Oxygen Migration Pathways in Layered LnBaCo2O6-δ (Ln = La - Y) Perovskites

Layered LnBaCo2O6-δ perovskites are important mixed ionic-electronic conductors, exhibiting outstanding catalytic properties for the oxygen evolution/reduction reaction. These phases exhibit considerable structural complexity, in particular, near room temperature, where a number of oxygen vacancy ordered superstructures are found. This study uses bond valence site energy calculations to demonstrate the key underlying structural features that favor facile ionic migration. BVSE calculations show that the 1D vacancy ordering for Ln = Sm-Tb could be beneficial at low temperatures as new pathways with reduced barriers emerge. By contrast, the 2D vacancy ordering for Ln = Dy and Y is not beneficial for ionic transport with the basic layered parent material having lower migration barriers. Overall, the key criterion for low migration barriers is an expanded ab plane, supported by Ba, coupled to a small Ln size. Hence, Ln = Y should be the best composition, but this is stymied by the low temperature 2D vacancy ordering and moderate temperature stability. The evolution of the oxygen cycling capability of these materials is also reported.

Stability and Evolution of the Crystal Structure of TbBaCo2O6-δ During Thermal Oxygen Release/Uptake

A-site ordered double perovskites with the general formula LnBaCo₂O_6-δ (where Ln is a lanthanide element) present electrical and electrocatalytic properties that make them attractive as possible ceramic electrode materials for solid oxide cells or alkaline electrolyzers. The properties are highly influenced by the anion vacancy concentration, which is strongly related to the Co-oxidation state, and their location in the structure. Awareness of the stable phases is essential to synthesize, evaluate, and optimize the properties of LnBaCo₂O_6-δ oxides at operating conditions in different applications. TbBaCo₂O_6-δ are representative oxides of these layered perovskite systems. The present article reports a study of TbBaCo₂O_6-δ by electron diffraction, high-resolution electron microscopy, and powder neutron diffraction experiments at different temperatures. The synthesis of TbBaCo₂O_6-δ in air and slow cooling to room temperature (RT) at 5 °C h^-1 leads to samples formed by distinct phases with different oxygen contents and crystal structures. The 122 and 112 phases (with a_p × 2a_p × 2a_p and a_p × a_p × 2a_p unit cells, respectively, with a_p being the lattice parameter of the simple cubic perovskite structure) are predominant in quasi-equilibrium prepared samples (cooled at RT at 1 °C h^-1) or prepared in Ar flow and quenched to RT. The evolution of the crystal structure of TbBaCo₂O_6-δ during thermal oxygen release/uptaking consists of modulation from the 122 phase to the 112 phase (or vice versa during uptaking) by creation/occupation of anion vacancies within the TbO_1-δ planes. Anion vacancies are not detected in the oxygen crystallographic position different from those located within the TbO_1-δ planes even at the highest temperatures, supporting the 2D character of the high anion conduction of the LnBaCo₂O_6-δ oxides.

Effect of Infiltration Ce0.8Sm0.2O1.9 Against Double Perovskite Performance LaBa0.5Sr0.5Co2O5+δ as IT-SOFC Cathode

