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SrSnO3 (SSO) is an emerging ultrawide band gap (UWBG) semiconductor with potential in high-power applications. In-plane compressive strain was recently shown to stabilize the high-temperature tetra...

We demonstrate the impact of subtle changes in molecular structure on the singlet and triplet exciton diffusion lengths (LD) for derivatives of the archetypical electron-transport material 4,7-diphenyl-1,10-phenanthroline (BPhen). Specifically, this work offers a systematic characterization of singlet and triplet exciton transport in identically prepared thin films, highlighting the differing dependence on molecular photophysics and intermolecular spacing. For luminescent singlet excitons, photoluminescence quenching measurements yield an LD from

Cobalt oxides have long been understood to display intriguing phenomena known as spin-state crossovers, where the cobalt ion spin changes vs. temperature, pressure, etc. A very different situation was recently uncovered in praseodymium-containing cobalt oxides, where a first-order coupled spin-state/structural/metal-insulator transition occurs, driven by a remarkable praseodymium valence transition. Such valence transitions, particularly when triggering spin-state and metal-insulator transitions, offer highly appealing functionality, but have thus far been confined to cryogenic temperatures in bulk materials (e.g., 90 K in Pr1-xCaxCoO3). Here, we show that in thin films of the complex perovskite (Pr1-yYy)1-xCaxCoO3-{\delta}, heteroepitaxial strain tuning enables stabilization of valence-driven spin-state/structural/metal-insulator transitions to at least 291 K, i.e., around room temperature. The technological implications of this result are accompanied by fundamental prospects, as complete strain control of the electronic ground state is demonstrated, from ferromagnetic metal under tension to nonmagnetic insulator under compression, thereby exposing a potential novel quantum critical point., Comment: 35 pages, 7 figures

We investigated temperature dependent current driven spin-orbit torques in magnetron sputtered ${\mathrm{Ru}}_{2}{\mathrm{Sn}}_{3}$ (4 and 10 nm)/${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ (5 nm) layered structures with in-plane magnetic anisotropy. The room temperature dampinglike and fieldlike spin torque efficiencies of the amorphous ${\mathrm{Ru}}_{2}{\mathrm{Sn}}_{3}$ films were measured to be $0.14\ifmmode\pm\else\textpm\fi{}0.008\phantom{\rule{0.16em}{0ex}}(0.07\ifmmode\pm\else\textpm\fi{}0.012)$ and $--0.03\ifmmode\pm\else\textpm\fi{}0.006\phantom{\rule{0.16em}{0ex}}(--0.20\ifmmode\pm\else\textpm\fi{}0.009)$, for the four (10 nm) films, respectively, by utilizing the second-harmonic Hall technique. The large fieldlike torque in the relatively thicker ${\mathrm{Ru}}_{2}{\mathrm{Sn}}_{3}$ (10 nm) thin film is unique compared to the traditional spin Hall materials interfaced with thick magnetic layers with in-plane magnetic anisotropy which typically have dominant dampinglike and negligible fieldlike torques. Additionally, the observed room temperature fieldlike torque efficiency in ${\mathrm{Ru}}_{2}{\mathrm{Sn}}_{3}$ (10 nm)/CoFeB (5 nm) is up to three times larger than the dampinglike torque ($--0.20\ifmmode\pm\else\textpm\fi{}0.009$ and $0.07\ifmmode\pm\else\textpm\fi{}0.012$, respectively) and 30 times larger at 50 K ($--0.29\ifmmode\pm\else\textpm\fi{}0.014$ and $0.009\ifmmode\pm\else\textpm\fi{}0.017$, respectively). The temperature dependence of the fieldlike torques shows dominant contributions from the intrinsic spin Hall effect while the dampinglike torques show dominate contributions from the extrinsic spin Hall effects, skew scattering, and side jump. Through macrospin calculations, we found that including fieldlike torques on the order of or larger than the dampinglike torque can reduce the switching critical current and decrease magnetization procession for a perpendicular ferromagnetic layer.

InOx films that are less disordered than those exhibiting direct quantum superconductor-insulator transitions feature quantum superconductor-metal transitions tuned by magnetic field. Resistance data across this superconductor-metal transition obey activated scaling, with critical exponents suggesting that the transition is governed by an infinite-randomness critical point in the universality class of the random transverse-field Ising model in two dimensions. The transition is accompanied by quantum Griffiths effects. This unusual behavior is expected for systems with quenched disorder in the presence of ohmic dissipation. Disorder leads to the formation of large rare regions which are locally ordered superconducting puddles dispersed in a metallic matrix. Their dissipative dynamics causes the activated scaling, as predicted by a renormalization group theory.

The Josephson effect results from the coupling of two superconductors across a spacer such as an insulator, a normal metal or a ferromagnet to yield a phase coherent quantum state. However, in junctions with ferromagnetic spacers, very long-range Josephson effects have remained elusive. Here we demonstrate extremely long-range (micrometric) high-temperature (tens of kelvins) Josephson coupling across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7. These planar junctions, in addition to large critical currents, display the hallmarks of Josephson physics, such as critical current oscillations driven by magnetic flux quantization and quantum phase locking effects under microwave excitation (Shapiro steps). The latter display an anomalous doubling of the Josephson frequency predicted by several theories. In addition to its fundamental interest, the marriage between high-temperature, dissipationless quantum coherent transport and full spin polarization brings opportunities for the practical realization of superconducting spintronics, and opens new perspectives for quantum computing. Josephson coupling over micrometres and at tens of kelvins is demonstrated across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7.

