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The crystal structure, oxygen nonstoichiometry, and electrical conductivity in PrBa1 – xCo2O6 – δ cobaltites with double perovskite structure are studied. It is shown that defective cobaltites within region of homogeneity 0 < х ≤ 0.1 have a tetragonal structure (space group P4/mmm) with parameters ap × аp × 2аp, where аp ~ 3.8 A. Coulometric titration is used to measure the content of oxygen in oxides over a wide range of temperatures and oxygen pressures in the gas phase, to calculate the concentrations of electronic defects, and to determine the limits of the thermodynamic stability of composition х = 0.1. It is established that increasing the concentration of cationic vacancies in the barium sublattice reduces the mobility of the hole charge carriers and contributes to a drop in the thermal expansion coefficient.

The coherent potential approximation is applied for studying the electronic spectrum features in cubic perovskite-like ferrite La1-xSrxFeO3-δ with ionic compensation of strontium acceptors at 0 ≤ x ≤ 0.75. The energy characteristics and magnetic moments calculated with accounting for electron correlations agree with the experimental data. The concentration dependent trends in electrical properties are shown to reflect combined effects of formation of vacancy bands, hybridization and splitting of Fe 3d states in the vicinity of the Fermi energy.

The development of advanced and cost-effective methods is of prime importance for manufacturers of high purity gases. In this paper a new strategy in the development of gas flow purification technologies is described, where instead of adsorbents reactants are used, in which not only the surface is used in gas capturing but the entire volume of the material. Moreover, the reactants are activated in the gas flow by a controlled mechanical tool, which keeps the sorption kinetics at the required highest level and reduces the unproductive losses of the consumed reactant almost to zero. The advantages of the method are demonstrated with the examples of two novel gas purification units that are distinguished with uncomplicated design, serviceability and ultimately high purification efficiency.

The solid solution Sr0.5Ca0.5Mn1–xVxO3–δ (0 ≤ x ≤ 0.125) has been obtained via a citrate-nitrate synthesis route. Powder X-ray diffraction (XRD) data for x = 0, 0.025 and 0.05 reveal the formation of perovskite-type orthorhombic structure with Pbnm space group (SG). Further increase of the vanadium content results in the appearance of the tetragonal crystal structure (SG I4/mcm) so that the composition of x = 0.075 is formed by the orthorhombic and tetragonal phase constituents in the 1:3 vol ratio. The single-phase sample at x = 0.1 is characterized by tetragonal symmetry of its unit cell. The comparison between the calculated (XRD) and pycnometric density values is indicative of 6-fold oxygen coordination of vanadium dopants. High-temperature electrical conductivity (σ) and Seebeck coefficient (S) measurements give evidence to the presence of electronic charge carriers that can be associated with Mn3+ cations appearing in response to vanadium doping. The largest thermoelectric power factor S2σ = 1.5 µW·K−2·cm−1 is attained in the two-phase composition x = 0.075 at 450 °C.

The electrical conductivity (σ) of Ca1–xPrxMnO3–δ (х = 0–0.15) manganites with a perovskite-like structure has been measured by the four probe method in air at temperatures (T) from 320 to 1220 K. The results have been analyzed in terms of a model of small adiabatic polarons. The observed decrease in σ with increasing T is primarily due to the decrease in carrier concentration as a result of Mn3+ disproportionation into Mn2+ and Mn4+. The polaron mobility ranges from 0.2 to 1.2 cm2/(V s) and decreases with increasing praseodymium content.

The Seebeck coefficient (S) of Ca1–x Pr x MnO3–δ (х = 0, 0.05, 0.10, 0.15) manganites with a perovskite-like structure has been measured in air at temperatures (T) from 300 to 1200 K. The negative sign of their S indicates that all of the samples have n-type conductivity. The observed increase in the magnitude of the Seebeck coefficient with increasing T is interpreted in terms of small-polaron transport with allowance for the decrease in Mn3+ concentration as a result of the disproportionation reaction 2Mn3+ = Mn2+ + Mn4+. Based on a theoretical analysis of experimental S(T) data, we calculated equilibrium constants for the disproportionation reaction, carrier concentration, and the concentration of sites available for carrier migration as functions of temperature. It has been shown that, for an adequate analysis of electron hopping and calculation of the Seebeck coefficient of the electron-doped manganites, the spin state of the Mn4+ ions should be taken into account.

The chemical potential of oxygen ΔμO(δ,y,T) relative to the standard state is calculated from experimental data for equilibrium oxygen content in Ca0.6–уSr0.4LaуMnO3–δ at different values of temperature and oxygen partial pressure in the gaseous phase. The respective values of partial molar enthalpy Δ H ¯ O ( δ , y ) and entropy Δ S ¯ O ( δ , y ) are derived from the linear plots for ΔμO(δ,y,T) vs. temperature. Based on the ideal solution approximation, the equations are obtained that show interrelation of Δ H ¯ O ( δ , y ) and Δ S ¯ O ( δ , y ) with thermodynamic parameters of defect formation reactions and concentration of defects. It is shown that thermal excitation of Mn4+ cations considerably impacts equilibration of defect species in the crystal structure of Ca0.6–уSr0.4LaуMnO3–δ.

