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In this work, characterization of BaSn 0.5 In 0.5 O 2.75 , Ba 0.9 La 0.1 Sn 0.5 In 0.5 O 2.8 and Ba 0.9 Gd 0.1 Sn 0.5 In 0.5 O 2.8 perovskite-type oxides is reported concerning crystal structure, presence of protons in hydrated samples and transport properties of dense pellets in dry and wet atmospheres at elevated temperatures. Compounds possess cubic structure at room temperature, which is in accordance with Goldschmidt's tolerance factor t being close to 1. Introduction of smaller Ln partially substituting Ba results in a decreased unit cell volume. Upon hydration in wet air unit cell of the materials enlarge, with magnitude of the effect correlated with chemical composition. High temperature X-ray measurements in synthetic air revealed release of water from hydrated materials occurring above 200 °C, and associated non-monotonous dependence of the respective unit cell parameter. No significant influence of dopants is found concerning thermal expansion of the studied oxides. Performed thermogravimetric measurements on hydrated and dried samples with supplementary mass spectroscopy analysis are in agreement with structural results, confirming presence of water in the hydrated compounds, but also show CO 2 release during heating. Electrochemical impedance measurements, conducted for densified pellets in dry, H 2 O- and D 2 O-containing synthetic air, indicate an appearance of proton conductivity, with different dependence of bulk and grain boundary components on chemical composition. Supplementary electrical conductivity relaxation experiments, which allowed calculating diffusion and surface coefficients are also provided. [ABSTRACT FROM AUTHOR]

La 2 Ni 0.5 Cu 0.5 O 4 and Pr 2 Ni 0.5 Cu 0.5 O 4 Ruddlesden-Popper-type oxides were synthesized by a soft chemistry method and characterized in terms of their crystal structure as a function of temperature, thermal expansion coefficient, oxygen content, transport properties and chemical stability, as well as compatibility in relation to Ce 0.8 Gd 0.2 O 1.9 electrolyte. La 2 Ni 0.5 Cu 0.5 O 4 crystallizes in F 4/ mmm space group, while Pr 2 Ni 0.5 Cu 0.5 O 4 possesses Bmab symmetry. Oxygen nonstoichiometry was determined, showing oxygen excess at room temperature: La 2 Ni 0.5 Cu 0.5 O 4.12 and Pr 2 Ni 0.5 Cu 0.5 O 4.07 , but with only small changes in air up to 850 °C. The obtained TECs are compatible to most commonly used electrolytes. Pr 2 Ni 0.5 Cu 0.5 O 4 possesses relatively good electrical conductivity, exceeding 100 S cm −1 in 300–800 °C. A maximum on the electrical conductivity, present for both materials, correlates well with minimum, observed on Seebeck coefficient characteristics. For Pr 2 Ni 0.5 Cu 0.5 O 4 -based SOFC, maximum power densities exceeding 0.13 W cm −2 at 800 °C were recorded. Despite good performance, stability issues arise from a partial decomposition of the materials at 1000 °C. [ABSTRACT FROM AUTHOR]