Modifying the sample surface by infiltration technique using Ce0.8Sm0.2O1.9 (SDC) electrolyte has been done to increase the catalytic activity of the LaBa0.5Sr0.5Co2O5+δ (LBSC) cathode. The cathode powder structure was evaluated using X-ray diffraction (XRD) at room temperature, and the LBSC cathode microstructure was analyzed using scanning electron microscopy (SEM). The electrical conductivity of the LBSC cathode was tested using the four-probe DC method. Symmetrical cells were tested using a potentiostat Voltalab PGZ 301 and a digital source meter Keithley 2420. LBSC powder was discovered to have a tetragonal structure (space group: P4/mmm) with lattice parameters of a = 3.86253 Å, c = 7.73438 Å, and V = 115.338 Å. From the SEM image, the LBSC cathode has homogeneous, dense, and highly porous grains. The electrical conductivity showed metallic behavior, gradually decreasing from 167 S.cm-1 at 300℃ to 105 S.cm-1 at 800℃. A significant increase in current density (io) of 275% occurred at 800℃ from 154.10 mA.cm−2 (pure LBSC) to 577.86 mA.cm−2 (LBSC+0.5M SDC). The activation energy value (Ea) of symmetrical cells was determined using electrochemical impedance spectroscopy (EIS), low-field (LF), and high-field (HF) techniques. The activation energy of the LBSC+0.5 M SDC specimen was 47.9 kJ mol-1 or 79.4% lower than the activation energy of the LBSC cathode specimen without infiltration at atmospheric pressure of 0.03 atm. These results indicate that SDC infiltration of the LBSC cathode can reduce the activation energy of the significant. The cathode membrane adheres quite well to the electrolyte membrane, the cathode porosity varies in the range of 1–4 µm, and the grain size is 0.1–1.5 µm.

Nonstoichiometry, Defect Chemistry and Oxygen Transport in Fe-Doped Layered Double Perovskite Cobaltite PrBaCo2-xFexO6-δ (x = 0-0.6) Membrane Materials

Mixed conducting cobaltites PrBaCo_2-xFe_xO_6-δ (x = 0-0.6) with a double perovskite structure are promising materials for ceramic semi-permeable membranes for oxygen separation and purification due to their fast oxygen exchange and diffusion capability. Here, we report the results of the detailed study of an interplay between the defect chemistry, oxygen nonstoichiometry and oxygen transport in these materials as a function of iron doping. We show that doping leads to a systematic variation of both the thermodynamics of defect formation reactions and oxygen transport properties. Thus, iron doping can be used to optimize the performance of mixed conducting oxygen-permeable double perovskite membrane materials.

Triple Perovskite Nd1.5Ba1.5CoFeMnO9−δ-Sm0.2Ce0.8O1.9 Composite as Cathodes for the Intermediate Temperature Solid Oxide Fuel Cells

Triple perovskite has been recently developed for the intermediate temperature solid oxide fuel cell (IT-SOFC). The performance of Nd1.5Ba1.5CoFeMnO9−δ (NBCFM) cathodes for IT-SOFC is investigated in this work. The interfacial polarization resistance (RP) of NBCFM is 1.1273 Ω cm2~0.1587 Ω cm2 in the range of 700–800 °C, showing good electrochemical performance. The linear thermal expansion coefficient of NBCFM is 17.40 × 10−6 K−1 at 40–800 °C, which is significantly higher than that of the electrolyte. In order to further improve the electrochemical performance and reduce the thermal expansion coefficient (TEC) of NBCFM, Ce0.8Sm0.2O2−δ (SDC) is mixed with NBCFM to prepare an NBCFM-xSDC composite cathode (x = 0, 10, 20, 30, 40 wt.%). The thermal expansion coefficient decreases monotonically from 17.40 × 10−6 K−1 to 15.25 × 10−6 K−1. The surface oxygen exchange coefficient of NBCFM-xSDC at a given temperature increases from 10−4 to 10−3 cm s−1 over the po2 range from 0.01 to 0.09 atm, exhibiting fast surface exchange kinetics. The area specific resistance (ASR) of NBCFM-30%SDC is 0.06575 Ω cm2 at 800 °C, which is only 41% of the ASR value of NBCFM (0.15872 Ω cm2). The outstanding performance indicates the feasibility of NBCFM-30% SDC as an IT-SOFC cathode material. This study provides a promising strategy for designing high-performance composite cathodes for SOFCs based on triple perovskite structures.

