Reducing the operating temperature in the 500-750 • C, is one of the major targets in present SOFC research 1,2 , and it is also a requisite for the development of miniaturized SOFCs for portable power supply 3,4 . Improving the electrolyte performance for intermediate-temperature operation can be achieved by reducing the electrolyte thickness 5,6 , and by using alternative materials to yttria-stabilized zirconia with a larger ionic conductivity in the intermediate temperature range 7 . With respect to the oxygen-ion conductors conventionally used in SOFCs, electrolytes based on high-temperature proton conductors (HTPCs) take advantage of their lower activation energy for charge transport 8 and of water formation at the cathode side 9,10 , thereby resulting in suitable conductivity in the intermediate temperature range and avoiding fuel dilution with water.Among HTPCs, Y-doped barium cerate (BCY) electrolytes have shown rather high protonic conductivity (10 −2 S cm −1 at 600 • C; ref. 11), although BCY strongly reacts with CO 2 (ref. 12) and water vapour 13 , hindering technological applications. On the other hand, despite a very good chemical stability of Y-doped barium zirconate (BZY) under fuel-cell operating environments, the total proton conductivity of BZY sintered pellets is generally significantly lower (about 10 −3 S cm −1 at 600 ; refs 14,15). This is due to the poor sinterability of BZY (ref. 16), together with the poor conducting properties of BZY grain boundary regions 17 . Scattered conductivity values for BZY samples are reported in the literature, and mostly depend on the processing parameters (see Supplementary Fig. S1).However, about a decade ago electrochemical impedance spectroscopy (EIS) measurements at temperatures below 200• C, that is, in the temperature range where impedance spectra allowed separation of the bulk and the grain boundary contribution,

Linear dichroism (LD) in x -ray absorption, diffraction, transport and magnetization measurements on thin La 0.7 Sr 0.3 MnO 3 films grown on different substrates, allow identification of a peculiar interface effect, related just to the presence of the interface. We report the LD signature of preferential 3d-e g (3z 2 -r 2 ) occupation at the interface, suppressing the double exchange mechanism.This surface orbital reconstruction is opposite to that favored by residual strain and is independent of dipolar fields, the chemical nature of the substrate and the presence of capping layers.Interfaces between perovskite oxides display unexpected properties. The roles of chemistry, polarization and strain may be singled out by selective experiments, e.g.Ref.[11], where an engineered interface obtained by intercalating two LMO unit cells (u.c.) between the LSMO and the STO has been shown to recover the LSMO bulk properties even at room temperature. The role of strain on preferential orbital occupation in transition metal oxides has been widely studied [12]. The anisotropy of d-orbitals influences the electron correlation effects in an orbital direction-dependent manner, thus giving rise to the anisotropy of the electron-transfer and eventually destroying the DE order of unstrained half-metallic LSMO (Fig.1, center). The strain effect on orbital physics can be understood on the basis of the experimental phase diagram proposedby Konishi et al.,[ 13] and explained theoretically by Fang et al.[14]. Spin ordering in strained manganite is influenced by orbital ordering and several anti-ferromagnetic (AF) insulating JahnTeller distorted phases are observed: the strain induced elongation or compression of the MnO 6 octahedra leads to crystal field splitting of the e g levels, lowering either i) the (3z 2 -r 2 ) state which favors the C -type AF structure (Fig.1, left) or ii) the (x 2 -y 2 ) state which stabilizes the A -type structure ( Fig.1, right resonant transition. Polarization effects arise when the polarization vector is set parallel to t he c crystallographic axis or perpendicular to it (I c and I ab respectively). The LD is the difference between the two spectra (I ab -I c ) and gives a direct insight of the empty Mn 3dstates: a LD which is on average positive (negative) indicates a majority o f off-plane (in-plane) empty 3d states. Considering the crystal field splitting, the effect can be mainly related to the occupation of the two e g states (3r 2 -z 2 and x 2 -y 2 ) with majority spin: a LD which is on average positive (negative) is due to a preferential occupation of the in-plane x 2 -y 2 (out-of-plane 3r 2 -z 2 )orbital.Magnetization measurements were carried out by a SQUID magnetometer. Further experimental details are given in ref.[16] and [26].In Fig.2 Fig.4(b), revealing opposite signs for these two cases.Although the comparison with experiments can only be qualitative and a proper fit is not feasible, the sign reversal is observed in the experimental spectra of Fig.4(a) for energies above the E˜644 ...

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Because of a typing error, the paragraph starting on page 2, line 43 should read: ''The LD is the difference between the two spectra (I ab =I c ) and gives a direct insight of the empty Mn 3d states: a LD which is on average negative (positive) indicates a majority of off-plane (in-plane) empty 3d states. Considering the crystal field splitting, the effect can be mainly related to the occupation of the two e g states (3r 2 À z 2 and x 2 À y 2 ) with majority spin: a LD which is on average negative (positive) is due to a preferential occupation of the in-plane x 2 À y 2 (out-of-plane 3r 2 À z 2 ) orbital. '' PRL 103, 079902 (2009)

Recent developments in the fi eld of thin-fi lm growth technologies have allowed control at an atomic level of deposited layers, thus opening new perspectives in the fi eld of engineering of multilayers and heterostructures based on complex oxides. [ 1 ] In particular, it is expected that oxide heterostructures, with almost ideal interfaces, may lead to interesting artifi cial materials with novel properties. Artifi cial thin-fi lm oxide structures make the already complex individual bulk properties even more interesting through their interaction at the interface. Following such an approach, a number of heterostructures have been tailored which show extraordinary properties that do not belong to the individual layers. These range from superconductivity at the interface between nonsuperconducting layers to high-mobility 2D conductivity at the interface between insulating oxides. [ 2 , 3 ] The number of possible combinations of these oxides is enormous, and the potential for novel behavior having practical applications represents a strong motivation for this research.The same approach can be applied to heterostructures based on oxide ionic conductors provided that the issues concerning structural match at the interface are solved. The interest in heterostructures based on oxide ionic conductors is driven by the space-charge-zone effects at the interface, which can increase the charge-carrier concentration locally, and by interface mobility effects, the latter being of particular relevance in the case of materials with high defect density and relatively low mobility. The potential impact of oxide ionic conductor superlattices has been shown for superlattices based on CaF 2 and BaF 2 layers, grown by molecular beam epitaxy, which exhibited an increase in ionic conductivity