Unveiling the outstanding oxygen mass transport properties of Mn-rich perovskites in grain boundary-dominated La0.8Sr0.2(Mn1-xCox)0.85O3-d nanostructures

Ion transport in solid-state devices is of great interest for current and future energy and information technologies. A superior enhancement of several orders of magnitude of the oxygen diffusivity has been recently reported for grain boundaries in lanthanum strontium manganites. However, the significance and extent of this unique phenomenon is not yet established. Here, we fabricate a thin film continuous composition map of the La0.8Sr0.2(Mn1-xCox)0.85O3-d family revealing a substantial enhancement of the grain boundary oxygen mass transport properties for the entire range of compositions. Through isotope-exchange depth profiling coupled to secondary ion mass spectroscopy, we show that this excellent performance is not directly linked to the bulk of the material but to the intrinsic nature of the grain boundary. In particular, the great increase of the oxygen diffusion in Mn-rich compositions unveils an unprecedented catalytic performance in the field of Mixed Ionic Electronic Conductors. These results present grain boundaries engineering as a novel strategy for designing highly performing materials for solid state ionics based devices

The impact of Mn nonstoichiometry on the oxygen mass transport properties of La0.8Sr0.2MnyO3±δ thin films

Oxygen mass transport in perovskite oxides is relevant for a variety of energy and information technologies. In oxide thin films, cation nonstoichiometry is often found but its impact on the oxygen transport properties is not well understood. Here, we used oxygen isotope exchange depth profile technique coupled with secondary ion mass spectrometry to study oxygen mass transport and the defect compensation mechanism of Mn-deficient La0.8Sr0.2Mn (y) O-3 +/-delta epitaxial thin films. Oxygen diffusivity and surface exchange coefficients were observed to be consistent with literature measurements and to be independent on the degree of Mn deficiency in the layers. Defect chemistry modeling, together with a collection of different experimental techniques, suggests that the Mn-deficiency is mainly compensated by the formation of La-x(Mn) antisite defects. The results highlight the importance of antisite defects in perovskite thin films for mitigating cationic nonstoichiometry effects on oxygen mass transport properties

<i>Operando </i>Electron Microscopy and Impedance Analysis of Solid Oxide Electrolysis and Fuel Cells

Operando transmission electron microscopy (TEM) integrated with electrochemical impedance spectroscopy (EIS) is applied to the analysis of a model solid oxide electrolysis/fuel cell (SOEC/SOFC). The cell features electrodes made of gadolinia-doped ceria (CGO) and an electrolyte of yttria-stabilized zirconia (YSZ). Fabricated through pulsed laser deposition (PLD) and subsequent FIB-SEM processing procedures, the model cells were mounted on MEMS chips for operando TEM. Testing was carried out in an environmental TEM (ETEM) under reactive gases (H2 and H2O) at elevated temperatures relevant for SOEC and SOFC operation and under applied electrical potential. The activation energies for the YSZ ionic transport and CGO surface reaction were found to be 0.9 and 0.5 eV, respectively, aligning with literature values. The work demonstrates the feasibility of conducting SOEC/SOFC full cell tests directly within the ETEM, including EIS analysis during cell operation, offering deep insight into the cell contributions: electrochemical reactions, transport, and degradation mechanisms.</p

The impact of Mn nonstoichiometry on the oxygen mass transport properties of La0.8Sr0.2Mn y O3±δ thin films

Oxygen mass transport in perovskite oxides is relevant for a variety of energy and information technologies. In oxide thin films, cation nonstoichiometry is often found but its impact on the oxygen transport properties is not well understood. Here, we used oxygen isotope exchange depth profile technique coupled with secondary ion mass spectrometry to study oxygen mass transport and the defect compensation mechanism of Mn-deficient LaSrMn O epitaxial thin films. Oxygen diffusivity and surface exchange coefficients were observed to be consistent with literature measurements and to be independent on the degree of Mn deficiency in the layers. Defect chemistry modeling, together with a collection of different experimental techniques, suggests that the Mn-deficiency is mainly compensated by the formation of La Mn × antisite defects. The results highlight the importance of antisite defects in perovskite thin films for mitigating cationic nonstoichiometry effects on oxygen mass transport properties.This research was supported by the funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement No. 101017709 (EPISTORE) and the 'Generalitat de Catalunya' (2017 SGR 1421, NANOEN). LY acknowledges support from the MINECO (Spain) through the IJC2018-037698-I grant. MICIIN projects PID2019-106165GB-C21 and RED2018-102609-T are also acknowledged. PN acknowledges the support from the AGAUR through the 2021 FI_B 00157 Grant. RADS acknowledges funding from German Research Foundation (DFG) from project DE 2854/12-1 and from the collaborative research center SFB917 'Nanoswitches'. J S acknowledges the financial support of the Spanish Ministry of Economy, Industry and Competitiveness (Project: PID2019-108573GB-C21)

Reconstruction of Low Dimensional Electronic States by Altering the Chemical Arrangement at the SrTiO₃ Surface

Developing reliable methods for modulating the electronic structure of the 2D electron gas (2DEG) in SrTiO3 is crucial for utilizing its full potential and inducing novel properties. Herein, it is shown that relatively simple surface preparation reconstructs the 2DEG at the SrTiO3 (STO) surface, leading to a Lifshitz-like transition. Combining experimental methods, such as angle-resolved photoemission spectroscopy (ARPES) and X-ray photoemission spectroscopy with ab initio calculations, that the modulation of the surface band structures can be effectively achieved via transforming the chemical composition at the atomic scale is found. In addition, ARPES experiments demonstrate that vacuum ultraviolet light can be efficiently employed to alter the band renormalization of the 2DEG system and control the electron-phonon interaction . This study provides a robust and straightforward route to stabilize and tune the low-dimensional electronic structure via the chemical degeneracy of the STO surface

Disclosing the response of the surface electronic structure in SrTiO₃ (001) to strain

Combining angle-resolved photoemission spectroscopy and density functional theory calculations, we addressed the surface electronic structure of bent SrTiO 3 (STO) (001) wafers. Using a custom-made device, we observe that the low-dimensional states that emerge at the STO (001) surface are robust to an external tensile strain of about 0.1%. Our results show that this value of strain is too small to sensibly alter the surface conduction band of STO, but, surprisingly, it is enough to shift the energy of the in-gap states. In order to access higher strain values of around 2%, standard for STO-based heterostructures, we performed density functional theory calculations of STO slabs under different strain configurations. The simulations predict that such levels of both compressive and tensile strain significantly alter the orbital splitting of the surface conduction band. Our study indicates that the strain generated in STO can tailor the electronic properties of its bare surface and of STO-based interfaces