Insights into Oxygen Migration in LaBaCo2O6-δ Perovskites from In Situ Neutron Powder Diffraction and Bond Valence Site Energy Calculations

Layered cobalt oxide perovskites are important mixed ionic and electronic conductors. Here, we investigate LaBaCo₂O_6-δ using in situ neutron powder diffraction. This composition is unique because it can be prepared in cubic, layered, and vacancy-ordered forms. Thermogravimetric analysis and diffraction reveal that layered and disordered samples have near-identical oxygen cycling capacities. Migration barriers for oxide ion conduction calculated using the bond valence site energy approach vary from E _b ∼ 2.8 eV for the cubic perovskite to E _b ∼ 1.5 eV for 2D transport in the layered system. Vacancy-ordered superstructures were observed at low temperatures, 350-400 °C for δ = 0.25 and δ = 0.5. The vacancy ordering at δ = 0.5 is different from the widely reported structure and involves oxygen sites in both CoO₂ and LaO planes. Vacancy ordering leads to the emergence of additional migration pathways with low-energy barriers, for example, 1D channels with E _b = 0.5 eV and 3D channels with E _b = 2.2 eV. The emergence of these channels is caused by the strong orthorhombic distortion of the crystal structure. These results demonstrate that there is potential scope to manipulate ionic transport in vacancy-ordered LnBaCo₂O_6-δ perovskites with reduced symmetry.

Dual nature of high-temperature electronic transport in layered perovskite-like cobaltites: exhaustive consideration of experimental features observed

Complex oxides with the general formula Pr_1-xY_xBaCo_2-yNi_yO_6-δ (x = 0, 0.1, y = 0, 0.2) were successfully synthesized via combustion of organo-metallic precursors. The high-temperature dc conductivity of the obtained sintered materials was studied in a wide range of oxygen partial pressures and temperatures by means of the 4-probe method. The resulting dependencies were juxtaposed with the previously published data on oxygen non-stoichiometry for the oxides considered. The comprehensive analysis of these datasets in attempts to explain the observed trends has shown the large inadequacy of currently existing conduction models. Consequently, a new model approach was developed to account for the numerous experimental and theoretical peculiarities being characteristic for the cobaltites with a layered double perovskite structure. One of the key propositions made postulates mixed nature of the band structure for materials studied with spin states of Co ions acting as a spatial descriptor of a particular type of conductivity: semiconducting or a metallic one. The abovementioned hypothesis was validated by magnetic, thermodynamic and structural arguments obtained both theoretically and experimentally. The models suggested were shown to be adequate in describing large arrays of data collected. Additionally, the reasons behind doping and temperature/pressure influences on the respective conductivity changes in Pr_1-xY_xBaCo_2-yNi_yO_6-δ were uncovered. Transport and thermodynamic parameters determined were used to evaluate transference numbers and mobilities of different charge carriers which revealed the dominating role of metallic conductivity under oxidative conditions and the superiority of semiconducting charge transport in reducing environments. The obtained conclusions were further supported by utilizing the derived model equations for successful description of conductivity/non-stoichiometry data for other layered cobaltites. Also, interesting correlations between cation composition, thermodynamic and transport properties were found. Finally, general review of the formulated approach was made and further research directions were proposed.

Progress and prospects of reversible solid oxide fuel cell materials

Reversible solid oxide fuel cell (RSOFC) is an energy device that flexibly interchanges between electrical and chemical energy according to people's life and production needs. The development of cell materials affects the stability and cost of the cell, but also restricts its market-oriented development. After decades of research by scientists, a lot of achievements and progress have been made on RSOFC materials. According to the composition and requirements of each component of RSOFC, this article summarizes the research progress based on materials and discusses the merits and demerits of current cell materials in electrochemical performance. According to the efficiency of different materials in solid oxide fuel cell (SOFC mode) and solid oxide electrolyzer (SOEC mode), the challenges encountered by RSOFC in the operation are evaluated, and the future development of RSOFC materials is boldly prospected.

