Publications (18)113 Total impact
-
Dataset: F.Y. Bruno et al. Adv.Mater. 25 (2013) p.1468 Supporting Information
-
Article: Electron Doping by Charge Transfer at LaFeO3/Sm2CuO4 Epitaxial Interfaces
[show abstract] [hide abstract]
ABSTRACT: In this paper, the structural and electronic properties of heterostructures involving Sm2CuO4 (SCO) and LaFeO3 (LFO) will be studied. SCO is a Mott insulator that becomes superconducting upon replacing Sm3+ ions with Ce4+ to form Sm2−xCexCuO4 , an electron doped HTSC. LFO is also a Mott insulator with its chemical potential being approximately 1 eV above the chemical potential of SCO. The gap in both of these materials is of the charge-transfer (CT) type, i.e. the energy difference Δ between the O–2p band and the upper Hubbard band is smaller than the energy difference U between the lower and upper Hubbard bands. The transfer of charge involving CT Mott insulators provides an interesting framework, which to our knowledge has not been examined before. Moreover, LFO is a good candidate to transfer electrons from its O 2p valence band to the CuO 2 d-like upper Hubbard band of the SCO. Since La 1−x Sr x FeO 3 remains insulating and antiferromagnetic even if doped with holes up to x < 0.7, this state should not be detrimental to a possible superconducting state if an interface with SCO is made. Here, it will be shown that it is indeed possible to obtain a doped n-type material at the SCO/LFO interface of two CT insulators, which displays metallic behavior in the temperature range of 150–300 K.Advanced Materials 03/2013; 25:1468. · 13.88 Impact Factor -
Article: Caracterización eléctrica de fronteras de grano en conductores iónicos mediante medidas de espectroscopia de impedancias en un bicristal
[show abstract] [hide abstract]
ABSTRACT: Here we show impedance spectroscopy measurements on a bicrystal of the ionically conducting yttria stabilized zirconia (YSZ). By using micrometer sized electrodes it is possible to measure ionic transport perpendicular to a single grain boundary, and characterize its electrical properties. We are thus able to obtain the microscopic parameters that determine the charge distribution at the grain boundary and the ionic transport through it, as the potential energy barrier DF = 0.35±0.01 V at 275ºC, and the space charge layer thickness l* = 5±1 Å. These values are significantly different from those previously obtained in polycrystalline ceramic samples of the same material, and show much better agreement with the values predicted by the Mott-Schottky model for the charge distribution and ionic transport through the grain boundary.Boletin de la Sociedad Espanola de Ceramica y Vidrio 01/2012; 51:13. · 0.43 Impact Factor -
Article: Tailoring interface structure in highly strained YSZ/STO heterostructures.
[show abstract] [hide abstract]
ABSTRACT: 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 inter- faces 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 conduc- tivity. 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 inter- face planes plays a key role in stabilizing the high values of ionic conductivities.Advanced Materials 11/2011; 23(44):5268-74. · 13.88 Impact Factor -
Article: Tailoring Interface Structure in Highly Strained YSZ/STO Heterostructures
[show abstract] [hide abstract]
ABSTRACT: 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.Advanced Materials 11/2011; 23:5268. · 13.88 Impact Factor -
Article: Electronic and magnetic reconstructions in La0.7Sr0.3MnO3/SrTiO3 heterostructures: a case of enhanced interlayer coupling controlled by the interface.
[show abstract] [hide abstract]
ABSTRACT: 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.Physical Review Letters 04/2011; 106(14):147205. · 7.37 Impact Factor -
Article: All-manganite tunnel junctions with interface-induced barrier magnetism.
Advanced Materials 11/2010; 22(44):5029-34. · 13.88 Impact Factor -
Article: Spin and orbital Ti magnetism at LaMnO3/SrTiO3 interfaces
Nature Communications 09/2010; 1:82. · 7.40 Impact Factor -
Article: Spin and orbital Ti magnetism at LaMnO3/SrTiO3 interfaces.
