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The theoretical analysis of oxygen-ion conductivity in double perovskite type oxides was performed. The model of ion transport was developed by considering two energetically non-equivalent oxygen positions for ion jumps in the crystalline structure. The temperature variations of oxygen ion conductivity were shown to depend on thermodynamic parameters of the intrinsic oxygen disordering process. The model proposed was verified by experimental data for perovskite-like non-stoichiometric PrBaCo2O6–δ, Sr3Fe2O7–δ and its titanium-doped derivative.

The novel Cl−-doped compound based on oxygen deficient double perovskite Ba2CaNbO5.5 was synthesized Ba2CaNbO5.48Cl0.05 and its structure, thermal properties, hydration behavior and electrical properties have been investigated. It was found that introduction of Cl− ions leads to the increasing of oxygen ion and proton conductivities. The appearance of donor defect Clo (or Fo ) decreases the activation energy for oxygen ion transport and increases the mobility of oxygen vacancies due to electrostatic repulsion between the positive charged defects Vo and Clo (Fo ). It was shown that Cl−-doping decreases proton concentration but enhances proton conductivity due to significant increase in proton mobility.

Oxide interfaces have attracted a huge amount of interest in recent years due to their novel functionalities that are not possible in bulk. Here we employ atomistic simulation techniques to study the defect properties and oxygen ion migration energy in bulk SrTiO3, LaCrO3 and SrTiO3–LaCrO3 interface. The SrO and La2O3 “Schottky-like” defects are found to be the most favourable intrinsic defects in their respective bulk structures and also at interface layers. While defect energies calculated at interface layers are not significantly changed compared to that calculated in the bulk LaCrO3, significant changes are noted in Schottky defects and oxygen Frenkel between bulk SrTiO3 and the interface. The activation energies for the oxygen ion diffusion in bulk SrTiO3 and LaCrO3 are calculated to be 0.64 eV and 0.53 eV, respectively, suggesting that both materials will present favourable diffusion pathways. In general, there is a reduction in the activation energies of oxygen ion migration at the interface compared to bulk structures. In particular, in the Cr layer, activation energy is calculated to be 0.36 eV implying that interface plays an important role in the oxygen ion migration and therefore such an interface is of interest for use in advanced electrochemical devices.

Perovskites with fast oxygen ion conduction can enable technologies like solid oxide fuel cells. One component of fast oxygen ion conduction is low oxygen migration barrier. Here we apply ab initio methods on over 40 perovskites to produce a database of oxygen migration barriers ranging from 0.2 to 1.6 eV. Mining the database revealed that systems with low barriers also have low metal-oxygen bond strength, as measured by oxygen vacancy formation energy and oxygen p-band center energy. These correlations provide a powerful descriptor for the development of new oxygen ion conductors and may explain the poor stability of some of the best oxygen conducting perovskites under reducing conditions. Other commonly-cited measures of space, volume, or structure ideality showed only weak correlation with migration barrier. The lowest migration barriers (< 0.5 eV) belong to perovskites with non-transition-metal B-site cations, and may require vacancy-creation strategies that involve no dopants or low-association dopants for optimal performance., Final draft and SI in single PDF

The temperature dependence of oxygen ion behavior in Zn 2 GeO 4 has been studied from 78 to 873 K. As the temperature increases, the oxygen ions undergo positional disordering along the oxygen vacancies, with the oxygen related modes (ORMs) at 751 cm − 1 and 775 cm − 1 broadening and weakening dramatically. The temperature dependence of the bandwidth of oxygen ion mode is particularly interesting and a model suggested by Andrade and Porto is used to describe the linewidth of a phonon. The activation energy calculated from the ORM is 0.46 eV. Moreover, the motion of oxygen ion in Zn 2 GeO 4 is described in terms of the conventional fast-ion conductor.

The variations of equilibrium oxygen content with oxygen pressure and temperature were measured in copper doped double perovskite cobaltite PrBaCo2 −xCuxO5 +δ. The results of thermodynamic analysis show that oxygen pressure decrease and temperature increase both favor the appearance of oxygen vacancies in O2 structural positions. It is suggested that oxygen migration over O3 positions in double perovskite cobaltites occurs via mediation of O2 positions. Copper doping is shown to facilitate formation of oxygen vacancies in O2 positions, which is expected to be advantageous for enhanced oxygen ion transport.