In this work, W-containing Sr 1 − x Ba x Fe 0.75 W 0.25 O 3 − δ ( x = 0, 0.5, 1) perovskite-related oxides have been for the first time evaluated in terms of their possible application as anode materials in solid oxide fuel cells. Crystal structure, thermal expansion coefficient, transport properties, oxygen content, chemical compatibility in relation to ceria-based electrolyte, and stability of the materials in reducing atmospheres have been studied. It was found that SrFe 0.75 W 0.25 O 3 − δ and Sr 0.5 Ba 0.5 Fe 0.75 W 0.25 O 3 − δ oxides show simple perovskite-type structure with cubic Pm - 3m symmetry, while BaFe 0.75 W 0.25 O 3 − δ exhibits hexagonal P 6 3 / mmc structure. Small grains (~ 2 μm) can be obtained for SrFe 0.75 W 0.25 O 3 − δ compound with very simple, high-temperature synthesis process in air. Large oxygen nonstoichiometry changes of Δ δ ≈ 0.36 were observed for SrFe 0.75 W 0.25 O 3 − δ oxide upon heating in 5 vol.% H 2 in argon. Seebeck coefficient and electrical conductivity measurements revealed that SrFe 0.75 W 0.25 O 3 − δ oxide exhibits p -type conductivity in air and n -type conductivity under reducing conditions. This oxide presents relatively good chemical compatibility in relation to Ce 0.8 Gd 0.2 O 1.9 electrolyte, and chemical stability in 5 vol.% H 2 in argon up to at least 800 °C. Electrochemical impedance spectroscopy studies for SrFe 0.75 W 0.25 O 3 − δ -based cells conducted in pure hydrogen and CH 4 indicated the possibility of the application of SrFe 0.75 W 0.25 O 3 − δ as the anode material in SOFCs. [ABSTRACT FROM AUTHOR]

Results of studies of crystal structure (XRD method with Rietveld analysis), as well as transport properties (AC impedance method in dry and wet Ar atmospheres) are presented in this work for oxygen vacancy-disordered Ba 1 − x La x (In,Zr,Sn)O 3 − δ with δ = 0.375. La doping in the A-site, as well as Zr or Sn doping in the B-site resulted in stabilization of the cubic Pm –3 m perovskite structure for all of the considered materials, despite having high In-content. Systematic studies of the electrical conductivity, performed in the 300–850 °C temperature range, allowed discussing the relationship between proton conductivity and structural parameters in the studied compounds. It was found that materials with a larger unit cell parameter possess higher proton conductivity in the whole temperature range, and, at the same time, the proton transference number for these compounds remains higher at higher temperatures. [ABSTRACT FROM AUTHOR]

In this paper we report on crystal structure and oxygen storage properties of A-site cation ordered BaLnMn 2 O 5+δ (Ln: Pr, Nd, Sm, Gd, Dy, Er and Y) perovskite-type oxides. The materials show practically complete and reversible change between fully reduced BaLnMn 2 O 5 and oxidized BaLnMn 2 O 6 , which occurs at moderate temperatures (300–500 °C) during changes of the oxygen partial pressure (air, 5 vol.% H 2 in Ar). Based on the thermogravimetric measurements, reversible oxygen storage capacity, characteristic temperature of oxidation and reduction, as well as kinetics of these processes are given. Structural characterization was performed at room temperature for the reduced and oxidized materials by Rietveld analysis of the XRD data. These results are accompanied by in situ high temperature XRD measurements of the oxidation process, performed for BaNdMn 2 O 5 in air. [ABSTRACT FROM AUTHOR]

B-site rock salt-type ordered Sr 2 MMoO 6 (M = Mg, Mn, Fe, Co, Ni) oxides have been systematically investigated in terms of their crystal structure, oxygen non-stoichiometry, transport properties, thermal expansion and chemical stability. Structural evolution on temperature of the studied materials was interpreted on a basis of octahedra rotation, with I 4/ m → Fm -3 m phase transition. In the case of P 2 1 / n → I 4/ m transformation recorded for Sr 2 MnMoO 6 , a region of coexistence of two phases was observed. The Fe-containing compound was found to possess very high electrical conductivity, around 1000 S cm −1 in 5 vol.% H 2 in Ar, and small negative Seebeck coefficient. Studies show that Mn- and Fe-containing compounds are stable only in reducing conditions, Co- and Ni-containing ones are stable only in oxidizing conditions, while Sr 2 MgMoO 6 remains stable in a wide range of oxygen partial pressures. Recorded power density of a button-type SOFC with Sr 2 FeMoO 6 -based anode was 0.32 W cm −2 at 900 °C. [ABSTRACT FROM AUTHOR]