Understanding the impact of strain on organic semiconductors is important for the development of electronic devices and sensors that are subject to environmental changes and mechanical stimuli; it is also important for understanding the fundamental mechanisms of charge trapping. Following our previous study on the strain effects in rubrene, we present here only the second example of the strain-work function relationship in an organic semiconductor; in this case, the benchmark material tetracene. Thin, platelike single crystals of tetracene with large (001) facets were laminated onto silicon and rubber substrates having significantly different coefficients of thermal expansion; mechanical strain in tetracene was subsequently induced by varying the temperature of the assembly. Tensile and compressive strains parallel to the (001) major facet were measured by grazing incidence X-ray diffraction, and the corresponding shifts in the electronic work functions were recorded via scanning Kelvin probe microscopy (SKPM). The work function of the tetracene (001) crystal surface directly correlated with the net mechanical strain and increased by ∼100 meV for in-plane tensile strains of 0.1% and decreased by approximately the same amount for in-plane compressive strains of -0.1%. This work provides evidence of the general and important impact of strain on the electrical properties of van der Waals bonded crystalline organic semiconductors and thereby supports the hypothesis that heterogeneous strains, for example in thin films, can be a major source of static electronic disorder.

Semiconductor materials with independently controlled electrical and thermal properties have a unique promise for energy-related applications from thermoelectrics and thermophotovoltaics. Here, using nonthermal plasma synthesized, direct-contact zinc oxide (ZnO) nanocrystal (NC) networks infilled with amorphous $\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$, and amorphous ZnO-$\mathrm{A}{\mathrm{l}}_{2}{\mathrm{O}}_{3}$ mixture, it is shown that such independent control of electrical and thermal properties is achievable. In this study, in addition to our early reports on control of the electrical properties in these two-phase nanocomposites by tailoring the contact radius between NCs, we demonstrate that the infill composition has a significant impact on the overall thermal conductivity of the NC network and can be used for thermal control. It is also shown that in these heterogeneous systems, the phonons are the dominant heat carriers, and the NC-NC contact radius has a negligible effect on thermal transport. The work suggests that this paradigm of independently controlling the electrical and thermal properties of NC-based materials through tuning the NC-NC contact radius and infill composition can be exploited even further by varying NC and infill materials with potential applications ranging from solar cells and light emitting diodes to solid-state energy converters.

Development of novel magnetic materials is of interest for fundamental studies and applications such as spintronics, permanent magnetics, and sensors. We report on the first experimental realization of single element ferromagnetism, since Fe, Co, and Ni, in metastable tetragonal Ru, which has been predicted. Body-centered tetragonal Ru phase is realized by use of strain via seed layer engineering. X-ray diffraction and electron microscopy confirm the epitaxial mechanism to obtain tetragonal phase Ru. We observed a saturation magnetization of 148 and 160 emu cm−3 at room temperature and 10 K, respectively. Control samples ensure the ferromagnetism we report on is from tetragonal Ru and not from magnetic contamination. The effect of thickness on the magnetic properties is also studied, and it is observed that increasing thickness results in strain relaxation, and thus diluting the magnetization. Anomalous Hall measurements are used to confirm its ferromagnetic behavior., Until now, there have been three choices for a room temperature (RT) single element ferromagnetic material in fundamental studies and applications. Here the authors achieved body-centered tetragonal phase ruthenium thin films by epitaxial growth, which is the 4th RT ferromagnetic single element material.

We report a synthesis procedure for dodecanethiol capped wurtzite ZnO nanocrystals with an average diameter of 4 nm that are monodisperse, highly soluble, and shelf-stable for many months. Compared to previous ZnO ink recipes, we demonstrate improved particle solubility and excellent ink stability, resulting in ZnO nanocrystal inks that are optimized for printed electronics applications. The ZnO nanocrystal solution exhibits an absorption peak at 341 nm (3.63 eV), which represents a blue-shift of approximately 0.3 eV from the bulk ZnO bandgap (∼3.3 eV). This blue shift is consistent with previously reported models for an increased bandgap due to quantum confinement. We used variable-angle spectroscopic ellipsometry (VASE) to determine the optical properties of solution-processed thin films of ZnO nanocrystals, which provides valuable insight into the changes in film composition and morphology that occur during thermal annealing treatments ranging from 150–300 °C. The ZnO nanocrystals maintain their quantum confinement when deposited into a thin film, and the degree of quantum confinement is gradually reduced as the thermal annealing temperature increases. Using infrared absorption measurements (FTIR) and X-ray photoelectron spectroscopy (XPS), we show that the dodecanethiol ligands are removed from the ZnO films during annealing, resulting in a high-purity semiconductor film with very low carbon contamination. Furthermore, we show that annealing at 300 °C results in complete ligand removal with only a slight increase in grain size. Thin-film transistors (TFT) using ZnO nanocrystals as the channel material annealed at 300 °C show moderate mobility (∼0.002 cm2 V−1 s−1) and good on/off ratio >104. These results demonstrate the distinct advantages of colloidal nanocrystals for printed electronics applications: the composition and morphology of the solution-processed film can be carefully tuned by controlling the size and surface coating of the nanocrystals in the ink.

