The A-site nonstoichiometry in doped ABO3 perovskites is typically introduced to tailor the materials' functional properties through defect engineering and to promote dopant exsolution. In this work, the redox behavior and electrical properties of 5 mol % Sr-deficient strontium titanate doped with the first-row d-block elements (Mn, Fe, Co, Ni) were investigated to elucidate the relationships between dopant characteristics and the resulting properties of the final materials. The materials were sintered at 1200 °C and 1400 °C to obtain samples with significantly different microstructures. The results indicate that although the B-O bond energy contributes to the overall physicochemical behavior of the investigated materials, the properties of SrTiO3-based systems are generally shaped by the nature of the dopant and, more specifically, by its intrinsic characteristics. In Fe- and Ni-doped materials, the key factor is the ability of these cations to be exsolved as metallic particles under reducing conditions. In Co-containing materials, the physicochemical behavior is strongly affected by the volatility of cobalt species at high temperatures. In contrast, Mn-doped systems are mainly influenced by temperature-dependent site preferences of Mn ions, which can occupy both the Sr and Ti sublattices.

In this work, a group of mixed ionic-electronic conductors, SrFe1-xCoxO3-delta (x = 0, 0.4, 0.6, 0.8), synthesised with NiO as a sintering aid was studied. The total electrical conductivity as a function of temperature was analysed using the DC-4W method. All investigated materials exhibited a maximum conductivity at temperatures between 620 and 870 K. Thermally activated conduction below- and metal-like conductivity behaviour above the maximum temperature was observed. Seebeck coefficient measurements of SrFe1-xCoxO3-delta (x = 0, 0.4, 0.6, 0.8) showed that all materials exhibited a p-type electronic conductivity in air. Furthermore, thermoelectric studies have enabled the determination of temperature dependencies of electron hole concentration and their mobility. With higher Co content in the materials, the Seebeck coefficient was lower, while the concentration of electron holes increased. With increasing temperature, the concentration of electron holes declined in all materials due to thermal reduction.

In this study, compositionally complex cobaltites with the general formula BaLnCo2O6−δ with three to eight different lanthanides at the Ln-site were synthesized using the solid-state reaction method and studied. Analysis of entropy metrics and configurational entropy calculations indicated that these compounds are medium entropy oxides. All of these crystallize as tetragonal double perovskites from the space group P4/mmm. The unit cell parameters are controlled by the average ionic radius, not the configurational entropy. On the other hand, the oxygen non-stoichiometry is consistently higher than in the case of low entropy double perovskite cobaltites. The total electrical conductivity of all materials in studied conditions is well above 50 S/cm, peaking at 1487 S/cm for BaLa1/3Nd1/3Gd1/3Co2O6−δ at 300°C. The electrical conductivity decreases with the number of substituents.

In this work, exsolution is achieved from both the A-site and B-site of (BaGd0.8La0.2)1-xAgxCo2O6-delta and (BaLa)1-xAgxCoFeO6-delta (x = 0.04, 0.1, and 0.2) perovskites prepared via solid-state sintering. Through synchrotron radiation powder X-ray diffraction and X-ray absorption spectroscopy techniques, the chemical composition of the nanoparticles was determined to constitute both Ag and CoO. Microstructural studies were done using scanning electron microscopy with varying sizes and shapes of nanoparticles present for respective annealing atmospheres and temperatures. By applying a numerical model to experimental data, it was also established that the changes in enthalpy for oxygen vacancy formation decrease with an increase in silver dopant. From thermogravimetric measurements, the single (BaLa)0.95Ag0.10CoFeO6-delta perovskite had relatively higher water uptake than the layered (BaGd0.8La0.2)0.95Ag0.10Co2O6-delta perovskite. The total electrical conductivity done in dry and wet conditions decreased with an increase in temperature in the range of 300-800 degrees C for both layered and single perovskites. The results obtained from electrical conductivity relaxation measurements of (BaGd0.8La0.2)0.95Ag0.10Co2O6-delta with nanoparticles exhibit increased oxygen reduction reaction activity than (BaLa)0.95Ag0.10CoFeO6-delta with nanoparticles.

