Search

The Ba3InGa2O7.5 complex oxide, possessing the perovskite-related structure with structural oxygen vacancies, was first synthesized by the solid state method. The phase was found to be characterized by monoclinic symmetry (sp. gr. P2/c) with the following unit cell parameters: a = 7.942(1) Å, b = 5.868(5) Å, c = 18.201(6) Å, b = 91.52(9). Comprehensive investigations of electrical properties were carried out; ceramic material based on the complex oxide was shown to be a predominantly ionic conductor in the temperature range 450–900 oC. The conductivity is due to oxygen-ion transfer in dry conditions and oxygen-ion and proton transfer in wet atmosphere. The proton conductivity value is 4.5·10–5 S/cm, and the proton transport number is ~50% at 700 oC in wet air; at lower temperatures, proton transport becomes dominant. Prolonged treatment of the sample in water vapors below 450 oC leads to hydrolysis decomposition.

In present study, Fe-22Cr-4.5Al oxide dispersion strengthened ferritic alloys were fabricated using a pre-alloyed powder with different minor alloying elements, and their microstructures and tensile properties were investigated to develop the advanced structural materials for high temperature service components. Planetary-typed mechanical alloying and uniaxial hot pressing processes were employed to fabricate the Fe-Cr-Al oxide dispersion strengthened ferritic alloys. Microstructural observation revealed that oxide dispersion strengthened ferritic alloys with Ti, Zr additions presented extremely fine micro-grains with a high number density of nano-scaled oxide particles which uniformly distributed in micro-grains and on the grain boundaries. These oxide particles were confirmed as a fine complex oxide, Y2Zr2O7. These favorable microstructures led to superior tensile properties than commercial ferritic stainless steel and oxide dispersion strengthened ferritic alloy with only Ti addition at elevated temperature.

Strontium and cobalt-free LaNi0.6Fe0.4O3–δ is considered one of the most promising electrodes for solid-state electrochemical devices. LaNi0.6Fe0.4O3–δ has high electrical conductivity, a suitable thermal expansion coefficient, satisfactory tolerance to chromium poisoning, and chemical compatibility with zirconia-based electrolytes. The disadvantage of LaNi0.6Fe0.4O3–δ is its low oxygen-ion conductivity. In order to increase the oxygen-ion conductivity, a complex oxide based on a doped ceria is added to the LaNi0.6Fe0.4O3–δ. However, this leads to a decrease in the conductivity of the electrode. In this case, a two-layer electrode with a functional composite layer and a collector layer with the addition of sintering additives should be used. In this study, the effect of sintering additives (Bi0.75Y0.25O2–δ and CuO) in the collector layer on the performance of LaNi0.6Fe0.4O3–δ-based highly active electrodes in contact with the most common solid-state membranes (Zr0.84Sc0.16O2–δ, Ce0.8Sm0.2O2–δ, La0.85Sr0.15Ga0.85Mg0.15O3–δ, La10(SiO4)6O3–δ, and BaCe0.89Gd0.1Cu0.01O3–δ) was investigated. It was shown that LaNi0.6Fe0.4O3–δ has good chemical compatibility with the abovementioned membranes. The best electrochemical activity (polarization resistance about 0.02 Ohm cm2 at 800 °C) was obtained for the electrode with 5 wt.% Bi0.75Y0.25O1.5 and 2 wt.% CuO in the collector layer.

BaBiO3 is an oxide perovskite with a wide variety of interesting properties. It was expected that the compound would behave like a metal. However, experiments revealed that BaBiO3 is not metallic, which started an extensive debate about the mechanism responsible for this insulating behavior. The two most important conjectures in this debate are charge disproportionation of the Bi ion into 3+ and 5+ cations and bond hybridization of the Bi 6s and O 2p orbitals. Both mechanisms induce a breathing mode of the oxygen octahedra, which is experimentally observed in single crystals and thin films. Recently, ultra-thin BaBiO3 films were studied with the aim of suppressing the breathing mode, which was expected to result in re-emergence of metallicity. However, this expectation was not confirmed so far. Furthermore, theoretical calculations predict that BaBiO3 becomes a topological insulator (TI) when doped with electrons. Since high-temperature superconductivity was observed when doping the compound with holes, an interface between a superconductor and a TI can be established within the same parent compound. In this Review, we discuss the theoretical and experimental findings concerning the mechanism responsible for the unexpected insulating behavior of BaBiO3 for both single crystals and thin films. An overview is given of the current state of the art and the experimental challenges of achieving an oxide topological insulating state in BaBiO3.

Sm0.9Ca1.1Fe0.7Co0.3O4-δ oxide with the K2NiF4-type structure was prepared using a glycerin-nitrate technique. The XRD pattern of Sm0.9Ca1.1Fe0.7Co0.3O4-δ was refined by the Rietveld method within an orthorhombic structure (space group Bmab). The electrical conductivity, Seebeck coefficient, and thermal expansion of Sm0.9Ca1.1Fe0.7Co0.3O4-δ were measured depending on temperature in air. The change of oxygen nonstoichiometry determined by TGA in air does not exceed 0.01. The oxygen content in Sm0.9Ca1.1Fe0.7Co0.3O4-δ determined by the reduction in a hydrogen flux is equal to 3.96 ± 0.01. The positive value of Seebeck coefficient indicates that the predominant charge carriers in the oxide studied are electron holes.