Selected LnBa0.5Sr0.5Co1.5Fe0.5O5+δ (Ln - Pr, Nd, Sm, Gd and Y) oxides were studied in terms of their phase composition, formation of cation-ordered crystal structure, oxygen nonstoichiometry and transport properties. Despite partial substitution of bigger Ba2+ by smaller Sr2+ cations, A-site (Ln-Ba,Sr) cation ordering in LnBa0.5Sr0.5Co1.5Fe0.5O5+δ is preserved, but only for smaller Ln cations (Y3+, Gd3+). In the case of SmBa0.5Sr0.5Co1.5Fe0.5O5+δ, the synthesis procedure yielded material partially ordered, while for Pr3+ and Nd3+ cations XRD measurements indicated formation of cation-disordered samples. Oxygen content in the disordered materials is close to stoichiometric one (δ≈1) at room temperature, while for cation-ordered samples δ<1. Thermogravimetric measurements indicated that above 250°C a decrease of mass occurs for all of the studied materials. Except for Y-containing sample, larger mass loss at 800°C occurs for materials with heavier Ln element. The ordered materials show higher activation energy of the electrical conductivity in 25–300°C temperature range, as well as different temperature dependence of Seebeck coefficient, comparing to the disordered ones. The highest electrical conductivity was measured for PrBa0.5Sr0.5Co1.5Fe0.5O5+δ. For this compound the ionic conductivity at 800°C was determined to be of the order of 0.03Scm−1. [ABSTRACT FROM AUTHOR]

Abstract: Crystal structure and oxygen storage properties of A-site ordered BaY1− x Pr x Mn2O5+δ (x =0, 0.25, 0.5, 0.75 and 1) perovskite-type oxides are reported, showing almost complete and reversible change (Δδ>0.94mol mol−1) occurring between fully reduced BaY1− x Pr x Mn2O5 and oxidized BaY1− x Pr x Mn2O6 during reduction in 5vol.%H2 in Ar atmosphere and oxidation in air at 500°C. All reduced compounds, as well as oxidized ones for x ≥0.5 possess tetragonal structure with P4/nmm (or P4/mmm for BaPrMn2O6) symmetry at room temperature. In the case of BaY0.75Pr0.25Mn2O6 and BaYMn2O6, good Rietveld refinements of XRD data were obtained assuming either monoclinic P121 or triclinic P-1 symmetry. The oxidation process causes a significant decrease of unit cell volume, which is additionally linearly dependent on average ionic radius of Y1− x Pr x . Due to a higher molar mass, an increasing Pr content causes a decrease of reversible oxygen storage capacity; nevertheless, Pr-containing materials show improved reduction rate and oxidize at lower temperatures. The optimized BaY0.75Pr0.25Mn2O5-BaY0.75Pr0.25Mn2O6 system showed very stable performance for 50cycles. The obtained results indicate that by an appropriate chemical modification, it is possible to enhance oxygen storage-related properties of BaY1− x Ln x Mn2O5+δ (Ln — lanthanides) oxides, and such materials are promising for oxygen storage technology application. [Copyright &y& Elsevier]