Theoretical Investigation of Proton Diffusion in Dion-Jacobson Layered Perovskite RbBiNb2O7

Perovskite materials are considered to be promising electrolyte membrane candidates for electrochemical applications owing to their excellent proton- or oxide-ion-conducting properties. RbBiNb₂O₇ is a double-layered Dion–Jacobson perovskite oxide, with Pmc2₁ symmetry. In this study, the electronic structure and proton-diffusion properties of bulk RbBiNb₂O₇ were systematically investigated using first-principles calculations. The unique layered crystal structure of RbBiNb₂O₇ plays a crucial role in proton storage and proton conductivity. Different proton-diffusion steps in RbBiNb₂O₇ were considered, and the activation energies of the relevant diffusion steps were evaluated using the climbing image-nudged elastic band (CI-NEB) technique. The proton diffusion in RbBiNb₂O₇ presents a two-dimensional layered characteristic in the a-b plane, owing to its layered crystalline nature. According to the transition state calculations, our results show that the bulk RbBiNb₂O₇ exhibits good proton-transport behavior in the a-b plane, which is better than many perovskite oxides, such as CaTiO₃, CaZrO₃, and SrZrO₃. The proton diffusion in the Rb–O and Nb–O layers is isolated by a higher energy barrier of 0.86 eV. The strong octahedral tilting in RbBiNb₂O₇ would promote proton transport. Our study reveals the microscopic mechanisms of proton conductivity in Dion–Jacobson structured RbBiNb₂O₇, and provides theoretical evidence for its potential application as an electrolyte in solid oxide fuel cells (SOFCs).

Triple ionic-electronic conducting oxides for next-generation electrochemical devices

Triple ionic-electronic conductors (TIECs) are materials that can simultaneously transport electronic species alongside two ionic species. The recent emergence of TIECs provides intriguing opportunities to maximize performance in a variety of electrochemical devices, including fuel cells, membrane reactors and electrolysis cells. However, the potential application of these nascent materials is limited by lack of fundamental knowledge of their transport properties and electrocatalytic activity. The goal of this Review is to summarize and analyse the current understanding of TIEC transport and electrochemistry in single-phase materials, including defect formation and conduction mechanisms. We particularly focus on the discovery criteria (for example, crystal structure and ion electronegativity), design principles (for example, cation and anion substitution chemistry) and operating conditions (for example, atmosphere) of materials that enable deliberate tuning of the conductivity of each charge carrier. Lastly, we identify important areas for further advances, including higher chemical stability, lower operating temperatures and discovery of n-type TIEC materials.

Structural Ordering Supremacy on the Oxygen Reduction Reaction of Layered Iron-Perovskites

Layered perovskites of the Gd_0.8-xBa_0.8Ca_0.4+xFe₂O_5+δ system show oxygen reduction reaction (ORR) activity. The layered crystal structure of these oxides is established by the interplay of the Gd³⁺, Ba²⁺, and Ca²⁺ locations with the ordering of the coordination polyhedra of the Fe³⁺ cations. Substitution of Gd³⁺ by Ca²⁺ increases the oxygen deficiency that is accommodated by the formation of layers of FeO₅-squared pyramids intercalated with A-O layers containing mainly Gd³⁺. The presence of FeO₅-squared pyramids in the crystal structure promotes the oxygen diffusion and then the ORR activity. Therefore, GdBa₂Ca₂Fe₅O₁₃ is the oxide of the system which presents lower area specific resistance (ASR) values when it is applied as an electrode in symmetrical cells using Ce_0.9Gd_0.1O_2-δ as an electrolyte.

Self-Diffusion in Perovskite and Perovskite Related Oxides: Insights from Modelling

Perovskite and perovskite related oxides are important materials with applications ranging from solid oxide fuel cells, electronics, batteries and high temperature superconductors. The investigation of physical properties at the atomic scale such as self-diffusion is important to further improve and/or miniaturize electronic or energy related devices. In the present review we examine the oxygen self-diffusion and defect processes in perovskite and perovskite related oxides. This contribution is not meant to be an exhaustive review of the literature but rather aims to highlight the important mechanisms and ways to tune self-diffusion in this important class of energy materials.