In this paper, we present the analysis of the influence of nonstoichiometry on the properties of polycrystalline (Y0.07Sr0.93)xTi0.8Fe0.2O3-s compounds for x = 0.92; 0.96; 1.00; 1.06, and 1.08. The crystal structure, microstructure, and electrical conductivity of the samples were characterized. Structural studies showed that the samples exhibited a cubic perovskite structure, both in the case of strontium excess and deficiency. The unit cell parameters varied with the level of (Y,Sr) nonstoichiometry, increasing from 3.8984(1) angstrom to 3.9145(1) angstrom with increasing x. Microstructure studies showed that the stoichiometric and strontium-deficient samples were dense, while the strontium excess affected higher porosity. The average grain size in the tested ceramics was between (1.5 +/- 0.2) mu m and (4.0 +/- 0.4) mu m, while the agglomeration ratio for all compounds was between 6 and 17. All compositions showed thermally-activated electrical conductivity, which was significantly reduced upon introducing (Y,Sr)-site nonstoichiometry and excess. Depending on the composition, studied materials showed a total electrical conductivity of 10-4 to 10-1 S cm-1 at 450-850 degrees C range. Samples with a (Y,Sr)-site deficiency exhibited activation energies for the conduction process of 0.37-0.41 eV, while those with excess strontium showed lower conduction activation energies of 0.26-0.28 eV. The structural and electrical properties of the materials were discussed in terms of the defect chemistry based on antisite defects. The results strongly contradict most of the literature reports on Sr-site nonstoichiometric SrTiO3, showing the significant impact of the Fe3+ substituent in the B-site on the structure and charge transport.

Multicomponent oxides often have exceptional thermal stability and interesting electronic properties. The present work presents the thermoelectric and electrical properties of the Ba(Zr0.2Hf0.2Sn0.2Ti0.2Fe0.2)O3-delta and Ba(Zr0.1Hf0.1Sn0.1Ti0.1Co0.1Ce0.1Bi0.1Fe0.1Y0.1Zn0.1)O3-delta multicomponent perovskites. Single-phase cubic perovskites were synthesized using the solid-state reaction method. They were characterized using X-ray diffraction, drop-solution calorimetry, and thermogravimetry methods. The total electrical conductivity and Seebeck coefficient measurements were performed in dry and wet air at temperatures between 600 and 1050 K. It was found that Ba(Zr0.1Hf0.1Sn0.1Ti0.1Co0.1Ce0.1Bi0.1Fe0.1Y0.1Zn0.1)O3-delta is thermodynamically less stable than Ba(Zr0.2Hf0.2Sn0.2Ti0.2Fe0.2)O3-delta. Moreover, this oxide incorporates a higher amount of water and exhibits higher conductivity and lower Seebeck coefficient. Charge transport in both perovskites can be assigned to the small-polaron hopping process via electron holes. An interesting temperature dependence of the Seebeck coefficient was found and, at temperatures above 750 K, related to hopping between energetically inequivalent states.

In this work, the oxygen nonstoichiometry and local structural features of the SrFe1-x Co x O3-delta (x = 0, 0.2, 0.4, 0.6, 0.8) system, which are mixed ionic-electronic conducting (MIEC) perovskite oxides, were systematically investigated. All synthesized materials exhibited a pseudocubic crystal structure, as confirmed by X-ray diffraction (XRD). Oxygen nonstoichiometry (delta) was determined using iodometric titration and X-ray absorption spectroscopy (XAS) at the Fe and Co K-edges. An increase in oxygen nonstoichiometry was observed with an increasing cobalt content. XAS analysis at the transition metal (TM) K-edges enabled the independent determination of average oxidation states for Fe and Co, revealing Fe to be approximately 3.2+ and Co in the range of 2.9+ to 3.0+. Furthermore, local coordination environments around transition metal ions were predominantly octahedral, supporting the results obtained via XRD. Complementary K-edge XAS measurements provided insights into the spin states of B-site cations, indicating a mixed- and an intermediate-spin state near the surface and a high-spin state in the bulk of the materials. The surface XAS measurements at the L-edge of cobalt confirmed the presence of Co2+ species. The combined high oxygen deficiency, dominant octahedral coordination, and high structural symmetry suggest the absence of long-range vacancy ordering in the SrFe1-x Co x O3-delta materials. Furthermore, they were preferentially located around cobalt ions.