We recently demonstrated that the superconductor-to-insulator transition induced by ionic liquid gating of the high temperature superconductor YBa

The manufacture of oral dosage form may induce changes in the physical form of an active pharmaceutical ingredient. One such example includes formation of hydrate during granulation followed by the reverse transition to the anhydrous form during drying. We used naproxen sodium dihydrate (DH) as the model compound and studied its dehydration at elevated temperature under different processing conditions, (i) in ambient air, (ii) in flow of inert gas (iii) under low pressure environment, and (iv) under 'high' pressure in closed environments. In situ variable temperature X-ray diffraction was used to monitor kinetics of phase transformation under these processing conditions. The DH dehydration was fastest under the flow of inert gas and slowest in closed environment. Polyvinyl pyrrolidone (PVP) and microcrystalline cellulose (MCC), commonly used hygroscopic solids, were used as the model excipients to monitor influence of excipients in modulating DH dehydration behavior under different processing conditions. Both the excipients altered the kinetics as well as the extent of DH dehydration, with PVP delaying and MCC facilitating the transformation under all processing conditions studied. The results indicate that the physical form of API, such as hydrate or anhydrous in the present case, in the formulation may be modulated by rational excipient selection.

This work reports on magnetocapacitance (MC) effects in epitaxial heterostructures of nominally 15 unit cells (u.c.) LaMnO3 (LMO) and 2 u.c. SrTiO3 (STO) with an alternating layer-repetition rate of 8: (LMO15/STO2)8. Epitaxial multilayer growth at high temperatures (900 °C) activates a selective inter-diffusion of La3+ and Sr2+ cations across the interfaces, which gives rise to Sr p-doping of the LMO and La n-doping of the STO layers. MC effects at the buried La1–xSrxMnO3/SrxLa1–xTiO3 (LSMO/SLTO) interfaces are probed by frequency, temperature and magnetic field dependent AC impedance spectroscopy. The technique is shown to be appropriate to account for the separate analysis of different resistance and capacitance contributions at the buried interfaces. As a result of the La/Sr inter-diffusion process, Schottky barriers are formed at the LSMO/SLTO interfaces, which give rise to massive MC of up to ≈ −200% in the out-of-plane film direction. The capacitance of the manganite-titanate LSMO/SLTO interfaces may be coupled indirectly to the resistance of the LSMO layers, because the Schottky space-charge layers and their capacitance can be modulated by varying the concentration of highly mobile charge carriers in the LSMO with a magnetic field.

The reversible phase transformation between B2 austenite phase and B19’ martensite phase is the governing mechanism behind the exciting active and passive capabilities of Nickel–Titanium (NiTi) knitted architectures. NiTi knitted architectures are manufactured from a monofilament fiber of originally-straight NiTi wire that is bent into an interlocking network of adjacent loops. Depending on the thermo-mechanical load path, NiTi knitted architectures can provide excellent isothermal energy-absorption using the superelastic effect (SE) or function as large-deformation actuators that respond to thermal inputs using the shape memory effect (SME). The magnitude of NiTi knitted architecture characteristic performance metrics is dependent on the ability of the knitted architecture to undergo the reversible phase transformation, which is a function of the material stresses, strains, and temperature. This research quantifies the NiTi knitted architecture austenite phase fraction of the highly stressed filament surface in X-ray diffraction experiments as a function of the measurement position on the knitted loop and applied thermo-mechanical loading conditions. A Bruker D8 Discover 2D micro-diffractometer was equipped with a custom tensile straining- and temperature-control device. The Direct Comparison Method was employed to derive the austenite phase fraction from the X-ray diffraction patterns. This research establishes novel in-situ strain- and temperature-control X-ray micro-diffraction experiments and provides understanding of the governing deformation modes in NiTi knitted architectures.

The magnetic-field-tuned quantum superconductor-insulator transitions of disordered amorphous indium oxide films are a paradigm in the study of quantum phase transitions, and exhibit power-law scaling behavior. For superconducting indium oxide films with low disorder, such as the ones reported on here, the high-field state appears to be a quantum-corrected metal. Resistance data across the superconductor-metal transition in these films are shown here to obey an activated scaling form appropriate to a quantum phase transition controlled by an infinite randomness fixed point in the universality class of the random transverse-field Ising model. Collapse of the field-dependent resistance vs. temperature data is obtained using an activated scaling form appropriate to this universality class, using values determined through a modified form of power-law scaling analysis. This exotic behavior of films exhibiting a superconductor-metal transition is caused by the dissipative dynamics of superconducting rare regions immersed in a metallic matrix, as predicted by a recent renormalization group theory. The smeared crossing points of isotherms observed are due to corrections to scaling which are expected near an infinite randomness critical point, where the inverse disorder strength acts as an irrelevant scaling variable., Comment: 8 pages, 6 figures

We summarize recent studies of oxide ion dynamics in ionically conducting defect pyrochlores of general formulae Ln 2 Ti 2 − y Zr y O 7 . Unit cell volume, structural disorder, and ion–ion interactions, are all relevant in determining ion hopping probability and thus the mobility of oxide ions at high temperatures. At enough low temperatures ion hopping is scarce and oxide ion dynamics are restricted to local displacements within the cage.

Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402-1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBaCuO (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics., A.M.G. was supported partially by US National Science Foundation Award DMR-1420013 through the Minnesota Materials Research Science and Engineering Center and by US National Science Foundation Award DMR-1209578. J.G.-B. acknowledges support from the Ministerio de Economía, Industria y Competitividad (MINECO) through the Ramon y Cajal Program and through MINECO Award PCIN-2013-061. Calculations were performed using computer resources from Genci Grand Équipement National de Calcul Intensif under Centre Informatique National de l’Enseignement Suprieur Grants c2015097211 and c2016097211. Work at Universidad Complutense de Madrid was supported by the Spanish MINECO through Grants MAT2014-52405-C02-01 and Consolider Ingenio 2010-CSD2009-00013 (Imagine) and by Comunidad Autonoma de Madrid (CAM) through Grant CAM S2013/MIT-2740. The SpLine beamline is supported financially by the Spanish MINECO and Consejo Superior de Investigaciones Cientificas under Grant PIE 2010 6 OE 013. P.S. acknowledges the support from Fundação de Amparo à Pesquisa do Estado de São Paulo Projects 2012/18397-2 and 2013/12537-9.

The long-chain members of the lead(II) alkanoate series or soaps, from octanoate to octadecanoate, have been thoroughly characterized by means of XRD, PDF analysis, DSC, FTIR, ssNMR and other techniques, in all their phases and mesophases. The crystal structures at room temperature of all of the members of the series are now solved, showing the existence of two polymorphic forms in the room temperature crystal phase, different to short and long-chain members. Only nonanoate and decanoate present both forms, and this polymorphism is proven to be monotropic. At higher temperature, these compounds present a solid mesophase, defined as rotator, a liquid crystal phase and a liquid phase, all of which have a similar local arrangement. Since some lead(II) soaps appear as degradation compounds in oil paintings, the solved crystal structures of lead(II) soaps can now be used as fingerprints for their detection using X-ray diffraction. Pair distribution function analysis on these compounds is very similar in the same phases and mesophases for the different members, showing the same short range order. This observation suggests that this technique could also be used in the detection of these compounds in disordered phases or in the initial stages of formation in paintings, Partial support of this research by the DGICYT of the Spanish ‘‘Ministerio de Educacio ́ n y Ciencia’’ (Grants in aid for Scientific Research CTQ2008-06328, CTQ2013-41781-P and CTQ2015- 67755-C2-1-R) is gratefully acknowledged. LG acknowledges financial support provided by CSIC. The authors wish to thank the beamlines BM25-Spline and ID31 (ESRF, Grenoble, France), I711 (Max II ring, MAX IV Laboratory, Lund, Sweden), the Center of Scientific Instrumentat ion at the University Complutense of Madrid (CAI of XRD, Centro de Asistencia a la Investigacio ́ n), and the Laboratory for Crystallographic Studies (IACT, CSIC-UGR), and their staff, for the use of their technical facilities and help.

Ultrathin YBa2Cu3O7−x (YBCO) films were grown on SrTiO3 (STO) substrates using the technique of high-pressure oxygen sputtering. Films were then incorporated in a field effect transistor configuration, which facilitated the control of superconductivity by electrostatic charging. While devices using STO as both the substrate and gate dielectric have produced only relatively small shifts in film electrical properties, very large changes can be realized using an electric double layer transistor configuration employing the ionic liquid DEME-TFSI as the dielectric. By depleting holes an electrostatically tuned superconductor insulator transition was studied using a finite size scaling analysis. The breakdown of scaling at the lowest temperatures suggests the presence of a mixed insulator/superconductor phase separating the two ground states. Further depletion of holes resulted in a change of the majority carriers from holes to electrons and the emergence of what appeared to be very weak re-entrant superconductivity. Also by accumulating holes an underdoped film was tuned into the overdoped regime. A two-step mechanism for electrostatic doping was revealed. Hall effect measurements suggested the presence of an electronic phase transition or a change in the Fermi surface as a function of doping near optimal doping.

Progress in understanding and exploiting the properties of complex oxide heterostructures requires advances in stateof- the-art growth and characterization techniques for these materials. Currently, atomic control of their synthesis is demonstrably inferior to that of their semiconductor counterparts, [ 1 ] despite recent progress for example in creating a high mobility two-dimensional electron gas in semiconducting ZnO [ 2 , 3 ] and in exploring novel interface effects in perovskites. [ 4 ] This superiority in growth control can be attributed in part to the development of quantitative, in situ refl ection high-energy electron diffraction (RHEED) possible in the UHV environment typical of semiconductor fi lm growth. [ 5 ] Oxides with the perovskite structure (chemical formula ABO 3 ) have attracted enormous interest as they display a wide range of exotic properties driven by strong spin-charge-lattice coupling, [ 6 ] such as quantum critical behavior in superconducting cuprates, colossal magnetoresistance in phase-separated manganites, and magnetoelectric coupling in BiFeO 3 . This coupling underlies the strong response of the electronic structure to small distortions of the BO 6 octahedra away from simple cubic coordination, distortions driven either by a Jahn-Teller (J-T) mechanism (removing energy level degeneracy by symmetry reduction) or by octahedral rotations to accommodate imperfect packing within the cubic unit cell that depends on cationic radii. These distortions are signifi cantly infl uenced in a stochastic way by disorder, unavoidably introduced by random A-site doping [ 7 ] or off-stoichiometry (ratio A:B ? 1, or oxygen vacancies) often seen in epitaxial films. In the search for novel electronic properties at interfaces, additional defect mechanisms such as cation intermixing and segregation must be addressed and their precise distribution near the interface known. Ultimately, identifying new electronic properties will depend critically on eliminating these forms of disorder and defects, or precisely controlling them if desired, through atomic design. Here we report evidence of signifi cant improvements in the atomic design of perovskite interfaces made possible by advances in in situ RHEED control of surfaces that exploit the detection of the characteristic octahedral distortions in the surface layer as it is being deposited. This method allows optimization of the phase diagram versus doping of films, and eliminates intermixing and anomalous lattice dilations at interfaces that have previously been observed. Careful structural analysis shows an unusual evolution of octahedral distortions including both J-T type and rotations near the interface not seen in bulk. These new results should be included in electronic structure calculations modeling the properties of real heterointerfaces.