The chemical potential of oxygen ΔμO relative to its standard state in the gas phase was calculated from the experimental dependences of the oxygen content in various polymorphic modifications of Ca0.9Pr0.1MnO3–δ on the partial pressure and temperature. The partial molar enthalpy \(\Delta {\overline H _O}\) and entropy \(\Delta {\overline S _O}\) of oxygen were obtained from the linear temperature dependences of ΔμO. Based on the ideal solution approximation, \(\Delta {\overline H _O}\) and \(\Delta {\overline S _O}\) were correlated with the enthalpies and entropies of the defect formation reactions, the concentrations of manganese cations, and the oxygen nonstoichiometry. The thermal excitation of Mn4+ cations was shown to substantially affect the thermodynamic functions of oxygen.

The genesis of the electronic spectrum and magnetic properties of a high-temperature cubic phase of SrFeO3–δ with the disordered distribution of oxygen vacancies under the variation of their concentration has been studied in the coherent-potential approximation within the LDA + U formalism. Experimental tendencies of the fundamental electron-energy and magnetic characteristics in SrFeO3–δ under the variation of oxygen nonstoichiometry within the homogeneity region, 0 ≤ δ ≤ 0.5, have been described.

The content of oxygen in Ca1−x Pr x MnO3−δ (x = 0.1) material with perovskite-like structure is determined at 750–950°C and oxygen partial pressures in the gas phase from 3 × 10−6 to 0.55 atm. The regions of existence of orthorhombic, tetragonal, and cubic structural modifications are determined. The equilibrium constants, enthalpies, and entropies of reactions of the formation of defects are determined, allowing us to describe the experimental δ ( $${p_{{O_2}}}$$ ,Т) dependences accurately and calculate the concentrations of manganese ions. It is shown that a change in Ca0.9Pr0.1MnO3–δ structure has a considerable effect on the thermodynamic functions of reactions of the formation of defects.

Manganites Ca1–х Pr х MnO3–δ, where 0 ≤ х ≤ 0.15 were studied. The compounds have orthorhombic structure (space group Pnma) at ambient temperature, which consecutively transforms on heating in air into phases with tetragonal I4/mcm and cubic 000000 structure. Increase in praseodymium concentration leads to higher phase transition temperatures, lower heat of structural transformations, more narrow homogeneity range of oxygen, and a wider temperature interval of tetragonal I4/mcm phase existence.

During the past decade, ab initio electronic structure methods have been extensively developed and employed for properties analysis of perovskites ABO3–δ, where A is a large cation and B is typically a 3d metal cation of smaller size. The perovskite structure is capable to withstand ample cation substitutions in both A and B sub-lattices and to simultaneously accommodate large amount of oxygen vacancies (δ). The cation and anion defects result in considerable changes in electronic spectrum features and ensuing properties. In the variety of electronic structure calculation methods, the coherent potential approximation (CPA) is a special approach for studies of systems with disordered defects. The method is designed in order to overcome a number of restrictions that arise at employment of supercells such as defect ordering, limitations for defect types and concentrations, a drastic increase in calculation time with defect concentration, etc. The recently developed implementation of the CPA can be used for calculations of electronic spectrum and properties of solid state systems, including strongly correlated ones with an arbitrary concentration, arrangement and type of atomic structural defects. In this brief review, we consider the capabilities and restrictions of classical CPA-combined methods and represent a novel CPA methodology for the case study of electronic spectra and magnetic moments in several perovskite related disordered ferrites including SrFeO2.5, SrFeO3−δ and solid solutions La1−xSrxFeO3−δ. These complex oxides with strong electronic correlations attract attention as inexpensive, environmentally friendly and robust materials for applications in high-temperature redox technologies, fuel cells, self-cleaning photocatalysis, water splitting, hydrogen and solar power engineering.

55Mn NMR spectra in the magnetically ordered state in Sr0.98La0.02MnO3 manganite have been obtained and the magnetic susceptibility has been measured. It has been shown that the microscopic phase separation into the antiferromagnetic matrix and ferromagnetic clusters, which can be presented as magnetic polarons, is observed in the long-range magnetic order region.

The electronic structure and magnetic properties of the high-temperature cubic phase of strontium ferrite SrFeO2.5 with the disordered location of oxygen vacancies have been calculated using the coherent potential method. The semiconductor character of the electronic spectrum of SrFeO2.5 is observed only at certain types of disordering of vacancies over the oxygen sublattice, which makes it possible to choose among structural models of the high-temperature phase proposed on the basis of experiments.