[show abstract] [hide abstract]
ABSTRACT: In systems with strong electron-lattice coupling, such as manganites, orbital degeneracy is lifted, causing a null expectation value of the orbital magnetic moment. Magnetic structure is thus determined by spin-spin superexchange. In titanates, however, with much smaller Jahn-Teller distortions, orbital degeneracy might allow non-zero values of the orbital magnetic moment, and novel forms of ferromagnetic superexchange interaction unique to t(2g) electron systems have been theoretically predicted, although their experimental observation has remained elusive. In this paper, we report a new kind of Ti(3+) ferromagnetism at LaMnO(3)/SrTiO(3) epitaxial interfaces. It results from charge transfer to the empty conduction band of the titanate and has spin and orbital contributions evidencing the role of orbital degeneracy. The possibility of tuning magnetic alignment (ferromagnetic or antiferromagnetic) of Ti and Mn moments by structural parameters is demonstrated. This result will provide important clues for understanding the effects of orbital degeneracy in superexchange coupling.Nature Communications 01/2010; 1:82. · 7.40 Impact Factor -
Article: Synthesis of Li<sub>1+x</sub>M<sup>III</sup><sub>x</sub>Ti<sub>2-x</sub>(PO<sub>4</sub>)<sub>3</sub> with nasicon structure, using sol-gel methods. Study of the relationship microstructure – electrical properties
[show abstract] [hide abstract]
ABSTRACT: Compounds of formula Li1+xMIIIxTi2-x(PO4)3 with MIII = Cr, Fe and x = 0 and 0.05 have been prepared at soft temperatures using the Pechini synthesis method, based on sol-gel chemistry. The structural and microstructural characterization by X-ray diffraction and Scanning Electron Microscopy (SEM), shows that all of them crystallize in a NASICON-type structure with similar lattice parameters. Doping with Fe and Cr, causes an increase of the density of the samples after sinterization what clearly improves the ionic conductivity of the original material, LiTi2(PO4)3 until values of 9x10-4 S cm-1 at room temperature in the chromium-doped material.Haciendo uso de la química sol-gel, se han preparado ortofosfatos de composición LiTi2(PO4)3 y Li1.05(Cr/Fe)0.05Ti1.95(PO4)3 a temperaturas moderadas mediante el método Pechini. Estas fases han sido caracterizadas estructural y microestructuralmente por difracción de rayos X de polvo y microscopía electrónica de barrido (SEM), encontrándose que todas cristalizan en una estructura tipo NASICON, con parámetros de red muy similares. El dopaje con Fe y Cr permite aumentar la densidad de las muestras en la sinterización, mejorando de forma apreciable su conductividad iónica. Se ha observado un incremento de hasta cuatro órdenes de magnitud en la conductividad a temperatura ambiente obteniéndose una energía de activación de 0.29 eV para el material dopado con Cr.Boletín de la Sociedad Española de Cerámica y Vidrio. 01/2010; -
Article: Colossal ionic conductivity at interfaces of epitaxial ZrO2:Y2O3/SrTiO3 heterostructures.
[show abstract] [hide abstract]
ABSTRACT: The search for electrolyte materials with high oxygen conductivities is a key step toward reducing the operation temperature of fuel cells, which is currently above 700 degrees C. We report a high lateral ionic conductivity, showing up to eight orders of magnitude enhancement near room temperature, in yttria-stabilized zirconia (YSZ)/strontium titanate epitaxial heterostructures. The enhancement of the conductivity is observed, along with a YSZ layer thickness-independent conductance, showing that it is an interface process. We propose that the atomic reconstruction at the interface between highly dissimilar structures (such as fluorite and perovskite) provides both a large number of carriers and a high-mobility plane, yielding colossal values of the ionic conductivity.Science 09/2008; 321(5889):676-80. · 31.20 Impact Factor -
Article: Ion dynamics under pressure in an ionic liquid.
[show abstract] [hide abstract]
ABSTRACT: We investigate ion dynamics under pressure in the ionic liquid 1-butyl-1-methylpyrrolidinium bis[oxalate]borate (BMP-BOB) by conductivity relaxation measurements in the temperature range 123-300 K and varying pressures from 0.1 MPa up to 0.5 GPa. We report on the influence of pressure on the relaxation times and on the spectral shape of the conductivity relaxation process. We also analyze the pressure dependence of the glass transition temperature and find that the dynamic response under pressure in this ionic liquid shows remarkable similarities to nonionic glass formers. The main relaxation process shows temperature-pressure superposition while a secondary relaxation process, very weakly depending on pressure, is observed. The spectral shape of the main relaxation broadens with increasing pressure or decreasing temperature, but is found to be the same when the relaxation time is the same, independently of the particular pressure and temperature values.The Journal of Physical Chemistry B 04/2008; 112(10):3110-4. · 3.70 Impact Factor -
Article: Síntesis mediante química sol gel de compuestos Li1+xMiiixTi2-x(PO4)3 con estructura tipo Nasicon. Estudio de la relación microestructura-propiedades eléctricas
[show abstract] [hide abstract]