The study shows the effects of introduction of multiple lanthanides into a single lattice site in a series of Ba Ln"1 x Ln"1 x Ln"1 x ...Lnx"1 x Co2O6_delta. The X-ray diffraction and transmission electron microscopy confirmed that up to 12 lanthanides can be successfully introduced into the material, and as a result, a tetragonal double perovskite structure is formed. Co mixed 3+/4+ valence state has been confirmed independently by iodometric titration and X-ray Absorption Spectroscopy. The effect of multiple elements' presence on the local environment of Co has been evaluated by employing Extended X-ray Absorption Fine Structure analysis. All materials are ptype conductors with total conductivity above 1000 S.cm_ 1 at 300 degrees C and small positive Seebeck coefficients of about 1-23 mu V.K_1. The electrical conductivity of multicomponent compounds is higher than for most double perovskite cobaltites.

In this work, the chosen physicochemical properties of single-phase multicomponent oxides BaTi1/8Fe1/8Co1/8Y1/8Zr1/8Sn1/8Ce1/8Hf1/8O3-delta and BaTi1/9Fe1/9Co1/9Y1/9Zr1/9Sn1/9Ce1/9 Hf1/9Bi1/9O3-delta were studied. The microstructure of the compounds strongly depended on the presence of bismuth in the structure. The electrical transport studies showed a level of electrical conductivity of similar to 10(-3) - 10(-2) S/cm in the temperature range 673-1073 K. Electrical conductivity was thermally activated and the dominant conduction mechanism was the hopping of small polarons. Moreover, total electrical conductivity changes in the dry and humidified atmosphere at lower temperatures due to the presence of protonic defects in the structure. Thermoelectric measurements showed a relatively high value of the Seebeck coefficient for studied ceramics. Its values ranged between 50 and 250 mu V/K depending on the sample and temperature. The Seebeck coefficient sign was positive, meaning that electron holes and/or oxygen vacancies were predominant charge carriers in oxidizing atmospheres. Additionally, the Seebeck coefficient was found to be different in the humidified atmosphere which indicates an influence of protonic defects on thermoelectric transport. The obtained power factor P-f turned out to be low and dependent on the presence of protonic defects in the structure. This indicates, that the efficiency of the MOs-based operating thermoelectric generators can be controlled by changing the partial pressure of water vapor.

An essential prerequisite for an efficient solid oxide fuel cell (SOFC) at intermediate temperatures is the advancement of cathode materials that exhibit a heightened oxygen reduction reaction (ORR) rate coupled with a well-suited microstructure. In this study, we have undertaken the design and synthesis of Nd-substituted La0.6Sr0.4Co0.2Fe0.8O3-s (LSCF) nanofibrous cathodes through a cost-effective electrospinning technique. The electrocatalytic performances of the resulting La0.6-xNdxSr0.4Co0.2Fe0.8O3-s (LNSCF) nanofiber cathodes are systematically evaluated and compared with that of the pristine LSCF cathode. The results reveal that an optimal level of Nd substitution significantly enhances the electrochemical performance of the LSCF cathode. The polarization resistance values, assessed at 800 degrees C, for LNSCF nanofibrous mesh cathodes with x = 0, 0.1, 0.2, and 0.3, are found to be 0.06, 0.03, 0.04, and 0.05 Omega center dot cm2, respectively. Moreover, the anode-supported single cell, utilizing the La0.5Nd0.1Sr0.4Co0.2Fe0.8O3-s nanofiber cathode, achieves a maximum power density of 579 mW/ cm2 at 800 degrees C, which is significantly higher than that of unsubstituted LSCF nanofiber cathode 403 mW/cm2. This improvement can be attributed to a balanced trade-off among enhanced catalytic activity, reduced electrical conductivity, and minimized thermal expansion coefficient mismatch between the cathode and the underlying interlayer. These findings illustrate that an appropriate Nd substitution at the A-site of LSCF serves as an effective strategy for enhancing the performance of proton-conducting SOFCs.