Using X-ray absorption spectroscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for charge transfer at the interface between the Mott insulators Sm2CuO4 and LaFeO3 is obtained. As a consequence of the charge transfer, the Sm2CuO4 is doped with electrons and thus epitaxial Sm 2CuO4/LaFeO3 heterostructures become metallic. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., Work at UCM supported by Spanish MICINN Grant MAT 2011 27470, Consolider Ingenio CSD2009-00013 (IMAGINE), CAM S2009-MAT 1756 (PHAMA) and ERC starting Investigator Award, grant #239739 STEMOX. R.S. wishes to acknowledge the Ministerio de Ciencia e Innovación (MICINN) for granting a Ramon y Cajal Fellowship.

Towards cooler solid oxide fuel cells: Disorder and dimensionality (see picture) play an important role in determining ion mobility of bulk and artificially nanolayered materials and should be considered in the design of new electrolytes with enhanced conductivity. Reducing the operation temperature of solid oxide fuel cells is a major challenge towards their widespread use for power generation. This has triggered an intense materials research effort involving the search for novel electrolytes with higher ionic conductivity near room temperature. Two main directions are being currently followed: the use of doping strategies for the synthesis of new bulk materials and the implementation of nanotechnology routes for the fabrication of artificial nanostructures with improved properties. In this paper, we review our recent work on solid oxide fuel cell electrolyte materials in these two directions, with special emphasis on the importance of disorder and reduced dimensionality in determining ion conductivity. Substitution of Ti for Zr in the A2Zr2−yTiyO7 (A=Y, Dy, and Gd) series, directly related to yttria stabilized zirconia (a common fuel cell electrolyte), allows controlling ion mobility over wide ranges. In the second scenario we describe the strong enhancement of the conductivity occurring at the interfaces of superlattices made by alternating strontium titanate and yttria stabilized zirconia ultrathin films. We conclude that cooperative effects in oxygen dynamics play a primary role in determining ion mobility of bulk and artificially nanolayered materials and should be considered in the design of new electrolytes with enhanced conductivity.

We investigate the effect of cation size in the dc activation energy needed for oxygen ion conductivity, Edc, in highly disordered pyrochlore-type ionic conductors A2B2O7. Twenty compositions of general formula Ln2Zr2-yTiyO7 (Ln = Y, Dy and Gd) and Gd2-yLayZr2O7, were prepared by mechanical milling and their electrical properties measured by using impedance spectroscopy at different temperatures. We also evaluate, by using Ngai’s Coupling Model, the effect of cation radii RA and RB, on the microscopic potential-energy barrier, Ea, that oxygen ions encounter when jumping into neighboring vacant sites. We find that for a fixed B-site cation radius RB, both activation energies decrease with increasing A-site cation size, RA, as a consequence of the increment in the unit cell volume. In contrast, and for a given RA size, the dc activation energy Edc of the Ln2Zr2-yTiyO7 series increases when the average RB size increases. The latter behavior is explained in terms of the enhanced interactions among mobile oxygen ions as the structural disorder increases when RB approaches RA.

We report large magnetoresistance in ferromagnet/superconductor/ferromagnet structures made of La 0.7 Ca 0.3 MnO 3 and YBa 2 Cu 3 O 7 at temperatures along the resistive transition. We find that the magnetoresistance phenomenon is independent on the orientation of electric current versus field. Furthermore, the effect is also independent on the sweep rate of the magnetic field. This excludes interpretations in terms of spontaneous vortices or anisotropic magnetoresistance of the ferromagnetic layers and supports the view that the magnetoresistance phenomenon originates at the spin-dependent transport of quasiparticles transmitted from the ferromagnetic electrodes into the superconductor.

Lead(II) alkanoates, from hexanoate to dodecanoate, have been analyzed by means of XRD, optical microscopy, DSC, FTIR, and electric spectroscopy. Four different phases have been identified, corresponding to the three thermal transitions measured by DSC: two of them solid (crystal and “intermediate” phases), and another two fluid (neat phase and isotropic liquid). Powder crystal XRD data indicate that the samples present a bilayered structure. The analysis of the (00l) spacing dependence with temperature in the three ordered phases strongly points to the intermediate phase to be a rotator phase. Optical microscopy and FTIR versus temperature also confirm a structural change from the crystal to the intermediate phase and its solid-state nature. Electrical conductivity maps the thermal transitions of the samples and shows a high ionic conductivity in the intermediate phase, which does not depend much on the carbon chain length. The high conductivity values (3 orders of magnitude higher in comparison with th...