In this paper we report on oxygen storage-related properties of selected Co- and Fe-containing perovskite-type oxides, and analyze their advantages and disadvantages in relation to the Mn-based, A-site ordered BaYMn2O5+δ system. In particular, the crystal structure of reduced and oxidized Ln0.5A′0.5Co0.5Fe0.5O3−δ (Ln: La, Sm; A′: Sr, Ba) and La0.6Sr0.4Co0.8Fe0.2O3−δ is given, results of in situ XRD observation of the oxidation process of the reduced materials is presented, as well as oxygen storage capacity and kinetics measured on oxidation/reduction cycles in isothermal and non-isothermal conditions are reported. Rietveld refinement of the crystal structure carried out for reduced compounds revealed the presence of brownmillerite-type phase for La0.6Sr0.4Co0.2Fe0.8O2.42, La0.5Sr0.5Co0.5Fe0.5O2.53 and Sm0.5Sr0.5Co0.5Fe0.5O2.53. Upon oxidation these materials transform to perovskite-type phase. On the contrary, La0.5Ba0.5Co0.5Fe0.5O3−δ and A-site cation ordered Sm0.5Ba0.5Co0.5Fe0.5O3−δ possess the same crystal structure in the reduced and oxidized forms. What's more is that the oxidation process causes a significant decrease of the unit cell volume for each studied compound. Rapid in situ XRD studies (1min scans), performed every 5°C during oxidation of the materials, allowed to observe ongoing structural changes. TG measurements revealed unusually low onset temperatures of oxidation, with reduced La0.5Sr0.5Co0.5Fe0.5O3−δ oxidizing at about 40°C. Isothermal oxidation/reduction cycles measured with changing of the atmosphere between air and 5vol.%H2 in Ar, performed in 400–600°C allowed to establish oxygen storage-related properties of the studied materials, and it was found that La0.5Sr0.5Co0.5Fe0.5O3−δ shows enhanced kinetics of the reduction process, while for La0.6Sr0.4Co0.8Fe0.2O3−δ the measured reversible oxygen storage capacity can exceed 4.2wt.%, well above that of the BaYMn2O5+δ system. While these results are very promising, the main drawback arises from a low stability of the considered Co- and Fe-containing oxides, especially in terms of their long-time performance. [ABSTRACT FROM AUTHOR]

In this paper, we report on a synthesis procedure, structural and electrical properties of BaErMn2O5 and BaErMn2O6, A-site double perovskites having layered arrangement of Ba and Er cations. These materials belong to a family of BaLnMn2O5+δ oxides, which up to now were successfully synthesized for Ln=Y and La–Ho lanthanides. Up to our knowledge, this is the first report on the successful synthesis of BaErMn2O5 and BaErMn2O6, yielding>95wt% of the considered compounds. Structural characterization of the materials is given at room temperature, together with in situ XRD studies, performed during oxidation of BaErMn2O5 in air, at elevated temperatures up to 500°C. A complex structural behavior was observed, with oxidation process of BaErMn2O5 occurring at around 300°C. The oxidized BaErMn2O6 shows a structural phase transition at about 225°C. Results of structural studies are supported by thermogravimetric measurements of the oxidation process, performed in air, as well as reduction process, preformed in 5vol% of H2 in Ar. Additionally, isothermal oxidation/reduction cycles were measured at 500°C, showing interesting properties of BaErMn2O5+δ, from a point of view of oxygen storage technology. Electrical conductivity of BaErMn2O5 is of the order of 10−4 Scm−1 at room temperature and shows activated character on temperature with activation energy E a =0.30(1) eV. Positive sign of Seebeck coefficient for this material indicates holes as dominant charge carriers. Oxidized BaErMn2O6 possesses much higher electrical conductivity, almost 0.2Scm−1 at room temperature. Additional, about 10-fold increase of electrical conductivity, occurring in the vicinity of 225°C for this material, can be associated with phase transition from charge/orbital-ordered insulator COI(CE) to paramagnetic metal PM phase. The highest conductivity for BaErMn2O6 was measured near 500°C and is almost equal to 40Scm−1, while negative sign of Seebeck coefficient can be associated with electrons being dominant charge carriers. [ABSTRACT FROM AUTHOR]