The perovskite-like electron doped manganites Ca 0.6− у Sr 0.4 La у MnO 3− δ (0 ⩽ y ⩽ 0.15) were synthesized in order to study oxygen content variations with composition, temperature and oxygen partial pressure. The samples are characterized with orthorhombic Pnma structure at 0 у I 4/ mcm structure at у ⩾ 0.13 according to room temperature powder X-ray diffraction (XRD). The high-temperature data of XRD in air show transition to cubic Pm 3 ¯ m structure at heating above 550 °С. The variations of oxygen content in Ca 0.6− у Sr 0.4 La у MnO 3− δ with temperature and oxygen pressure were measured using thermogravimetry and coulometric titration at temperatures between 650 and 950 °С in the oxygen pressure range 10 −4 –0.7 atm. The oxygen nonstoichiometry δ changes in Ca 0.6− у Sr 0.4 La у MnO 3− δ are observed to considerably decrease with the increase in lanthanum content. In order to explain the nonstoichiometry data, a thermodynamic model is developed based on defect formation reactions 2Mn 3+ + V O + ½O 2 = 2Mn 4+ + O 2− and 2Mn 4+ = Mn 3+ + Mn 5+ . The respective equilibrium constants, defect formation enthalpies and entropies are obtained. The concentrations of different defects are calculated as functions of temperature, oxygen pressure and lanthanum content. The high-temperature conductivity measurements are carried out for independent verification of the suggested model.

The incorporation of tantalum cations in mixed-conducting SrFe1-xTaxO3−δ (x = 0.03 − 0.10) results in the formation of single cubic perovskite-like phases in oxidizing atmospheres while under reducing conditions phase separation is observed, accompanied with an appearance of brownmillerite-type nanodomains on the background of the perovskite-like matrix. For SrFe0.97Ta0.03O3−δ after reduction, the x-ray and electron diffraction studies combined with transmission electron microscopy evidence the formation of approximately 30 vol.% brownmillerite phase with an average domain size of 20–40 nm. The oxygen partial pressure dependencies of the total conductivity in the \( {p}_{{\mathrm{O}}_2} \) range from 10−20 to 0.5 atm at 700–950 °C show that the electron transport parameters remain virtually independent on the dopant content and domain structure. Contrary to the materials with higher dopant content, however, the ion conduction in SrFe0.97Ta0.03O3−δ tends to substantially increase on redox cycling. This behavior was attributed to the brownmillerite domain disintegration and rearrangement, induced by cyclic formation and disappearance of oxygen vacancies.

The formation of fluorite-like solid solutions near composition Ln 5 Mo 3 O 16+ δ is observed in binary systems Ln 2 O 3 –MoO 3 , where Ln = Nd and Pr, at synthesis in the air. The oxide ratio Ln 2 O 3 :MoO 3 within homogeneous solubility range varies from 3:4 to 7:8 and from 9:11 to 7:8 for neodymium and praseodymium oxides, respectively. The oxygen pressure dependent isotherms in Ln 5 Mo 3 O 16+ δ demonstrate mixed, oxygen-ion and electron, character of conductivity. The ion transference numbers change from 0.16 to 0.92 at variations of oxygen pressure and temperature within 10 –5 –0.5 atm and 700–950 °С, respectively. The oxygen ion and electron components of conductivity are characterized by the activation energy of about 1.0 and 1.4 eV, respectively. It is argued that the ion contribution is related with jumps of off-stoichiometric oxygen over structural interstitials in the fluorite-like crystalline lattice.

The electrical conductivity, thermopower, DTA and TG measurements were carried out at heating of CaMnO3−δ in air within the temperature range 300–1300 K. The concentration of electrons in CaMnO3−δ at δ → 0 was derived from the defect model based on simultaneous reactions of oxygen exchange and thermal excitation of electrons. The calculation results and experimental data for electrical conductivity were combined in order to obtain drift mobility of the charge carriers at 700–900 K. The mobility activation energy is found to be about 0.07 eV. It is shown that electron transport properties in CaMnO3 at elevated temperatures can be explained in terms of activated jumps of n-type adiabatic small polarons. The relatively small mobility is explained by strong localization of the polarons on manganese sites.

The experimental data for equilibrium oxygen content were used in order to extract increments of partial molar thermodynamic functions of oxygen with changes of oxygen stoichiometry in calcium manganite CaMnO3-δ. It is shown that along with the oxygen exchange reaction, thermal excitation of Mn4+ cations plays an important role in equilibration of charged manganese species that appear in response to the loss of oxygen at heating. The interrelation of partial molar enthalpy and entropy of oxygen with electron and ion defect formation parameters is obtained in approximation of the point defect model. The nearly linear changes of oxygen partial molar enthalpy are shown to directly reflect thermally driven changes in concentration of Mn3+ cations. © Springer-Verlag Berlin Heidelberg 2013.