In this report, the high-temperature transport properties of (Dy1−xCax)(Zr0.2Hf0.2Sn0.2Ti0.2Ge0.2)O7 pyrochlore oxides with x = 0, 0.05, and 0.1 are studied in dry and humid air. The phase composition and crystal structure were determined by using x-ray and neutron diffraction. The addition of calcium to the structure caused an increase in the concentration of oxygen vacancies, indicating an ionic charge compensation mechanism. Electrical studies allowed us to determine the total electrical conductivity as a function of the synthesis atmosphere and pH2O. The electrical conductivity turned out to be at the level of ∼10−3 S/cm at 800 °C, and only a slight effect of the presence of protonic defects in the structure on the total electrical conductivity was observed. In general, the samples had a low electrical conductivity with a relatively high activation energy of conduction.

In this work, partial protonic conductivity in mixed conducting (BZCY721) and BaGd0.3La0.7Co2O6-delta (BGLC137) was studied. For this purpose, a modified DC Hebb-Wagner polarization method was used. A four-wire type of galvanic cell as well as a suitable calculation model was applied. The method was validated using proton conducting electrolyte - BaZr0.7Ce0.2Y0.1O3-delta - as a reference material. For the first time, protonic partial conductivity in BaGd0.3La0.7Co2O6-delta was determined. It was found that at 600 degree celsius its total conductivity was similar to 550 S cm(-1), whereas the partial protonic conductivity under the same conditions was 4.4 x 10(-5) S cm(-1) (protonic transference number of 7.6 x 10(-8)). Therefore, the proposed measurement cell and the applied model allowed for the determination of a minor protonic conductivity in the BGLC137 electronic conductor.

The electrical properties of the entropy stabilized oxides: Zr6Nb2O17, Zr6Ta2O17, Hf6Nb2O17 and Hf6Ta2O17 were characterized. The results and the electrical properties of the products (i.e. ZrO2, HfO2, Nb2O5 and Ta2O5) led us to hypothesize the A(6)B(2)O(17) family is a series of mixed ionic-electronic conductors. Conductivity measurements in varying oxygen partial pressure were performed on A(6)Nb(2)O(17) and A(6)Ta(2)O(17). The results indicate that electrons are involved in conduction in A(6)Nb(2)O(17) while holes play a role in conduction of A(6)Ta(2)O(17). Between 900 C-degrees-950 C-degrees, the charge transport in the A(6)B(2)O(17) system increases in Ar atmosphere. A combination of DTA/DSC and in situ high temperature X-ray diffraction was performed to identify a potential mechanism for this increase. In-situ high temperature X-ray diffraction in Ar does not show any phase transformation. Based on this, it is hypothesized that a change in the oxygen sub-lattice is the cause for the shift in high temperature conduction above 900 C-degrees-950 C-degrees. This could be: (i) Nb(Ta)(4+)- oxygen vacancy associate formation/dissociation, (ii) formation of oxygen/oxygen vacancy complexes (iii) ordering/disordering of oxygen vacancies and/or (iv) oxygen-based superstructure commensurate or incommensurate transitions. In-situ high temperature neutron diffraction up to 1050 C-degrees is required to help elucidate the origins of this large increase in conductivity.

In this work, the oxidation properties of austenitic 316L stainless steel powder and sintered porous support were investigated at the temperature range of similar to 600-750 degrees C for 100 hours in ambient air. Oxidation kinetics was determined by continuous thermogravimetry and analyzed employing parabolic rate law. It was observed that oxidation leads to the formation of an oxide scale, with substantial oxidation occurring at >= 650 degrees C in the powder. The porous steel support was fabricated using the tape casting method with two distinct pore former concentrations. The micro-structural features of both the powder and support were investigated by X-ray diffractometry and scanning electron microscopy coupled with energy-dispersive X-ray analysis. The mechanical properties of the metal support were examined before and after oxidation via a microhardness test. The effect of porosity on the resulting properties of the metal support was also highlighted. In summary, 316L stainless steel support suits SOCs applications below 600 degrees C.