Epitaxial PrBaCo2O5+δ (PBCO, 0≤ δ ≤ 1) thin films were deposited by pulsed laser deposition. The structural and electrical properties of the films were characterized at high temperatures in reduced environments. X-ray diffraction scans at high temperature in reduced environment show potential structural transitions of PBCO as evidenced by both a large (Δl = 0.335 nm) expansion of the out-plane (c-axis) lattice, due to thermal and chemical expansion, and a step in the expansion of the c-axis lattice parameter. These transitions indicate the presence of oxygen vacancy ordering as the oxygen content in the films is reduced. Resistivity measurements under the same environments also show evidence of sharp transitions related with the structural transformations. This study helps the understanding of the structure-property relationship of PBCO at high temperature and provides important technological information to utilize these materials for solid oxide fuel cell at intermediate temperatures.

The material BaBiO3 is known for its insulating character. However, for thin films, in the ultra-thin limit, metallicity is expected because the oxygen octahedra breathing mode will be suppressed as reported recently. Here, we confirm the influence of the oxygen breathing mode on the size of the band gap. The electronic properties of a BaBiO3 thickness series are studied using in-situ scanning tunneling microscopy. We observe a wide-gap (EG > 1.2 V) to small-gap (EG ≈ 0.07 eV) semiconductor transition as a function of a decreasing BaBiO3 film thickness. However, even for an ultra-thin BaBiO3 film, no metallic state is present. The dependence of the band gap size is found to be coinciding with the intensity of the Raman response of the breathing phonon mode as a function of thickness.

Photocatalysts are the most important technology in air pollution removal and the detoxification of organic materials. Doping and complexation are among the most used methods to improve the efficiency of photocatalysts. Titanium dioxide and zinc oxide nanomaterials are widely used materials for photocatalysts and the degradation of toxic materials. Their mixed structure can be fabricated by many methods and the structure affects their properties. Nanofibers are efficient materials for photocatalysts due to their vertically formed structure, which improves the charge separation of photoelectrons. We fabricated them by an electrospinning process. A precursor consisting of titanium 4-isopropoxide, zinc acetate dihydrate and polyvinylpyrrolidone was used as a spinning solution for a mixed structure of titanium dioxide and zinc oxide with different molar ratios. They were then calcined, crystallized by heat treatment and analyzed by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM) and energy-dispersive spectroscope (EDS). After annealing, the average diameters of the Ti–Zn complex oxide nanofibers were 237.6–278.6 nm with different salt ratios, and multiple crystalline structures were observed, namely TiO2, ZnO, ZnTiO3 and Zn2TiO4. We observed the photocatalytic performance of the samples and compared them according to the photodegradation of methylene blue. The methylene blue concentration decreased to 0.008–0.650 after three hours, compared to an initial concentration of 1, with different metal oxide structures.

Oxide dispersion-strengthened (ODS) materials contain homogeneous dispersions of temperature-stable nano-oxides serving as obstacles for dislocations and further pinning of grain boundaries. The strategy for dispersion strengthening based on complex oxides (Y-Hf, -Zr, -Ce, -La) was developed in order to refine oxide dispersion to enhance the dispersion strengthening effect. In this work, the strengthening of EUROFER steel by complex oxides based on Y and elements of the IIIB group (lanthanum, scandium) and IVB group (cerium, hafnium, zirconium) was explored. Interparticle spacing as a dispersoid characteristic appeared to be an important factor in controlling the dispersion strengthening contribution to the yield strength of ODS EUROFER steels. The dispersoid size and average grain size of ODS EUROFER steel were altered in the ranges of 5−13 nm and 0.6−1.7 µm, respectively. Using this strategy, the yield strength of the prepared alloys varied between 550 MPa and 950 MPa depending on the doping element.

To precisely control the characteristics of complex oxides by heat treatment, the effect of FeO on the interfacial reactions that occur between an Fe–Mn–Si alloy and CaO–SiO2–Al2O3–MgO–MnO–FeO oxide was studied and clarified. Eight types of diffusion couples with different compositions of oxides were produced using a confocal scanning laser microscope (CSLM). The morphologies of the alloy–oxide interfaces and the changes in their chemical compositions with isothermal heating at 1273 and 1473 K for 10 h were investigated. A modified dynamic calculation model was established and verified to achieve better understanding on the interfacial reaction mechanism between the Fe–Mn–Si alloy and the multicomponent oxide with different FeO content during isothermal heating. The results showed that during isothermal heating at 1273 and 1473 K, “solid–solid” and “solid–liquid” alloy–oxide reactions occurred in the A-1-x and A-2-x diffusion couples, respectively. The interfacial alloy–oxide reactions were enhanced by increasing the initial FeO content in the oxide and the heating temperature. The particle precipitation zone (PPZ), Mn-depleted zone (MDZ) and Si-depleted zone (SDZ) widths in the A-1-x and A-2-x diffusion couples after heating also showed a positive correlation with the increase in the initial FeO content in the oxide, as well as the size and number of MnO·SiO2 inclusions. The diffused oxygen from the oxide reacting with elemental Mn and Si in the alloy plays a dominant role in the A-1-x diffusion couple during heating, whereas for A-2-x, the dominant reaction is between elemental Si in the alloy and MnO in the oxide.