Structural features, oxygen non-stoichiometry and transport properties are studied in the oxide series SrFe{sub 1-x}Ta{sub x}O{sub 3-{delta}}, where x=0.2, 0.3 and 0.4. X-ray diffraction and electron microscopy data evidence formation of the inhomogeneous materials at x=0.3 and 0.4, which include phase constituents with a cubic perovskite and a double perovskite structure types. The composition, the amount and the typical grain size of the phase inhomogeneities are shown to depend both on doping and oxygen content. The increased oxygen-ion conductivity is observed in oxygen depleted materials, which is explained by the increase in the amount of cubic perovskite-like phase and development of interfacial pathways favorable for enhanced oxygen ion transport. - Graphical abstract: The structural studies, oxygen content and conductivity measurements suggest that oxygen depletion from the double perovskite phase constituent of SrFe{sub 1-x}Ta{sub x}O{sub 3-{delta}} for x>0.2 is accompanied by formation of pathways for fast ion transport. Black-Small-Square Highlights: Black-Right-Pointing-Pointer The double perovskite type regions are shown to exist in SrFe{sub 1-x}Ta{sub x}O{sub 3-{delta}}. Black-Right-Pointing-Pointer The oxygen depletion is accompanied with phase separation. Black-Right-Pointing-Pointer The phase separation favors formation of pathways for enhanced oxygen ion transport.

A defect equilibrium model is suggested for CaMnO3 − δ based on oxygen non-stoichiometry and conductivity data. The model includes reactions of oxygen exchange and thermal excitation of electrons. The respective equilibrium constants, enthalpies and entropies for the reactions entering the model are obtained from the fitting of the calculated and experimental data for oxygen non-stoichiometry. The energy parameters obtained from the model and variations in the concentration of manganese species enable explanation of temperature and oxygen pressure dependencies of thermopower and conductivity within frameworks of a small polaron type model.

The oxygen content in CaMnO3–δ is studied by a coulometric titration technique depending on temperature and oxygen partial pressure variations in the ambient atmosphere. The δ–T phase diagram is derived from the obtained data where single-phase fields are outlined for orthorhombic, tetragonal, and cubic structures. The thermal expansion coefficient considerably larger in the cubic phase than in the tetragonal one is related with formation of large Mn3+ cations at depletion of oxygen from the crystalline lattice. Negative thermopower is explained by concomitant reactions of oxygen loss and charge disproportionation, $$ {\hbox{2M}}{{\hbox{n}}^{{{4 + }}}}{\hbox{ = M}}{{\hbox{n}}^{{{3 + }}}}{\hbox{ + M}}{{\hbox{n}}^{{{5 + }}}}{ } $$ . The forbidden energy gap in CaMnO3–δ is evaluated to be about 0.5 eV.

The content of oxygen in Ca0.6 − ySr0.4LayMnO3 − δ, where y = 0 and 0.05, was determined by coulometric titration over the temperature range 650–950°C at oxygen partial pressure in the gas phase varied from 10−4 to 1 atm. The results were used to calculate the partial molar enthalpy, Δ\( \bar H \)O(δ), and entropy, Δ\( \bar S \)O(δ), of oxygen in manganites. Changes in the Δ\( \bar H \)O(δ) and Δ\( \bar S \)O(δ) dependences caused by the introduction of lanthanum are evidence of the formation of local clusters of the double perovskite type in the Ca0.6Sr0.4MnO3 − δ matrix.

The oxygen vacancies distribution in the rigid lattice and the thermally activated motion of oxygen atoms are studied in La{sub 1-x}Sr{sub x}Ga{sub 1-x}Mg{sub x}O{sub 3-x} (x=0.00; 0.05; 0.10; 0.15 and 0.20) compounds. For that {sup 71}Ga, {sup 25}Mg and {sup 17}O NMR was performed from 100 K up to 670 K, and ion conductivity measurements were carried out up to 1273 K. The comparison of the electric field gradients at the Ga- and Mg-sites evidences that oxygen vacancies appear exclusively near gallium cations as a species trapped below room temperature in local clusters, GaO{sub 5/2}-{open_square}-GaO{sub 5/2}. These clusters decay at higher temperature into mobile constituents of the structural octahedra Ga(O{sub 5/6{open_square}1/6}){sub 6/2}. At the same time, the nearest octahedral oxygen environment of magnesium cations persists at different doping levels. The case of two adjacent vacant anion sites is found highly unlikely within the studied doping range. The thermally activated oxygen motion starts to develop above room temperature as is observed from both the motional narrowing of {sup 17}O NMR spectra and the {sup 17}O nuclear spin-lattice relaxation rate. The obtained results show that two types of motion exist, a slow motion and a fast one. The former is a long-rangemore » diffusion whereas the latter is a local back and forth oxygen jumps between two adjacent anion sites. These sites are strongly differentiated by the probability of the vacancy formation, like the vacant apical site and the occupied equatorial site in the orthorhombic compositions x

The conductivity is measured in the series of solid solutions SrFe 1 − x Nb x O 3 − δ , where x = 0.05, 0.1, 0.2, 0.3, 0.4, within the oxygen partial pressure limits 10 −18 –0.5 atm and temperature range 650–950 °C. The contributions to the total conductivity from oxygen ions, electrons and electron holes are obtained based on their different pressure dependences. The doped derivative with x = 0.1 is found to be a singular composition where ion conductivity attains a maximal value while activation energy for ion transport is minimal. This peculiar behavior is attributed to formation of favorable microstructure in the oxide. The deeper doping results in deterioration of ion transport, which is explained by oxygen vacancy filling. It is shown that replacement of iron for niobium favors enhanced thermodynamic stability towards reduction. The oxygen permeability is evaluated from the conductivity data, and it achieves rather high values in the doped derivatives. These oxides can, therefore, be recommended for further evaluation as oxygen separating membrane materials for partial oxidation of natural gas.