Abstract: Physicochemical properties of La1−xBaxCo0.2Fe0.8O3−δ (LBCF) oxides are presented in aspect of their possible application as cathode materials in Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC). The obtained results show that the increase of concentration of Ba2+ leads to an increase of unit cell volume and to a decrease of crystal structure distortion, which is accompanied by an increase of the level of oxygen nonstoichiometry in the studied compounds. For samples with x≥0.6 cubic structure was observed, which is particularly worth noting for BaCo0.2Fe0.8O3−δ composition, as both BaCoO3−δ and BaFeO3−δ often, but depending on oxygen nonstoichiometry δ, adopt hexagonal-type structure. Electrical conductivity and Seebeck coefficient data of the materials are quite similar, comparing to La1−xSrxCo1−yFeyO3−δ oxides. For samples with barium content ≥0.6, at high temperatures, a clearly visible maximum on electrical conductivity dependence on temperature can be seen, which may be related to a significant increase of the oxygen nonstoichiometry. The highest conductivity in the intermediate temperature range (600–800°C) was observed for La0.6Ba0.4Co0.2Fe0.8O3−δ composition, however obtained values are significantly lower, comparing to strontium analog: La0.6Sr0.4Co0.2Fe0.8O3−δ. La0.6Ba0.4Co0.2Fe0.8O3−δ oxide was used as the cathode material in custom-made button-type IT-SOFCs, which properties were evaluated in 600–800°C temperature range. Additionally, chemical stability of that material in relation to Ce0.8Gd0.2O1.9 electrolyte was studied. [Copyright &y& Elsevier]

Abstract: Oxides with perovskite structure and composition: La0.5Sr0.5Co0.5Fe0.5O3−δ , La0.5Ba0.5Co0.5Fe0.5O3−δ , Sm0.5Sr0.5Co0.5Fe0.5O3−δ and Sm0.5Ba0.5Co0.5Fe0.5O3−δ were synthesized by a sol–gel EDTA based method. Their physico-chemical properties were evaluated by structural (XRD), transport (electrical conductivity, Seebeck coefficient), and high temperature oxygen nonstoichiometry measurements (TG, δ). A distorted perovskite structure was observed for all of the samples, varying with A-site average radius of cations and tolerance factor t. TG measurements, which were performed in air and in reducing atmosphere allowed to determine the initial, as well as the high temperature dependence of the oxygen nonstoichiometry δ for all materials. At high temperatures the electrical conductivity of the measured samples showed a characteristic maximum and corresponding increase of the Seebeck coefficient. Both effects can be interpreted as a result of a formation of the oxygen vacancies. Apart from Sm0.5Ba0.5Co0.5Fe0.5O3−δ composition, all other materials possess very high electrical conductivity at high temperatures, well exceeding 100Scm−1. A custom made IT-SOFC cells were constructed with Ce0.85Gd0.15O1.925 sinters as a support. Their performance was evaluated in 600–800°C range. Despite rather similar transport properties of La0.5Sr0.5Co0.5Fe0.5O3−δ , La0.5Ba0.5Co0.5Fe0.5O3−δ and Sm0.5Sr0.5Co0.5Fe0.5O3−δ perovskites, the best electrochemical properties were recorded in case of the cell with La0.5Sr0.5Co0.5Fe0.5O3−δ based cathode. [Copyright &y& Elsevier]

Phase composition, crystal structure, and selected physicochemical properties of the high entropy Ln(Co,Cr,Fe,Mn,Ni)O3−δ (Ln = La, Pr, Gd, Nd, Sm) perovskites, as well as the possibility of Sr doping in Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ series, are reported is this work. With the use of the Pechini method, all undoped compositions are successfully synthesized. The samples exhibit distorted, orthorhombic or rhombohedral crystal structure, and a linear correlation is observed between the ionic radius of Ln and the value of the quasi-cubic perovskite lattice constant. The oxides show moderate thermal expansion, with a lack of visible contribution from the chemical expansion effect. Temperature-dependent values of the total electrical conductivity are reported, and the observed behavior appears distinctive from that of non-high entropy transition metal-based perovskites, beyond the expectations based on the rule-of-mixtures. In terms of formation of solid solutions in Sr-doped Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ materials, the results indicate a strong influence of the Ln radius, and while for La-based series the Sr solubility limit is at the level of xmax = 0.3, for the smaller Pr it is equal to just 0.1. In the case of Nd-, Sm- and Gd-based materials, even for the xSr = 0.1, the formation of secondary phases is observed on the SEM + EDS images. [ABSTRACT FROM AUTHOR]