The distribution of magnesium ions at the lanthanum and silicon sites in MgO-doped lanthanum silicate oxyapatite as well as the concentration of neutral lanthanum vacancies were determined using densities and chemical compositions of the doped samples. On the basis of the density data, it was found that magnesium ions are substituted at the silicon site as well as the lanthanum sites in the oxyapatite phase. Owing to the existence of neutral lanthanum vacancies, it was difficult to evaluate the number of the oxygen ions present, which are related to the oxygen ion conductivity of the compound, from the chemical compositions of the samples alone. Further, it was found that the fact that the total conductivity of MgO-doped lanthanum silicate oxyapatite depends on the MgO concentration as well as that of other defects could not be explained on the basis of conventional defect chemistry.

The diffusion in fast oxygen ion conductors is typically analyzed by isotope exchange experiments followed by secondary ion mass spectrometry (SIMS). This study demonstrates confocal Raman spectroscopy in combination with beveling of the specimen's surface as an interesting non-UHV alternative to SIMS. This simple and comparably inexpensive approach is shown to result in practically the same values for the diffusion properties as the SIMS technique. Thereby, the limitations of both techniques are compared for an easy understanding under which conditions they are applicable.

We have performed a first principle study of structural and phase stabilization of β -La 2 − x L x Mo 2 O 9 (L = Gd, Sm, Nd and Bi) and β -La 2 Mo 2 − y M y O 9 (M = Cr, W). The substitutional-site properties were discussed in terms of the empirical parameter, bond valence sums (BVS), which characterizes the interactions between atoms and its nearest-neighbor atoms and correlates well with the stability of the structure. We found that Gd, Sm and Nd atoms prefer the crystallographic sites with largest BVS values. The nonlinear dependence of cell parameter on W content in W-doped systems results from the nonlinear change in Mo/W–O bond length with W content. The decrease of cohesive energy and the deviation of BVS values from the expected values upon the Gd, Sm, Nd and W-doped concentration help us understand the experimentally observed stabilization of the β phase to lower temperatures in these doped system. The O ion diffusion properties in W-doped systems have been studied using the nudged elastic band method and the dimer method. We found that, W-doping leads to the obvious increase in the energy barriers of O ion concerted diffusion. In addition, there is a remarkable decrease in the difference of energy barriers between two diffusion channels involving O(1) ion, which sheds light on only one relaxation peak in the mechanical relaxation measurement in W-doped system, compared to undoped system.

Atomistic computer simulation has been used to predict the most energetically favourable migration pathways for oxygen ion transport in tetragonal La 2 NiO 4 . Both interstitial and vacancy mechanisms have been investigated. All of the vacancy mechanisms studied exhibited lower activation energies than the interstitial process. The lowest energy process allowed migration in the a – b plane with an activation energy of 0.35 eV, migration along the c -axis was predicted to have an activation energy of 0.77 eV and interstitial migration in the a – b plane was found to have an energy barrier of 0.86 eV (in agreement with available experimental data).

Based on the oxygen ion conductor La2Mo2O9, a series of Sm-doped substitutes (La2−xSmxMo2O9, x=0.1, 0.2, 0.3, 0.4) were prepared. The structure, influence of phase transition and oxygen ion conductivity were studied with DSC, HRTEM, high temperature and room temperature XRD, and complex impedance spectra. For comparison, Bi-doped substitutes (La2−xBixMo2O9, x=0.1, 0.2, 0.3, 0.4) were also prepared and studied. Experimental results showed that the substitution of La with appropriate amount of Sm can effectively stabilize the β-form of La2Mo2O9 at room temperature and inhibit its phase transition to α-form, and therefore presented the substitutes much higher ionic conductivity than the pristine La2Mo2O9. In addition, co-substitution of both La and Mo sites were achieved with Sm or Bi and W, and typical substitutes La2Mo1.7W0.3O9, La1.7Sm0.3Mo1.7W0.3O9 and La1.7Bi0.3Mo1.7W0.3O9 were obtained, which to some extent improved the ionic conductivity of La2Mo2O9, especially at lower temperatures.

Oxygen diffusion in layered cuprates La1.63Sr0.37CuO3.81 and LaSrCuO3.5 was simulated by molecular dynamics (MD) procedure. Two types of oxygen ions in the crystal lattice are characterized by different mobility at elevated temperatures (750–1000 K). Mechanistic features of oxygen transport are discussed.