The special features of the structure, electrophysical properties, and oxygen nonstoichiometry of new double perovskites PrBaCo2 − xCuxO5 + δ were studied. Within the homogeneity region with respect to copper 0 < x ≤ 1, solid solution samples had an orthorhombic structure (space group Pmmm) with the parameters ap × 2ap × 2ap, where ap ≈ 3.8 A. The oxygen nonstoichiometry of PrBaCo2 − xCuxO5 + δ changes as the copper content increases approximately as δ ≈ 0.85 − x/2. The content of oxygen was measured by coulometric titration over wide temperature and oxygen pressure ranges. The partial thermodynamic functions of labile oxygen were calculated and the limits of the thermodynamic stability of the solid solution were established.

The influence of doping with niobium on the structure and oxygen nonstoichiometry of strontium ferrite SrFe1 − x Nb x O3 − δ (x = 0.05, 0.1, 0.2, 0.3, and 0.4) was studied. The content of oxygen in the doped derivatives was determined by coulometric titration as a function of temperature (650–950°C) and oxygen partial pressure in the gas phase (10−4−1 atm). The partial molar enthalpies Δ\( \bar H_O \)(x, δ) and entropies Δ\( \bar S_O \)(x, δ) of oxygen in SrFe1 − x Nb x O3 − δ were calculated. An analysis of Δ\( \bar S_O \)(x, δ) dependences showed that the model of a random distribution of ions and vacancies over accessible sites in the oxygen sublattice allowed the experimental data to be described satisfactorily. An increase in the partial enthalpy Δ\( \bar H_O \)(x, δ) as nonstoichiometry δ decreased was indicative of weak repulsive interactions between oxygen ions in the structure of SrFe1 − x Nb x O3 − δ.

Changes in the electronic structure and magnetic characteristics of Sr2FeMO6 double perovskites were studied by the FLAPW-GGA ab initio band structure method in relation to the type of the cation M = Sc, Ti, ..., Ni, Cu.

The conditions for preparation of Ce0.9Y0.1O2 (CYO) oxide coatings on La0.8Sr0.2MnO3 (LSM) ceramic substrates by screen printing were investigated. The CYO compound was synthesized by the pyrolysis of polymer-salt composites with the aim of producing submicron powders with a uniform size distribution. Transmission electron microscopy of the microstructure of the CYO compound synthesized with ethylene glycol revealed that the synthesis product consists of ultrafine crystalline particles with an average size of 5–15 nm. The use of CYO nanopowders made it possible to prepare rather dense single-layer coatings on LSM substrates. It was demonstrated that annealing of the coatings at high temperatures leads to the recrystallization and coarsening of particles.

The complex oxides in the series SrFe 1 − x W x O 3 − δ were synthesized and attested to have cubic structure. The oxygen content was measured by coulometric titration technique, and electrical conductivity was measured by four-probe d.c. method in the oxygen partial pressure range 10 − 18 –0.5 atm and at temperatures 650–950 °C. Thermal expansion tests were performed in air within temperature interval 20–1000 °C. The partial molar thermodynamic functions of labile oxygen ions were calculated using coulometric titration data. Conductivity analysis was utilized to separate partial contributions from oxygen ions, n-and p-type electron charge carriers. The concentration and mobility of p-type charge carriers were calculated by combining data from oxygen content and conductivity measurements. It is shown that partial replacement of iron for tungsten results in a strong disordering of the oxygen sub-lattice that renders the perovskite to brownmillerite phase transition suppressed. The observed ion conductivity level in the sample x = 0.1 at T

Using the full-potential linearized augmented plane-wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange-correlation potential, we studied spin polarization induced by replacement of oxygen atoms by non-magnetic 2p impurities (B, C and N) in non-magnetic cubic SrMO 3 perovskites, where M=Ti, Zr and Sn. The results show that the magnetization may appear because of the spin–split impurity bands inside the energy gap of the insulating SrMO 3 matrix. Large magnetic moments are found for the impurity centers. Smaller magnetic moments are induced on the oxygen atoms around impurities. It is shown that SrTiO 3 :C and SrSnO 3 :C should be magnetic semiconductors while other compounds in this series (SrTiO 3 :B, SrTiO 3 :N and SrZrO 3 :C) are expected to exhibit magnetic half-metallic or pseudo-half-metallic properties.