Successive and Site-Selective Oxygen Release from B-Site-Layer-Ordered Double Perovskite Ca2FeMnO6 with Unusually High Valence Fe4

B-site-layer-ordered double perovskite Ca₂FeMnO₆ with unusually high valence Fe⁴⁺ was found to exhibit unusual oxygen-release behaviors, contrasting with those of the B-site-disordered perovskite having the identical chemical composition. During heating, the B-site-layer-ordered compound shows a stepwise oxygen release with successive valence changes from Fe⁴⁺ to Fe³⁺ through an intermediate Fe^3.5+, whereas the B-site-disordered compound releases oxygen in a single step. The oxygen in Ca₂FeMnO₆ is released only from the two-dimensional Fe layers, and this selective oxygen release stabilizes the intermediate Fe^3.5+ phase with in-plane-oxygen-vacancy ordering. Therefore, the B-site order/disorder strongly affects the oxygen-release behaviors associated with the oxygen-vacancy ordering.

Rate-Determining Steps of Oxygen Surface Exchange Kinetics on Sr2Fe1.5Mo0.5O6−δ

The oxygen surface kinetics of Sr2Fe1.5Mo0.5O6−δ was determined using the 16O2/18O2 isotope exchange method with gas phase analysis at 600–800 °C. The heterogeneous exchange rates (rH) and the oxygen diffusion coefficients (D) were calculated by processing the concentration dependences of the 18O fraction using Ezin’s model. The rates of oxygen dissociative adsorption (ra) and incorporation (ri) were calculated based on a model using the three exchange type rates. It has been established that the rates ra and ri were comparable in this temperature range. Assumptions were made about the effect of the chemical composition of the surface on the rate of oxygen adsorption. It was found that the oxygen exchange coefficient (k) of Sr2Fe1.5Mo0.5O6−δ is comparable to that of La0.6Sr0.4MnO3±δ oxide. High values of the oxygen diffusion coefficient were found for Sr2Fe1.5Mo0.5O6−δ. The values were comparable to those of the double cobaltite praseodymium-barium and exceed by more than an order those of lanthanum-strontium manganite.

Identification of oxygen diffusion mechanisms in Nd1-xAExBaInO4-x/2 (AE = Ca, Sr, Ba) compounds through molecular dynamics

Molecular dynamics simulations have been widely adopted to study oxygen ion diffusion mechanisms in materials for application in solid oxide fuel cells. Indeed, understanding the fundamental aspects of oxygen diffusion is important to develop new materials for this application. In this work, Nd1-xAExBaInO4-x/2 (AE = Ca, Sr, Ba) compounds have been studied by MD simulations focusing on oxygen diffusion mechanisms. Two general clustering methods were used, namely a convex hull classification method and a DBSCAN machine learning algorithm, to identify oxygen ion diffusion pathways. Here, relevant details are provided for an efficient use of these two approaches during MD analysis of ion conductors. The calculations show that Ca is the most favorable dopant for substituting Nd in NdBaInO4, while Ba is the least desired. Indeed, the substitution of Nd by Ca hardly changes the pristine lattice parameters of NdBaInO4 and leads to the highest oxygen diffusion coefficient compared to other dopants. The oxygen vacancies induced by doping mainly locate on two specific oxygen sites over four oxygen sites available. Concerning the diffusion process, jumps involving these two sites play the main role and are associated with smaller migration enthalpies. For the main diffusion path, ions migrate along the b (2 routes) and c (4 routes) directions. Some other oxygen sites can be considered as barriers for the diffusion process inducing a strong anisotropy in the diffusion process. Additionally, the residence time analysis of oxygen ions confirms that ions at different sites have different motion abilities. As a whole, the approach presented here can be extrapolated to other ion conductors for gaining detailed information about the diffusion process.