This paper presents recent investigations of the defect, ion transport and surface properties of ABO3 perovskite-structured oxides using advanced computer simulation techniques. The principal methodologies are outlined which include techniques based upon energy minimisation and interatomic potentials, and quantum mechanical (QM) methods. The scope of computational studies of perovskites is illustrated by contemporary work on the topical systems LaGaO3, LaCoO3 and CaZrO3; the properties examined include mechanisms of oxygen ion migration, dopant–defect association, dynamics of proton diffusion and, finally, structures of oxide surfaces.

Possibility of utilization of CO-containing fuel in a fuel cell based on a solid oxide protonic conductor (SOFC(H + )) is demonstrated. Thermodynamic analysis of a methane fed SOFC(H + ) system is performed. It is stated that the fuel utilization depends on H 2 O/CH 4 mole ratio in the feeding fuel mixture and has a maximum at the ratio of about 2.6. It is stated that average EMF of the SOFC(H + ) is higher than that of an SOFC based on oxygen ion conductor under the same conditions and, hence, the maximum efficiency of the SOFC(H + ) system is about 15% higher than of the SOFC system based on oxygen ion conductor.

Electrotransport in oxides is an interesting phenomenon in two respects: (i) it gives insight into the microscopic mass and charge transport mechanisms in oxides, and (ii) due to the directed ionic fluxes, macroscopic phenomena such as demixing of an initially homogeneous multicomponent oxide can be studied. The electric field induces defect fluxes as a result of which ionic fluxes occur. Due to the different mobilities a concentration gradient will build up, and the initially homogeneous material becomes inhomogeneous. A formal analysis of the demixing phenomenon due to electrotransport is given for semiconducting oxide solutions and for doped oxygen ion conductors as well. Some experimental results and consequences for applications are discussed.

The defect structure and transport properties of complex perovskites with the general formula Sr3(Sr1+xNb2−x)O9−3x/2 have been studied through the use of thermogravimetry (TG), ac-conductivity and transport number measurements, comprising samples in the compositional range between Sr3(SrNb2)O9 (x=0) and Sr3(Sr1.5Nb1.5)O8.25 (x=1/2) (Sr/Nb ratio varying from 2 to 3). TG was used to measure the uptake of water, and the highest reversible water uptake was found for the end member Sr3(Sr1.5Nb1.5)O8.25 (x=1/2). The total conductivity (as a function of pH2O, pO2 and T) for a sample of composition Sr3(Sr1.4Nb1.6)O8.4 was fitted to a model based on Sr-acceptor defects compensated by doubly charged oxygen vacancies and protons. The partial conductivities found by transport number measurements support the modelled results. Oxygen ion conductivity dominates at high temperatures and protonic conductivity dominates below ∼550°C at ambient humidities. The enthalpy and entropy for the reaction of water with oxygen vacancies to form protons were found to be −160±5 kJ mol−1 and −166±5 J K−1 mol−1, respectively, for this sample. Oxygen ion and proton conductivities were also found to increase with Sr content. Moreover, the increase far exceeds the expected behaviour, and possible causes for this are discussed.

Chemically stable Sr0.97(Ti, Fe)O3−δ materials were prepared by a conventional solid state reaction procedure. Their transport properties were evaluated by electrochemical permeability experiments. Our results confirm that Fe additions yield SrTiO3 based materials with relatively good electronic and oxygen ion conductivities. However, the permeability experiments could not be fitted by a model behaviour derived on assuming that the ionic conductivity is independent of Po2, and a simple power law for the p-type contribution, σp=σp1(Po2)1/4.

A combination of atomistic simulation and quantum mechanical techniques have been used to investigate proton transport phenomena in LaMO3 perovskite-structured oxides. We examine the energetics of dopant substitution and of incorporation of water to yield hydroxyl groups. The energy barrier to proton transfer between neighbouring oxygen ions is evaluated by ab initio cluster calculations. The simulation results suggest that a key step for proton migration is the relaxation energy required for the two adjacent oxygen ions to acquire equivalent lattice environments preceding proton transfer.

Proton conducting thin films of SrZrO 3 and SrCeO 3 were fabricated by the pulsed laser ablation method using ArF excimer laser. The thin films of SrCeO 3 and SrZrO 3 were grown in the [100] direction on the SrTiO 3 (100) substrate and in the [211] direction on the MgO(100) substrate and on the Al 2 O 3 substrate. The Raman scattering spectra show that the thin films grown in the low P O 2 contain lots of oxygen ion vacancies compared to bulk crystals.