The full-potential LAPW method in the local spin-density approximation (LSDA) is applied to the theoretical search for new magnetic semimetals on the basis of a nonmagnetic SrSnO3 semiconductor doped with magnetic ions M = Mn, Fe, Co. It is found that, in contrast to Sr2SnMnO6 (a ferromagnetic semiconductor) and Sr2SnCoO6 (a ferromagnetic metal), Sr2SnFeO6 perovskite is a ferromagnetic semimetal: its electronic spectrum has a band gap (∼0.7 eV) for the low-spin subsystem and is metal-type for the high-spin subsystem. For isoelectronic analogs SrSnO3-CaSnO3 and BaSnO3, it is shown that their doping by iron (Ca2SnFeO6 and Ba2SnFeO6 compositions) also makes it possible to realize the semimetal state of these systems. It is assumed that A(Sn1−x Fex)O3 (A = Ca, Sr, Ba) solid solutions can become the first representatives of a new group of materials for spin electronics.

The oxygen nonstoichiometry, electrical conductivity and Seebeck coefficient of perovskite-related SrFe1−xGaxO3−δ ( x = 0 – 0.2 ) and SrFe1−xAlxO3−δ ( x = 0.1 – 0.3 ) were studied in the temperature range 923–1223 K at oxygen partial pressures varying from 10−20 to 0.3 atm. The substitution of iron with gallium was found to promote long-range ordering of oxygen vacancies, resulting in the perovskite → brownmillerite transition at moderate oxygen pressures, and to decrease the mobility of the p-type electronic charge carriers. Opposite tendencies are observed for aluminum doping, which causes a higher oxygen nonstoichiometry in oxidizing atmospheres. As suggested by atomistic simulations of highly oxygen-deficient ferrite lattices, this behavior is associated with oxygen-vacancy trapping near Al3+ having energetically favorable tetrahedral coordination, whereas Ga3+ cations with preferential octahedral coordination in the perovskite lattice tend to repulse vacancies towards oxygen sites surrounded by iron and thus destabilize the structure. The relatively low hole mobility, with activation energies of 0.18–0.33 eV, indicates a small-polaron conduction mechanism. Under reducing conditions the oxygen content and ionic transport in brownmillerite-type polymorphs of SrFe1−xGaxO3−δ, exhibiting a relatively wide range of oxygen stoichiometry variation, are both lower compared to the Al-containing materials characterized by the co-existence of perovskite- and brownmillerite-like domains.

The parameters of the electronic structure and hyperfine interactions in perovskite SrFeO3 were determined for different types of spin and charge states by ab initio discrete variations within the cluster model. The best agreement with experiment was achieved when the charge disproportionation effect {[Fe4+O6]8− + [Fe4+O6]8−} → {[Fe3+O6]9− + [Fe5+O6]7−} was taken into account.

The total conductivity and oxygen deficiency of partially substituted strontium ferrite, SrFe0.9M0.1O3-δ (M=Cr, Ti, Al), at 700-950°C were measured depending on oxygen partial pressure varying in ranges 10-19-0.5 and 10-5-0.5 atm. The partial contributions of n- and p-type electronic charge carriers and oxygen ions to the electrical transport were determined analyzing the total conductivity vs. oxygen pressure dependencies. Additions of all dopants studied in this work are found to extend the cubic perovskite phase stability range and to improve oxygen transport in the intermediate-temperature range. The behavior of hole mobility suggests a polaron conduction mechanism. Doping with aluminum has a weak influence on the mobility level, while the incorporation of Cr and Ti cations into the ferrite lattice decreases hole mobility up to four times.

The content of oxygen, electrical conductivity, and thermal electromotive force were measured for ferrite Sr3Fe2O6+δ over the oxygen partial pressure range 10−4–0.5 atm at 650–950°C. The partial molar thermodynamic functions of weakly bound oxygen in the oxide structure were determined. Labile oxygen ions were characterized as an ensemble of weakly interacting particles. The predominant charge carriers under experimental conditions were electron holes. An analysis of conductivity was performed using the data on the oxygen content. The concentration, activation energy, and mobility of charge carriers were determined. The results can be satisfactorily interpreted using the polaron transfer model of conductivity taking into account the charge disproportionation reaction for iron ions, 2Fe4+ = Fe3+ + Fe5+.

The oxygen content of the double cobaltite PrBaCo2O5 + δ was determined by coulometric titration in broad temperature and oxygen pressure ranges, and the partial thermodynamic functions of oxygen were evaluated. The results on the nonstoichiometry and structural properties of PrBaCo2O5 + δ demonstrate that, at 5 + δ < 5.3, this cobaltite has a high-temperature phase with lattice parameters a = 11.774 A, b = 11.932 A, and c = 7.609 A. The composition dependences of $$\Delta \bar H(O)$$ and $$\Delta \bar S(O)$$ indicate that the 3a p × 3a p × 2a p orthorhombic structure persists in the range 5.15 ≤ 5 + δ ≤ 5.30. Some of the Co3+ ions are shown to disproportionate according to the scheme 2Co3+=Co2++Co4+.