It has been documented that the total electrical conductivity of the hexagonal rare-earth manganites Y0.95Pr0.05MnO3+δ and Y0.95Nd0.05MnO3+δ, as well as the undoped YMnO3+δ, is largely dependent on the oxygen excess δ, which increases considerably at temperatures below ca. 300 °C in air or O2. Improvement for samples maintaining the same P63cm crystal structure can exceed 3 orders of magnitude below 200 °C and is related to the amount of the intercalated oxygen. At the same time, doping with Nd3+ or Pr3+ affects the ability of the materials to incorporate O2, and therefore indirectly influences the conductivity as well. At high temperatures (700–1000 °C) and in different atmospheres of Ar, air, and O2, all materials are nearly oxygen-stoichiometric, showing very similar total conduction with the activation energy values of 0.8–0.9 eV. At low temperatures in Ar (δ ≈ 0), the mean ionic radius of Y1−xLnx appears to influence the electrical conductivity, with the highest values observed for the parent YMnO3. For Y0.95Pr0.05MnO3+δ oxide, showing the largest oxygen content changes, the recorded dependence of the Seebeck coefficient on the temperature in different atmospheres exhibits complex behavior, reflecting oxygen content variations, and change of the dominant charge carriers at elevated temperatures in Ar (from electronic holes to electrons). Supplementary cathodic polarization resistance studies of the Y0.95Pr0.05MnO3+δ electrode document different behavior at higher and lower temperatures in air, corresponding to the total conduction characteristics. [ABSTRACT FROM AUTHOR]

Fully-stoichiometric SmBaCo2-xMnxO6 oxides (x = 0, 0.5, 1) were obtained through the electrochemical oxidation method performed in 1 M KOH solution from starting materials having close to equilibrium oxygen content. Cycling voltammetry scans allow us to recognize the voltage range (0.3–0.55 V vs. Hg/HgO electrode) for which electrochemical oxidation occurs with high efficiency. In a similarly performed galvanostatic experiment, the value of the stabilized voltage recorded during the oxidation increased with higher Mn content, which seems to relate to the electronic structure of the compounds. Results of the iodometric titration and thermogravimetric analysis prove that the proposed technique allows for an increase in the oxygen content in SmBaCo2-xMnxO5+δ materials to values close to 6 (δ ≈ 1). While the expected significant enhancement of the total conductivity was observed for the oxidized samples, surprisingly, their crystal structure only underwent slight modification. This can be interpreted as due to the unique nature of the oxygen intercalation process at room temperature. [ABSTRACT FROM AUTHOR]

The influence of the material's crystal structure and morphology of the electrode layer on the electrocatalytic activity toward the oxygen reduction reaction is studied for the selected perovskite-type oxygen electrode materials for Solid Oxide Fuel Cells. The A-site cation-disordered Sm 0.5 Ba 0.25 Sr 0.25 Co 0.5 Cu 0.5 O 3-δ with Pm -3 m cubic perovskite, obtained previously by the electrospinning method (ES), and compound with the same ratio of cations, the A-site cation-ordered SmBa 0.5 Sr 0.5 CoCuO 5+δ, prepared by a typical sol-gel route (SG), P 4/ mmm double perovskite are considered. It is documented that both compounds differ in their basic physicochemical properties, while the ES-based electrode layer shows higher electrocatalytic activity, and exhibits improved long-term stability. The reasons behind the enhancement are uncovered, with i.a. distribution of relaxation times analyses enabling a deeper insight into the attained modifications. It is found that better performance of the ES electrode cannot be solely explained as due to the changed morphological features, but stems also from the altered physicochemical properties of the active material. The developed ES electrode exhibits the polarization resistance of 0.18 Ω cm2 at 700 °C, and 0.04 Ω cm2 at 800 °C, which is ca. four times lower in comparison to the SG-based one. Also, for an anode-supported cell, the registered power density output is over 260 mW cm−2 at 700 °C, and close to 400 mW cm−2 at 750 °C. [Display omitted] [ABSTRACT FROM AUTHOR]