Oxygen ion conductivity was measured on a number of (Bi 2 O 3 ) 1− x (Pr 6 O 11 ) x systems from room temperature to 550°C. At x =0.05, the rhombohedral Bi 1.35 Pr 0.65 O 3 structure was found to be stable up to 550°C. At higher concentrations, a mixture of rhombohedral and possibly monoclinic type structures were determined, which at x =0.2 became fully “monoclinic”. High temperature X-ray powder diffraction confirmed the stability of the observed phases over the temperature range. The optimum ionic conductivity was found for the mixed phase and a value of 1.23×10 −2 s/cm was ascertained for x =0.15 at 450°C.

The nature of transport processes occurring during the growth of oxides at 1100°C on Fe-25 wt% Al and Ni-32 wt% Al has been investigated. Both materials develop protective α-Al2O3 scales which have been characterized by SEM, RHEED and Auger electron spectroscopy. Two-stage oxidation experiments have been conducted using 16O2 and 18O2 gases; imaging SIMS (secondary ion mass spectrometry) has been used to locate the different isotopic species. The SIMS data (profiles from areas as small as 3.5 μm×3.5 μm, and images with 0.1 μm lateral resolution) illustrate the complexity of the growth processes, and indicate areas where scale growth has taken place predominantly by cation or oxygen ion diffusion.

Ag 2+ ions are created in mixed Na + /Ag + and pure Ag + β alumina by X-ray irradiation. Whatever the silver content of the crystals, Ag 2+ are always trapped by the interstitial oxygen ions responsible for the charge compensation of the excess of monovalent cations. The effect of Frenkel defects and the origin of the lack of silver hyperfine structure are discussed.

The self-diffusion coefficient of the oxygen ion in antifluorite-cubic lithium oxide has been determined by means of the gas-solid isotope exchange and solid-phase analysis technique using 18 O as the tracer. Diffusion characteristics of the constituent ions in antifluorite-cubic crystal are discussed in comparison with those in fluorite-cubic crystals. The ionic conduction mechanism for Li 2 O is discussed in terms of the diffusivities of both ions.

Electrical conductivity measurements were made on Gd 2 (Zr 0.3 Ti 0.7 ) 2 O 7 as a function of temperature, oxygen fugacity and aliovalent dopant concentration using Ca and Ta. The oxygen ion conductivity was found to be dominated by oxygen vacancies generated both by intrinsic Frenkel formation and by impurity charge compensation. The Frenkel constant and oxygen vacancy mobility for Gd 2 (Zr 0.3 Ti 0.7 ) 2 O 7 were derived for the first time.

The structure of Li0.3125La0.5625MoO4 has been analyzed by the neutron powder diffraction technique and by the Rietveld method. The compound crystallizes with the symmetry of space group I41/a. The lattice parameters are a = 53350 (1), c = 11.7584 (3) A . The structure is of scheelite type. The La3+ ions are uniformly distributed on the sites 4b. The Mo6+ ions fully Occupy sites 4a and the O2- ions are located on sites 16f with x = 0.1413, y = 0.1226, and z = 0.2074. The refinement of the framework structure (no lithium included) gives low R factors (RN = 5.14, RP = 5.86, RW = 7.67, RE = 4.44 with anisotropic temperature factors). Refinements of trial models with the lithium included are peculiarly insensitive to the lithium positions, so that the location of these cations in the structure can only be postulated. A likely site for Li+ would be x⋍0.05, y⋍0.1, z⋍0.65 . In this position the Li+ would reside in the cavity of the La3+ cations and would be coordinated to five oxygen ions.

Structural analysis of superionic stabilized zirconias in the disordered state has been performed with single crystals of Zr(Ca)O2−x and Zr(Y)O2−x. Both integrated intensities of Bragf peaks and diffuse scattering were measured. There are preferential displacements of oxygen ions from the ideal positions of the fluorite structure along 〈100〉 directions. There are locally ordered regions, and our results indicate that the stabilizing ion and an oxygen vacancy are first neighbors in such regions, which is different from the arrangement if these regions are like CaZr4O9 as has been proposed by Allpress et al. This probably occurs to reduce local distortions, and to provide local charge balance.