Magnetic susceptibility, χ ( T ) , is investigated in ceramic La 1− x Ba x MnO 3 (LBMO) with x = 0.02 – 0.25 in the range of fields B = 10 – 80 G and temperatures T = 5 – 310 K . All samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition with T C increasing with x from 177 K ( x = 0.02 ) to 295 K ( x = 0.25 ) and magnetic irreversibility decreasing below T C with increasing x . In the PM phase an interval of the Curie–Weiss behavior of χ ( T ) with an effective Bohr magneton number, p eff ∼ 30 – 40 , is observed above T 1 ∼ 260 – 290 K . Below T 1 and down to T cr ∼ 190 – 220 K the susceptibility follows the scaling law χ - 1 ( T ) - χ - 1 ( T C ) ∼ ( T / T C - 1 ) γ with γ = γ 1 ≈ 1.4 corresponding to a three-dimensional (3D) Heisenberg spin system. Below T cr , χ ( T ) obeys the same scaling law as for T > T cr , but with another value of γ = γ 2 ≈ 1.7 – 1.8 , characteristic of a 3D percolation system. The temperature dependence of the susceptibility observed in the PM phase is explained by small FM particles embedded in the host LBMO matrix above T 1 . The size of these particles increases between T 1 and T cr up to nanometer scale, forming critical percolation clusters below T cr . The magnetic irreversibility is connected to a mixed, FM and cluster-glass, phase.

The resistivity, ?, of ceramic La1?xBaxMnO3 with x = 0.02?0.10 corresponding to the concentrations of holes c?0.15?0.17 displays an activated behaviour both above and below the paramagnetic to ferromagnetic transition temperature TC = 175?209?K, obtained from measurements of the magnetization. Above T~310?390?K ?(T,x) is determined by nearest-neighbour hopping of small polarons with activation energy Ea = 0.20?0.22?eV. Below the onset temperature Tv = 250?280?K, depending on x, a Shklovskii?Efros-like variable-range hopping conductivity mechanism, governed by a soft temperature independent Coulomb gap, ??0.44?0.46?eV, and a rigid gap, ?(T), is found. For the range T~50?120?K, ?(T) is connected to the formation of small lattice polarons in conditions of strong electron?phonon interaction and lattice disorder. The rigid gap obeys a law ?(T)~T1/2 within two temperature intervals above and below TC, exhibits an inflection at TC and reaches at Tv a value of ?v?0.14?0.18?eV. Such behaviour suggests a spin dependent contribution to ?(T). The localization radius of the charge carriers, a, has different constant values within the temperature intervals where ?(T)~T1/2. With further decrease of T, a increases according to the law expected for small lattice polarons.

In order to identify the effects of minor titania additions and La:Sr cation ratio on the properties of lanthanum-strontium ferrites with high ionic conductivity, selected compositions in the La 1− x Sr x Fe 1− y Ti y O 3− δ system ( x = 0.5 and 0.7; y = 0 – 0.25 ) have been appraised employing dilatometry, oxygen permeation studies and total conductivity with Seebeck coefficient measurements in the oxygen partial pressure ( p (O 2 )) range, 10 −20 to 0.5 atm. The total conductivity is predominantly p -type electronic in the p (O 2 ) range 10 −8 –0.5 atm, with a relatively low, temperature-activated hole mobility indicating a hopping mechanism. Oxygen-ionic and n -type electronic transport is dominant for oxygen partial pressures below 10 −14 –10 −10 atm. Titanium addition lowers electronic and oxygen ionic conductivity in both regimes, but also substantially decreases thermal expansion coefficients (TECs). The average TEC values are ( 12.4 – 13.6 ) × 10 −6 K −1 at 300–900 K and ( 21.6 – 24.9 ) × 10 −6 K −1 at 900–1300 K in air. In oxidizing atmospheres the steady-state oxygen permeation fluxes through La 1− x Sr x FeO 3− δ ( x = 0.5 – 0.7 ) are similar, whereas under reducing conditions, La 0.5 Sr 0.5 FeO 3− δ exhibits the highest ionic conductivity, rendering this composition a most promising parent compound for mixed-conducting membranes operating under large p (O 2 ) gradients. The activation energies for ionic transport at low p (O 2 ), 68–75 kJ/mol, are essentially independent of dopant concentration.

Ceramic samples of LaSr2Fe3-yCryO8+δ (y = 0, 0.3, 0.6, and 1.0) were characterized with X-ray powder diffraction, thermal gravimetry, dilatometry, and total conductivity measurements in the temperature range 750−950 °C at oxygen partial pressures between 10-22 and 0.5 atm. When prepared in air, the doped ferrites adopt rhombohedral R3c structure. The loss of oxygen from the crystal lattice results in formation of the vacancy-ordered orthorhombic structure LaSr2Fe3O8 for the parent ferrite at temperatures above 750 °C and oxygen pressures below about 10-5 atm while chromium substituted samples retain the rhombohedral structure. The isothermal ion conductivity is found to decrease with the increase in chromium doping from y = 0 to y = 0.6. However, an increase in the chromium content to y = 1 results in an increase in the oxygen ion conductivity to about 0.2 S/cm. This behavior is explained with a model where the oxygen ions coordinated to chromium are not excluded entirely from the transport mechanism.