Defect Chemistry and Li-ion Diffusion in Li2RuO3

Layered Li₂RuO₃ is an important candidate cathode material in rechargeable lithium ion batteries because of its novel anionic redox process and high reversible capacity. Atomistic scale simulations are used to calculate the intrinsic defect process, favourable dopants and migration energies of lithium ion diffusions together with migration paths in Li₂RuO₃. The Li Frenkel is calculated to be the most favourable intrinsic defect type. The cation anti-site defect, in which Li and Ru ions exchange their positions is 1.89 eV/defect suggesting that this defect would be observed at high temperatures. Long range vacancy assisted lithium diffusion paths were calculated and it is confirmed that the lowest overall activation energy (0.73 eV) migration path is along the ab plane. Trivalent dopants (Al³⁺, Co³⁺, Sc³⁺, In³⁺, Y³⁺, Gd³⁺ and La³⁺) were considered to create additional Li in Li₂RuO₃. Here we show that Al³⁺ or Co³⁺ are the ideal dopants and this is in agreement with the experimental studies reported on Co³⁺ doping in Li₂RuO₃.

Defects and dopant properties of Li3V2(PO4)3

Polyanion phosphate based Li₃V₂(PO₄)₃ material has attracted considerable attention as a novel cathode material for potential use in rechargeable lithium ion batteries. The defect chemistry and dopant properties of this material are studied using well-established atomistic scale simulation techniques. The most favourable intrinsic defect process is the Li Frenkel (0.45 eV/defect) ensuring the formation of Li vacancies required for Li diffusion via the vacancy mechanism. Long range lithium paths via the vacancy mechanism were constructed and it is confirmed that the lowest activation energy of migration (0.60 eV) path is three dimensional with curved trajectory. The second most stable defect energy process is calculated to be the anti-site defect, in which Li and V ions exchange their positions (0.91 eV/defect). Tetravalent dopants were considered on both V and P sites in order to form Li vacancies needed for Li diffusion and the Li interstitials to increase the capacity respectively. Doping by Zr on the V site and Si on the P site are calculated to be energetically favourable.

A review of high temperature co-electrolysis of H2O and CO2 to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO₂ emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO₂ electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult C[double bond, length as m-dash]O double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO₂ conversion and utilization. Here, we discuss in detail the approaches of CO₂ conversion, the developmental history, the basic principles, the economic feasibility of CO₂/H₂O co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO₂ electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.

Evidence for percolation diffusion of cations and reordering in disordered pyrochlore from accelerated molecular dynamics

Diffusion in complex oxides is critical to ionic transport, radiation damage evolution, sintering, and aging. In complex oxides such as pyrochlores, anionic diffusion is dramatically affected by cation disorder. However, little is known about how disorder influences cation transport. Here, we report results from classical and accelerated molecular dynamics simulations of vacancy-mediated cation diffusion in Gd₂Ti₂O₇ pyrochlore, on the microsecond timescale. We find that diffusion is slow at low levels of disorder, while higher disorder allows for fast diffusion, which is then accompanied by antisite annihilation and reordering, and thus a slowing of cation transport. Cation diffusivity is therefore not constant, but decreases as the material reorders. We also show that fast cation diffusion is triggered by the formation of a percolation network of antisites. This is in contrast with observations from other complex oxides and disordered media models, suggesting a fundamentally different relation between disorder and mass transport.Diffusion plays an important role in sintering, damage tolerance and transport. Here authors perform classical and accelerated molecular dynamics simulations of vacancy-mediated cation diffusion in Gd₂Ti₂O₇ pyrochlore and report non-monotonic evolution of cation diffusivity.

O vacancy formation in (Pr/Gd)BaCo2O5.5 and the role of antisite defects

In search for materials for intermediate temperature solid oxide fuel cells, (Pr/Gd)BaCo₂O_5.5 is investigated by first principles calculations. Antisite defects are considered as they may modify the electronic and O diffusion properties but are rarely studied in double perovskite oxides. Octahedrally coordinated Co atoms are shown to realize intermediate and high spin states for PrBaCo₂O_5.5 and GdBaCo₂O_5.5, respectively, while pyramidally coordinated Co atoms always have high spin. It turns out that O vacancy formation is significantly easier in PrBaCo₂O_5.5 than in GdBaCo₂O_5.5, the difference in formation energy being hardly modified by antisite defects. While pyramidally coordinated Co atoms are not affected, we show that the presence of antisite defects causes parts of the octahedrally coordinated Co atoms to switch from intermediate to high spin.