ABSTRACT: Haciendo uso de la química sol-gel, se han preparado ortofosfatos de composición LiTi2(PO4)3 y Li1.05(Cr/Fe)0.05Ti1.95(PO4)3 a temperaturas moderadas mediante el método Pechini. Estas fases han sido caracterizadas estructural y microestructuralmente por difracción de rayos X de polvo y microscopía electrónica de barrido (SEM), encontrándose que todas cristalizan en una estructura tipo NASICON, con parámetros de red muy similares. El dopaje con Fe y Cr permite aumentar la densidad de las muestras en la sinterización, mejorando de forma apreciable su conductividad iónica. Se ha observado un incremento de hasta cuatro órdenes de magnitud en la conductividad a temperatura ambiente obteniéndose una energía de activación de 0.29 eV para el material dopado con CrBoletín de la Sociedad Española de Cerámica y Vidrio, ISSN 0366-3175, Vol. 49, Nº. 1, 2010 (Ejemplar dedicado a: Electrocerámica: IX Reunión Nacional (Leganés 28-30 junio de 2009)), pags. 41-46. -
Article: All-Manganite Tunnel Junctions with Interface-Induced Barrier Magnetism
-
Article: Electronic and Magnetic Reconstructions in La(0.7)Sr(0.3)MnO(3)/SrTiO(3) Heterostructures: A Case of Enhanced Interlayer Coupling Controlled by the Interface
[show abstract] [hide abstract]
ABSTRACT: We report on the magnetic coupling of La(0.7)Sr(0.3)MnO(3) layers through SrTiO(3) spacers in La(0.7)Sr(0.3)MnO(3)/SrTiO(3) 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 SrTiO(3) controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm.PHYSICAL REVIEW LETTERS. 106(14). -
Article: Spin and orbital Ti magnetism at LaMnO(3)/SrTiO(3) interfaces
[show abstract] [hide abstract]
ABSTRACT: In systems with strong electron-lattice coupling, such as manganites, orbital degeneracy is lifted, causing a null expectation value of the orbital magnetic moment. Magnetic structure is thus determined by spin-spin superexchange. In titanates, however, with much smaller Jahn-Teller distortions, orbital degeneracy might allow non-zero values of the orbital magnetic moment, and novel forms of ferromagnetic superexchange interaction unique to t(2g) electron systems have been theoretically predicted, although their experimental observation has remained elusive. In this paper, we report a new kind of Ti(3+) ferromagnetism at LaMnO(3)/SrTiO(3) epitaxial interfaces. It results from charge transfer to the empty conduction band of the titanate and has spin and orbital contributions evidencing the role of orbital degeneracy. The possibility of tuning magnetic alignment (ferromagnetic or antiferromagnetic) of Ti and Mn moments by structural parameters is demonstrated. This result will provide important clues for understanding the effects of orbital degeneracy in superexchange coupling.NATURE COMMUNICATIONS. 1. -
Article: Transport, electronic, and structural properties of nanocrystalline CuAlO_ {2} delafossites
[show abstract] [hide abstract]
ABSTRACT: This work reports on the effect of grain size on the electrical, thermal, and structural properties of CuAlO2 samples obtained by solid-state reaction combined with ball milling. Electrical characterization made in microcrystalline and nanocrystalline samples shows that the electrical conductivity decreases several orders of magnitude for the nanocrystalline samples, and, in addition, there is a large discrepancy between the activation energies associated to thermoelectric power ES. The study of the Cu K-edge x-ray absorption spectra of the CuAlO2 samples shows that the local structure around Cu is preserved after the sintering process, indicating that the observed behavior of the electrical conductivity is of intrinsic origin. Complex conductivity measurements as a function of frequency allow us to discard grain-boundaries effects on the electrical transport. Thus, the changes in σ(T) and S(T) are interpreted in terms of charge localization in the framework of small polarons. This is in agreement with the analysis of the near-edge region of the absorption spectra, which indicates that sintering favors the Cu-O hybridization. As a consequence, oxygen atoms progressively lose their capability of trapping holes, and the electrical conductivity is also enhanced.Phys. Rev. B. 83(4). -
Article: Ionic conductivity of nanocrystalline yttria-stabilized zirconia: Grain boundary and size effects
[show abstract] [hide abstract]
ABSTRACT: We report on the effect of grain size on the ionic conductivity of yttria-stabilized zirconia samples synthesized by ball milling. Complex impedance measurements, as a function of temperature and frequency are performed on 10 mol % yttria-stabilized zirconia nanocrystalline samples with grain sizes ranging from 900 to 17 nm. Bulk ionic conductivity decreases dramatically for grain sizes below 100 nm, although its activation energy is essentially independent of grain size. The results are interpreted in terms of a space-charge layer resulting from segregation of mobile oxygen vacancies to the grain-boundary core. The thickness of this space-charge layer formed at the grain boundaries is on the order of 1 nm for large micron-sized grains but extends up to 7 nm when decreasing the grain size down to 17 nm. This gives rise to oxygen vacancies depletion over a large volume fraction of the grain and consequently to a significant decrease in oxide-ion conductivity.Phys. Rev. B. 81(18).
Top Journals
Institutions
-
2008–2011
-
Complutense University of Madrid
- Departamento de Física Aplicada III (Electricidad y Electrónica)
Madrid, Madrid, Spain
-