The total electrical conductivity of strontium ferrites, including intergrowth Sr4Fe6O13+δ, Sr3Fe2O6+δ with a Ruddlesden–Popper structure, and SrFeO2.5+δ where the cubic perovskite lattice transforms into vacancy-ordered brownmillerite at p(O2)

Substitution of iron with aluminum in perovskite-type La 0.3 Sr 0.7 Fe 1− x Al x O 3− δ ( x =0–0.4) decreases the unit cell volume, thermal expansion, and partial oxygen ionic and electronic conductivities. At oxygen partial pressures from 10 −10 –10 −8 to 0.5 atm, the total conductivity is predominantly p -type electronic. Temperature-activated character and relatively low values of hole mobility, estimated from the total conductivity and Seebeck coefficient data, suggest a small polaron mechanism. The oxygen ion transference numbers of La 0.3 Sr 0.7 Fe 1− x Al x O 3− δ ( x =0.2–0.4) in air, determined by the faradaic efficiency measurements, vary from 7×10 −4 to 1×10 −2 at 1023–1223 K, increasing with temperature and aluminum content. As for other (La,Sr)FeO 3 -based phases, reducing oxygen pressure below 10 −14 –10 −10 atm results in dominating ionic and n -type electronic contributions to the total conductivity. The activation energies for ionic transport in La 0.3 Sr 0.7 (Fe,Al)O 3− δ , 95–102 kJ mol −1 , are essentially independent on the cation composition and oxygen chemical potential, while the ionic conductivity may slightly increase on reducing p (O 2 ). The level of oxygen ionic conduction in Al-containing ferrites was found lower than in Ga-substituted analogues. The average thermal expansion coefficients of La 0.3 Sr 0.7 Fe 1− x Al x O 3− δ ceramics, calculated from dilatometric data in air, are the in range (12.1–12.9)×10 −6 K −1 at 350–700 K and increase up to (23.2–27.4)×10 −6 K −1 at 700–1300 K.

Thermopower and conductivity are measured for the perovskite-like manganite La1−xBaxMnO3 (0.02⩽x⩽0.35) in the temperature range 200–950°C and oxygen pressure varying between 10−11 and 0.5 atm. The data for thermopower and electrical conductivity indicate a transport mechanism dominated by adiabatic hopes of small polarons. The high-temperature limit for the thermopower is mainly defined by the spin contribution while configurational contribution does not depend essentially on the doping level. Changes in the conductivity with doping are shown to reflect variations in the mobility of charge carriers.

The electrical properties of perovskite-related oxide La0.3Sr0.7Fe1 - xGaxO3 − δ (x = 0–0.5) are reported within the temperature range 750 to 950 °C and the oxygen partial pressure range between 10−19 and 0.5 atm. The maximum solid solubility of gallium in the iron sublattice of La0.3Sr0.7FeO3 − δ is close to 30%. At oxygen pressures about 10−4 atm, the materials undergo a transition from perovskite to oxygen vacancy ordered structures. The type of vacancy ordering depends on gallium content. Both p- and n-type electronic conductivities decrease when insulating gallium cations having stable oxidation state are incorporated into the iron sublattice of the ferrite. The observed temperature and oxygen pressure dependencies of the p-type electronic conductivity in the ordered phases suggest a transition from the intrinsic regime, when the electron–hole conduction is governed by the band gap, to the extrinsic regime, controlled by the amount of the oxygen excess in the vacancy ordered structure. The ordered strontium–lanthanum ferrite was shown to be a mixed conductor with oxygen ionic conductivity of about 0.1 S cm−1 at 900 °C. Ionic conduction in the vacancy ordered phases decreases with increasing gallium concentration.

The crystal structure of YBa2Cu3−xCoxO6+δ solid solutions, where x = 0.2, 0.4, 0.6, and 0.8, was studied by powder neutron diffraction. The charged states of the cations were calculated using the interatomic distances obtained in neutron diffraction measurements. It is shown that cobalt in the Cul position has valence 3+ and octahedral environment for x = 0.2 and 0.4. As x increases, the valence of some cobalt ions in the above positions changes to 4+, the environment changes to tetrahedral, and copper in the Cu2 position is partly substituted. Cobalt in the Cu2 positions has valence 2+ and does not change the square pyramidal arrangement of oxygen ions surrounding this position.

The equilibrium oxygen content of YBa2Cu3-xCoxO6+δ (0.2 ≤x ≤ 0.8) solid solutions was determined by coulometric titration at temperatures in the range 600–850°C and oxygen pressures 1 ≤po 2 ≤ 105 Pa. The partial enthalpy and entropy of oxygen dissolution were evaluated as a function of composition. The thermodynamic functions were found to change sharply near the high- and low-oxygen limits of the solid solution. The results are interpreted in terms of a quasi-chemical model considering three inequivalent oxygen sites in the basal plane.