Recently, layered Li1+xV1−xO2 with x≥0 has attracted significant attention as an anode material for Li-ion batteries. Its high volumetric and gravimetric capacities (1360mAh·cm−3 and 300mAh·g−1 respectively) make it particularly interesting. During lithium intercalation Li1+xV1−xO2 with x>0 exhibits wide potential plateau below 0.1V vs. Li/Li+, while for stoichiometric LiVO2 lithium uptake hardly occurs. In this work evaluation of crystal structure, transport and electrochemical properties is given for Li1+xV1−xO2 materials with x=0, 0.03 and 0.07. Li1+xV1−xO2 showed activated character of conductivity with activation energy about 0.2–0.3eV. Thermoelectric power values exceeding 80μV·K−1 point to electron holes as the main charge carriers. Thermogravimetric measurements carried out in air indicated only minor variations of mass of the materials up to 215°C, suggesting high stability along with low level of oxygen nonstoichiometry. [ABSTRACT FROM AUTHOR]

Abstract: Cu-doped La1.7Ca0.3NiO4+δ has been synthesized and evaluated as potential intermediate-temperature solid oxide fuel cell cathode materials. The effects of Cu substitution for Ni on lattice structure, sinterability, electrical and electrochemical properties of La1.7Ca0.3NiO4+δ are investigated. Cu-doping significantly enhances the sintering activity of La1.7Ca0.3Ni1−x Cu x O4+δ . With increasing content of Cu, both the electronic conductivities and electrochemical performance remarkably increase, leading to an attractive cell performance. The increased conductivity may be related with the elongated Ni(Cu)O6 octahedron in perovskite layers while the decreased polarization resistance mainly correlates with the improved oxygen transport property induced by replacement of Ni by Cu. Single cell test suggests that La1.7Ca0.3Ni1−x Cu x O4+δ is a promising candidate for solid oxide fuel cell cathode. [Copyright &y& Elsevier]

Abstract: Novel, Sr-substituted A-site ordered perovskites with GdBa0.5Sr0.5Co2−xFexO5+δ (0 ≤ x ≤ 2) chemical composition were studied, and results of measurements of their phase composition, crystal structure, oxygen content δ, transport properties and chemical stability in relation to ceria electrolyte are presented in this work. It was found that despite 50% substitution of Ba by Sr, the tendency of ordering in A-sublattice is retained in Co-rich materials, but with the increase of iron content, a significant amount of unordered, but also perovskite phase appears. Compounds with high Co content possess highest electrical conductivity, which for GdBa0.5Sr0.5Co2O5+δ greatly exceeds 1000 S cm−1 at temperatures above 400 °C. Seebeck coefficient remains positive for all studied compositions in 25–850 °C temperature range, indicating dominance of holes as main charge carriers. The double perovskite structure is responsible for a high deviation from the oxygen stoichiometry in studied materials, which increases considerably above 300 °C. GdBa0.5Sr0.5Co1.5Fe0.5O5+δ cathode material was selected for additional studies, which included evaluation of thermal expansion, determination of chemical diffusion coefficient D and surface exchange reaction coefficient K and electrochemical measurements in a custom made, electrolyte-supported Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). At 800 °C value of D is close to 10−5 cm2 s−1, which together with high concentration of oxygen vacancies points to a high ionic conductivity of the material. Together with total electrical conductivity exceeding 400 S cm−1 in 600–800 °C range, and with high chemical stability in relation to ceria electrolyte, the observed properties are attractive from the point of view of application. However, due to a large chemical expansion, in order to obtain good adhesion between cathode and electrolyte layers, composite cathodes, consisting of GdBa0.5Sr0.5Co1.5Fe0.5O5+δ and ceria electrolyte powders had to be used. Recorded power density of IT-SOFC cell was about 0.27 W cm−2 at 800 °C, while the performed impedance spectroscopy studies revealed that ohmic component was the dominant one above 700 °C in total polarization of the cell. [Copyright &y& Elsevier]