Finding more efficient ways of exploring the doping phase diagrams of high-temperature superconductors as well as probing the fundamental properties of these materials are essential ingredients for driving the discovery of new materials. We use a doping technique involving gating with ionic liquids to systematically and continuously tune the ${T}_{c}$ of superconducting ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4+x}$ thin films. We probe both the transport properties and the penetration depth of these samples and find that Homes scaling ${\ensuremath{\lambda}}^{\ensuremath{-}2}\ensuremath{\propto}\ensuremath{\sigma}{T}_{c}$ is obeyed, consistent with these materials being in the dirty limit. This result is independent of the precise mechanism for the gating process as all of the parameters of the scaling relationship are determined by direct measurements on the films.

Different compositions in a solid solution of general formula Dy2(Ti1−yZry)2O7, showing high oxygen ion conductivity, have been successfully prepared at room temperature via mechanochemical synthesis. Stoichiometric mixtures of the constituent oxides were dry milled together in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by X-ray diffraction and revealed that, in all cases and after milling for 19 h, the powder mixtures consisted of a single phase. Electrical properties were measured on sintered pellets as a function of frequency, temperature and zirconium content, revealing an increase in conductivity of more than one order of magnitude for y ⩾ 0.4 , which, as observed in the similar Y2(Ti1−yZry)2O7, has been related with the onset of disordering of the anion sublattice. Despite increasing structural disorder with increasing Zr content, conductivity remains almost constant for y > 0.6 , reaching a maximum value of ∼5×10−3 for Dy2Zr2O7 at 900 °C.

Several compositions within the Gd{sub 2}(Sn{sub 1-y}Zr{sub y}){sub 2}O{sub 7} solid solution with a pyrochlore-type of structure, have been prepared at room temperature in a planetary ball mill starting from stoichiometric mixtures of the constituent oxides, SnO{sub 2}, ZrO{sub 2} and Gd{sub 2}O{sub 3}. Phase evolution in the powder mixtures as a function of composition and milling time was followed by X-ray diffraction (XRD) finding out that after 18h, every mixture consist of a single phase. Mechanically activated chemical reaction takes place after an intial step of particle size refinement and polymorphic transformation of C-Gd{sub 2}O{sub 3}. We have performed Impedance Spectroscopy measurements to investigate oxygen ion dynamics in the series and conclude that Zr substitution for Sn hardly modifies the importance of ion-ion correlations in the oxygen diffusion process. We also estimate from conductivity measurements the value of the microscopic activation energy needed for independent ion hopping, which is found to be 0.56+/-0.06eV, independent of Zr content.

We analyze ion dynamics in the oxygen ion conductor Gd2Ti2−yZryO7 by impedance spectroscopy measurements. We find that electrical conductivity relaxation is well described by stretched exponentials of the form Φ(t) = exp(−(t/τ)1−n), with the fractional exponent n increasing systematically with Zr content. Increasing Zr content also leads to an increase in the activation energies for long-range ion diffusion from 0.7 to 1.0 eV. These results are explained in terms of the enhanced cooperativity in oxygen ion dynamics when increasing the concentration of mobile oxygen vacancies with Zr content.

6 páginas, 9 figuras., [ES] En este trabajo se estudia la influencia de la adición de un 10 % en volumen, de cromo en las propiedades mecánicas de aleaciones NI3Al-Cr procesadas por vía pulvimetalúrgica. Para ello se prepararon dos aleaciones: la primera, se obtuvo por molienda de polvo de composición Ni-20,9Al-8Cr-0,49B (% at.) y, a la segunda, se le añadió un 10 % en volumen de partículas de cromo, mediante un proceso de mezcla, previo al de molienda. Ambas, fueron consolidadas mediante compactación isostática en caliente (HIP) y, por último, se les aplicaron tratamientos térmicos para homogeneizar la microestructura. Los resultados experimentales han mostrado que el refuerzo de cromo tiene como efecto un importante aumento del límite elástico y de la resistencia. Así, el material reforzado presenta un límite elástico cercano a 1.300 MPa, a temperatura ambiente, frente a los 800 MPa que presenta el material sin reforzar, a la misma temperatura. En relación con las propiedades mecánicas de los materiales tratados térmicamente, se observa que ambos experimentan un acusado descenso de la ductilidad y de la resistencia máxima a la tracción., [EN] The mechanical properties of NI3Al-Cr reinforced with 10% in volume fraction of chromium particles produced by powder metallurgy have been studied. For this purpose, milled powders with composition of Ni-20.9Al-8Cr-0.49B (% at.) with and without the addition of 10% in volume fraction of chromium particles have been produced. Both alloys were consolidated by hot isostatic pressing (HIP). After HIP, heat treatment was applied to homogenize the microstructure. The chromium reinforcement has an important effect in the yield strength and ultimate strength increase. The reinforced alloy presents a yield strength of 1300 MPa at room temperature with respect to 800 MPa for the un-reinforced material. After heat treatment, the yield strength of both alloys does not change significantly. However, a decrease in ductility and ultimate tensile strength have been observed., Este trabajo ha sido financiado por el Ministerio de Educación y Cultura, proyecto MAT 2000- 1496.