Crystal Structures at Atomic Resolution of the Perovskite-Related GdBaMnFeO5 and Its Oxidized GdBaMnFeO6

Perovskite-related GdBaMnFeO₅ and the corresponding oxidized phase GdBaMnFeO₆, with long-range layered-type ordering of the Ba and Gd atoms have been synthesized. Oxidation retains the cation ordering but drives a modulation of the crystal structure associated with the incorporation of the oxygen atoms between the Gd layers. Oxidation of GdBaMnFeO₅ increases the oxidation state of Mn from 2+ to 4+, while the oxidation state of Fe remains 3+. Determination of the crystal structure of both GdBaMnFeO₅ and GdBaMnFeO₆ is carried out at atomic resolution by means of a combination of advanced transmission electron microscopy techniques. Crystal structure refinements from synchrotron X-ray diffraction data support the structural models proposed from the TEM data. The oxidation states of the Mn and Fe atoms are evaluated by means of EELS and Mössbauer spectroscopy, which also reveals the different magnetic behavior of these oxides.

Evaluation of Ba-deficient PrBa1−xFe2O5+δ oxides as cathode materials for intermediate-temperature solid oxide fuel cells

Cobalt-free double perovskite oxides are promising cathode materials in intermediate-temperature solid oxide fuel cells, and often suffer from low activity in oxygen reduction reactions.

Relating surface chemistry and oxygen surface exchange in LnBaCo2O5+δ air electrodes

The surface and near-surface chemical composition of electroceramic materials often shows significant deviations from that of the bulk. In particular, layered materials, such as cation-ordered LnBaCo₂O_5+δ perovskites (Ln = lanthanide), undergo surface and sub-surface restructuring due to the segregation of the divalent alkaline-earth cation. These processes can take place during synthesis and processing steps (e.g. deposition, sintering or annealing), as well as at temperatures relevant for the operation of these materials as air electrodes in solid oxide fuel cells and electrolysers. Furthermore, the surface segregation in these double perovskites shows fast kinetics, starting at temperatures as low as 400 °C over short periods of time and leading to a decrease in the transition metal surface coverage exposed to the gas phase. In this work, we use a combination of stable isotope tracer labeling and surface-sensitive ion beam techniques to study the oxygen transport properties and their relationship with the surface chemistry in ordered LnBaCo₂O_5+δ perovskites. Time-of-Flight Secondary-Ion Mass Spectrometry (ToF-SIMS) combined with ¹⁸O isotope exchange was used to determine the oxygen tracer diffusion (D*) and surface exchange (k*) coefficients. Furthermore, Low Energy Ion Scattering (LEIS) was used for the analysis of the surface and near surface chemistry as it provides information from the first mono-atomic layer of the materials. In this way, we could relate the compositional modifications (e.g. cation segregation) taking place at the electrochemically-active surface during the exchange at high temperatures and the oxygen transport properties in double perovskite electrode materials to further our understanding of the mechanism of the surface exchange process.

A molecular dynamics study of oxygen ion diffusion in A-site ordered perovskite PrBaCo2O5.5: data mining the oxygen trajectories

Data mining the trajectories of molecular dynamics simulations leads to a better understanding of oxygen diffusion in perovskites.

Ordering effects in the crystal structure and electrochemical properties of the Gd0.5Ba0.5Mn0.5Fe0.5O3−δ perovskite

Layered-type ordering of Ba and Gd atoms in BaGdMnFeO_6−δ perovskite studied by HAADF-STEM and EELS mapping.

Accelerated materials design of Na0.5Bi0.5TiO3 oxygen ionic conductors based on first principles calculations

First principle calculations are performed to accelerate the design of new oxygen ionic conductors.

Oxygen nonstoichiometry, defect structure and oxygen diffusion in the double perovskite GdBaCo2O6−δ

The values of the oxygen self-diffusion coefficient measured by the dc-polarization technique completely coincide with those of the oxygen tracer diffusion coefficient.