Higher iron content in BaCe 0.6 Zr 0.2 Y 0.2− x Fe x O 3− δ system leads to decreased oxygen vacancy concentration and diminished proton uptake, as well as lower electronic and oxygen ionic conductivity.

This work presents the results of a comprehensive study on the impact of the A-site non-stoichiometry of SrxTi0.3Fe0.7O3-δ (x=0.90, 0.95, 1.00, 1.05) ceramics on their physicochemical properties. The materials were fabricated by the conventional solid-state reaction method and their structure was determined by X-ray diffractometry, X-ray photoelectron spectroscopy and electron microscopy. Their sintering and thermal expansion properties were then evaluated. The electrical properties of the materials were determined by electrical conductivity and electrical relaxation measurements (on bulk materials) and by electrochemical impedance spectroscopy (EIS) studies of symmetrical, CGO-electrolyte based, porous electrodes. Finally, fuel cell tests with the non-stoichiometric electrodes were evaluated. To elucidate the electrochemical reaction pathways for oxygen reduction/evolution reaction, EIS measurements were carried out in different pO2 and were analysed via the distribution of relaxation times method. The results showed a dependence of materials’ properties on the A-site non-stoichiometry, which can be used to fine-tune their properties, e.g. increase the surface exchange rate or decrease the thermal expansion coefficient.

This work presents the results of research on the transportproperties of the high - entropy BaZr1/8Hf1/8Sn1/8Ti1/8Y1/8In1/8Sm1/8Yb1/8O3- x perovskite oxide with special focus on proton transport. The presented study is part of broader work in which we focus on multiple different chemical compositions with the cation number varying from 5 up to 12 (in B-sublattice). The presence of proton defects is analyzed with thermogravimetry, whereas the results of electrochemical impedance spectroscopy in dry, H2O-, and D2O-containing synthetic air in the 300-800 degrees C temperature range enable the evaluation of the proton and deuterium conductivities. The isotope effect is observed and discussed. The obtained data allow us to establish the contribution of proton conductivity to the total one and the transport numbers for proton/deuterium conductivity. Based on the bulk and grain boundary conductivities, the potential at a grain boundary f0, Debye length LD, and space-charge layer (SCL) thickness. for proton defects is calculated. The potential barrier heights were found to be significantly lower than those observed for typical polycrystalline-doped barium zirconates. For the first time in the case of high-entropy oxides, the electrical conductivity relaxation (ECR) studies are performed, allowing the calculation of water kinetic coefficients. The ECR in the 300-600 degrees C temperature range revealed a single-fold nature, which indicates a negligible component of the electronic hole conductivity in the hydrated material. The chemical diffusion coefficient of water DOH and the chemical surface exchange coefficient of water kOH along with their activation energies are determined. The chemical diffusion coefficient DOH is in a range of 10(1)(-8)-10(1)(-6) cm2 s(-1), and the chemical surface exchange coefficient kOH is in a range of 10(1)(-6)-10(1)(-4) cm s(-1).

This work investigates how configurational entropy in oxides could affect proton conductivity. For this purpose, three samples of different elemental compositions are synthesized. Five, six and seven elements were introduced into the A-site of ANbO4, forming La1/5 Nd1/5 Sm1/5Gd1/5 Eu1/5NbO4, La1/6Nd1/6Sm1/6Gd1/6Eu1/6Ho1/6NbO4 and La1/7Nd1/7Sm1/7Gd1/7Eu1/7Ho1/7Er1/7NbO4, respectively. The high configuration disorder changes the local environment, which can have a notable effect on many properties, including proton transport, which is the focus of this work. The conductivity was measured in different atmospheres; dry and wet and in a different temperature range (600-800 °C) to compare the proton transport as well as study the effect of temperature. A homogenous single-phase monoclinic fergusonite was obtained for the three samples. Proton conductivity, measured by means of comparing the conductivity in dry and wet atmospheres, was observed in all samples. La1/5 Nd1/5 Sm1/5Gd1/5 Eu1/5NbO4 exhibited the highest conductivity, about 3.0 × 10-6 S cm-1 at 800 °C in the wet atmosphere, while in the dry atmosphere it was about 2.2 × 10-6 S cm-1 at the same temperature, which implies a modest proton conductivity in this class of materials.