We report on the dispersive ionic conductivity in Li0.5 − xNaxLa0.5TiO3 (0 ≤ x ≤ 0.5), where the number of available positions for the mobile Li ions is reduced by introducing immobile Na ions. At high frequency the conductivity is power law dependent with an exponent which increases as the number of accessible neighboring sites decreases. This result is quantitatively accounted for in terms of a one-parameter statistical microscopic model. We provide experimental and theoretical evidence for the importance of reduced dimensionality resulting from the blocked pathways in slowing down the dynamics of diffusing ions.

Presentamos un estudio de la conductividad ionica en las series Y_(2)Ti_(2-y)Zr_(y)O_(7) y Gd_(2)Ti_(2-y)Zr_(y)O_(7) (0≤y≤2) obtenidas por sintesis mecanoquimica. Se presenta un estudio de la dinamica de iones oxigeno en estos materiales mediante la tecnica de Espectroscopia de Admitancias. La variacion con el contenido en Zr de la conductividad dc y de su energia de activacion se interpreta en terminos del aumento tanto del numero de vacantes de oxigeno como del desorden en la estructura al aumentar el contenido en Zr.

We present electrical conductivity measurements of BIFEVOX Bi4V2-xFexO11-y (0≤x≤0.9; 0≤y≤1), in which V (IV) ions have been systematically substituted by Fe (III) ions. Conductivity shows a power law frequency dependence described by the form σ*(ω)=σdc[1+(jω/ωp)n], known as universal dynamic response. Conversely, the electric modulus shows asymmetric peaks, characterized by stretched exponentials relaxation functions in time domain of the form φ(t)=exp(-(t/τσ)β). β is determined by the degree of correlation in the ionic motion. It´s value, β=0.56±0.03, is almost independent of temperature and iron content. Increasing Fe content leads to an exponential decrease of the conductivity and to an increase of the activation energy of the conduction process from 0.20 to 0.97 eV. These results are discussed in terms of oxygen vacancy ordering upon Fe (III) substitution.Presentamos medidas de la conductividad eléctrica del sistema BIFEVOX Bi4V2-xFexO11-y (0≤x≤0.9; 0≤y≤1), en el que se realiza la sustitución de iones V (IV) por Fe (III) de forma sistemática. La conductividad muestra un comportamiento potencial con la frecuencia, descrito por σ*(ω)=σdc[1+(jω/ωp)n], y conocido como respuesta dieléctrica universal. Análogamente, el módulo eléctrico presenta picos asimétricos, cuya función de relajación en el dominio del tiempo puede describirse mediante exponenciales “estiradas” de la forma φ(t)=exp(-(t/τσ)β). β da cuenta del grado de correlación del transporte iónico, siendo su valor, β=0.56±0.03, casi independiente de la temperatura y del contenido en Fe. Con el aumento en el contenido de Fe, la conductividad disminuye exponencialmente y la energía de activación del proceso de conducción aumenta de 0.20 a 0.97 eV. Estos resultados se discuten en términos de la ordenación de vacantes oxígeno al dopar con Fe (III).

In this work we study the interfaces between the Mott insulator LaMnO3 (LMO) and the band insulator SrTiO3 (STO) in epitaxially grown superlattices with different thickness ratios and different transport and magnetic behaviors. Using atomic resolution electron energy-loss spectral imaging, we analyze simultaneously the structural and chemical properties of these interfaces. We find changes in the oxygen octahedral tilts within the LaMnO3 layers when the thickness ratio between the manganite and the titanate layers is varied. Superlattices with thick LMO and ultrathin STO layers present unexpected octahedral tilts in the STO, along with a small amount of oxygen vacancies. On the other hand, thick STO layers exhibit undistorted octahedra while the LMO layers present reduced O octahedral distortions near the interfaces. These findings are discussed in view of the transport and magnetic differences found in previous studies.

We report on the coherent growth of ultrathin YBa2Cu3O7 (YBCO) layers on SrTiO3 (STO) in YBCO/STO superlattices. The termination plane of the STO is TiO2 and the CuO chains are missing at the interface. Disorder (steps) at the STO interface cause alterations of the stacking sequence of the intra-cell YBCO atomic layers. Stacking faults give rise to antiphase boundaries which break the continuity of the CuO2 planes and depress superconductivity. We show that superconductivity is directly controlled by interface disorder outlining the importance of pair breaking and localization by disorder in ultrathin layers.

Using an electronic double layer transistor we have systematically studied the superconductor-to-insulator transition in La${}_{2}$CuO${}_{4+\ensuremath{\delta}}$ thin films grown by ozone-assisted molecular-beam epitaxy. We have confirmed the high crystalline quality of the cuprate films and have demonstrated the suitability of the electronic double layer technique to continuously vary the charge density in a system that is otherwise characterized by the presence of miscibility gaps. The transport and magnetotransport results highlight the role of electron-electron interactions in the mechanism of the transition due to the proximity of the Mott-insulating state.

We successfully tuned an underdoped ultrathin YBa2Cu3O(7-x) film into the overdoped regime by means of electrostatic doping using an ionic liquid as a dielectric material. This process proved to be reversible. Transport measurements showed a series of anomalous features compared to chemically doped bulk samples and a different two-step doping mechanism for electrostatic doping was revealed. The normal resistance increased with carrier concentration on the overdoped side and the high temperature (180 K) Hall number peaked at a doping level of p∼0.15. These anomalous behaviors suggest that there is an electronic phase transition in the Fermi surface around the optimal doping level.

