using Pluronic P123 as a structure-directing template and rendering ∼1 g of rods per batch. Iron oxide nanoparticles have been synthesized within the pores yielding maghemite (γ-Fe2O3) nanocrystals of elongated shape (∼7 nm × 5 nm) with a [110] preferential orientation along the rod axis and a superparamagnetic character. The performance of the rods as T2-weighted MRI contrast agents has also been confirmed. In a subsequent step, the mesoporous silica rods were loaded with a cerium compound and their surface was functionalized with fluorophores (fluorescamine and Cyanine5) emitting at λ = 525 and 730 nm, respectively, thus highlighting the possibility of multiple imaging modalities. The biocompatibility of the rods was evaluated in vitro in a zebrafish (Danio rerio) liver cell line (ZFL), with results showing that neither long nor short rods with magnetic particles caused cytotoxicity in ZFL cells for concentrations up to 50 μg/ml. We advocate that such nanocomposites can find applications in medical imaging and therapy, where the influence of shape on performance can be also assessed. ; The authors acknowledge financial support from the Spanish Ministry of Science and Innovation through the RTI2018-096273-B-I00 project, the 'Severo Ochoa' Programme for Centers of Excellence in R&D (CEX2019-000917-S). The Generalitat de Catalunya, project 2017SGR765, is also acknowledged. This research work was performed in the framework of the Nanomedicine CSIC HUB (ref 202180E048).The authors participate in the Aerogels COST ACTION (CA 18125). J.G. received financial support through the "la Caixa" INPhINIT Fellowship Grant for Doctoral Studies at Spanish Research Centers of Excellence (Grant code: LCF/BQ/DI17/11620041), "la Caixa" Banking Foundation (ID100010434), Barcelona, Spain. J.G. was enrolled in the doctoral program in Materials Science at the UAB. M.T. (ref RYC2019-026841-I) has a post-doctoral fellowship "Ramón y Cajal" supported by the "Ministerio de Ciencia e Innovación", Spanish Government. A. G. has been supported by the fellowship from Instituto de Salud Carlos III with FEDER funds (FI17/00073). A.Rosell and A. G. work takes part within the RETICS-INVICTUS PLUS from Instituto de Salud Carlos III with FEDER funds (RD16/0019/0021). G. Antorrena from the LMA at Universidad de Zaragoza is acknowledged for performing XPS measurements. ICTS-CNME at UCM is also acknowledged for offering access to STEM and expertise. The ICMAB Scientific services of electron microscopy, low temperatures and magnetometry, thermal analysis, and X-ray diffraction have performed measurements for the present work. Nico Dix, Joan Esquius, and Xavi Campos are acknowledged by making possible SAXS measurements at the ICMAB X-ray diffraction service. ; Peer reviewed