We successfully tuned an underdoped ultrathin YBa2Cu3O(7-x) film into the overdoped regime by means of electrostatic doping using an ionic liquid as a dielectric material. This process proved to be reversible. Transport measurements showed a series of anomalous features compared to chemically doped bulk samples and a different two-step doping mechanism for electrostatic doping was revealed. The normal resistance increased with carrier concentration on the overdoped side and the high temperature (180 K) Hall number peaked at a doping level of p∼0.15. These anomalous behaviors suggest that there is an electronic phase transition in the Fermi surface around the optimal doping level.

The electrical transport properties of ultrathin YBa₂Cu₃O(7-x) films have been modified using an electric double layer transistor configuration employing an ionic liquid. A clear evolution from superconductor to insulator was observed in nominally 7 unit-cell-thick films. Using a finite size scaling analysis, curves of resistance versus temperature, R(T), over the temperature range from 6 to 22 K were found to collapse onto a single scaling function, which suggests the presence of a quantum critical point. However, the scaling fails at the lowest temperatures indicating the possible presence of an additional phase between the superconducting and insulating regimes.

We report on the magnetic coupling of La0.7Sr0.3MnO3 layers through SrTiO3 spacers in La0.7Sr0.3MnO3/SrTiO3 epitaxial heterostructures. Combined aberration-corrected microscopy and electron-energy-loss spectroscopy evidence charge transfer to the empty conduction band of the titanate. Ti d electrons interact via superexchange with Mn, giving rise to a Ti magnetic moment as demonstrated by x-ray magnetic circular dichroism. This induced magnetic moment in the SrTiO3 controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm.

The electrical transport properties of ultrathin YBa₂Cu₃O(7-x) films have been modified using an electric double layer transistor configuration employing an ionic liquid. A clear evolution from superconductor to insulator was observed in nominally 7 unit-cell-thick films. Using a finite size scaling analysis, curves of resistance versus temperature, R(T), over the temperature range from 6 to 22 K were found to collapse onto a single scaling function, which suggests the presence of a quantum critical point. However, the scaling fails at the lowest temperatures indicating the possible presence of an additional phase between the superconducting and insulating regimes.

Colossal ionic conductivity was recently discovered in YSZ/SrTiO_(3) multilayers and was explained in terms of strain- and interface-enhanced disorder of the O sublattice. In the present paper we use a combination of scanning transmission electron microscopy and electron energy loss spectroscopy (EELS) and theoretical EELS simulations to confirm the presence of a disordered YSZ O sublattice in coherent YSZ/SrTiO_(3) multilayers. O K-edge fine structure simulated for the strained disordered O sublattice phase of YSZ possesses blurred-out features compared to that of ordered cubic bulk YSZ, and experimental EELS fine structure taken from the strained YSZ of coherent YSZ/SrTiO_(3) thin films is similarly blurred out. Elemental mapping is shown to be capable of resolving ordered YSZ O sublattices. Elemental mapping of O in the coherent YSZ/STO multilayers is presented in which the O sublattice is seen to be clearly resolved in the STO but blurred out in the YSZ, indicating it to be disordered. In addition, we present imaging and EELS results which show that strained regions exist at the incoherent interfaces of YSZ islands in STO with blurred out fine structure, suggesting these incoherent regions may also support high ionic conductivities. Recently, Cavallaro et al. reported electronic conductivities in samples of incoherent disconnected islands embedded in STO that are similar to the islands described herein. The presence of a region of O depleted STO at the interface with incoherent YSZ islands is revealed by EELS elemental mapping, implying the n-type doping of STO/YSZ nanocomposites with disconnected incoherent YSZ islands.

Heterostructures combining transition metal oxides, as compared to other materials, are able to accommodate very large amounts of epitaxial strain without breaking into islands or structural domains. Coherently strained interfaces are an interesting playground for the search of materials with enhanced ion diffusivities, of interest in devices for energy generation and storage. In this work we highlight the importance of the interface structure of highly strained YSZ/STO superlattices in determining an enhancement of their ionic conductivity. We show the role of growth orientation in controlling the structure and morphology of the interface. Results of density functional theory calculations are discussed, showing that the incompatibility of the oxygen positions at the interface planes plays a key role in stabilizing the high values of ionic conductivities. Heterostructures combining transition metal oxides are an interesting playground for the search of materials with enhanced ion diffusivities, of interest in devices for energy generation and storage. In particular, the control of the interface structure of highly strained YSZ/SrTiO3 superlattices allows changing ion conductivity in a wide range. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., Work at UCM supported by Spanish MICINN Grant MAT 2008 06517, Consolider Ingenio CSD2009-00013 (IMAGINE), CAM S2009-MAT 1756 (PHAMA) and the European Research Council Starting Investigator Award "STEMOX". Work at ORNL was supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Research at Vanderbilt was supported in part by the U.S. Department of Energy Grant DE-FG02-09ER46554 and the McMinn Endowment. R. S. & N.M.N. Spanish thank MICINN for granting Ramon y Cajal Fellowships. O.J.D thanks JCCM for a post doc Fellowship.