• (Ce,Gd,Nd,Sm,Pr,Mo x)O 2- δ and (Ce,Gd,Nd,Sm,Pr,Mo x)O 2- δ , x = (0−0.5) are synthesized. • Addition of Mo x ≥ 0.3 allows stabilizing single-phase fluorite structure. • Mo acts as a substitutional dopant, with Mo6+ valence state. • The stabilization mechanism resembles the one in δ-Bi 2 O 3 -based materials. • Electrical measurements indicate mixed ionic-electronic behavior. (Ce,Gd,Nd,Sm,Pr)O 2- δ and (Ce,Gd,La,Nd,Pr)O 2- δ rare-earth high-entropy oxides (HEOx) with the oxygen vacancy-ordered Ia- 3 structure are doped with a small amount of molybdenum, to prepare two series of materials, (Ce,Gd,Nd,Sm,Pr,Mo x)O 2- δ and (Ce,Gd,Nd,Sm,Pr,Mo x)O 2- δ with x = (0, 0.1, 0.2, 0.3 and 0.5). The first-ever stabilization of the fluorite-type Fm- 3 m structure (i.e. with disordered vacancies) in the ceria-based HEOx is achieved. Structural, microstructural and transport properties of the compounds are systematically studied. The substitution level of x ≥ 0.3 allows to fully stabilize Fm- 3 m symmetry, with samples exhibiting good homogeneity. Influence of Mo on the oxygen vacancy concentration and charge state of the elements is studied with the use of Raman spectroscopy and XPS methods, showing decrease of the vacancy content and dominating presence of Mo6+, Ce4+ and mixed Pr3+/4+ states. Measured for the first time in this group of materials, the electrical conductivity of the Mo-doped oxides indicates the mixed ionic-electronic behavior. [ABSTRACT FROM AUTHOR]

In this work we present results of studies of In3+ doping in strontium cerate, comprising structural aspects, and oxygen as well as proton conductivity. Crystal structure analysis of single-phase SrCe 1-x In x O 3-a (x ​= ​0.1, 0.2 and 0.3) materials in 25–900 ​°C temperature range indicates presence of strong orthorhombic distortion of the perovskite-type structure, similar as for the undoped SrCeO 3. Limited sinterability of the obtained powders was mitigated by addition of 1 ​wt% of NiO, which allowed to manufacture dense sinters at 1400 ​°C. Electrochemical impedance spectroscopy measurements done in dry synthetic air show decrease of the ionic (oxygen) conductivity with the increase of In content, as well as associated increase of the activation energy. This indicates that formed oxygen vacancies are trapped in the structure. Overall, electrical conductivity for SrCe 1-x In x O 3-a in H 2 O- and D 2 O-containing atmospheres decreases with In content, but respective H+ and D+ transference numbers are larger for samples with higher indium doping. At 500 ​°C the highest proton and deuterium conductivity was recorded for SrCe 0.9 In 0.1 O 3-a , reaching up to 0.70·10−4 ​S ​cm−1 and 0.26·10−4 ​S ​cm−1, respectively. Derived diffusion and surface exchange coefficients are 10−7-10−6 ​cm2 ​s−1 and 10−6-10−5 ​cm ​s−1, respectively in 500–700 ​°C temperature range. Pnma symmetry for SrCe 0.7 In 0.3 O 3-a remains stable up to 900 ​°C in air. The hydrated material exhibits high proton transference numbers, which remain above 0.5 up to ca. 500 ​°C. Compound is characterized by low thermal expansion coefficient and relatively high values of transport coefficients, as derived from electrical conductivity relaxation experiments. Image 1 • Addition of 1 ​wt% of NiO allows to obtain dense sinters of SrCe 1-x In x O 3-a (x ​= ​0.1, 0.2 and 0.3). • Pmna crystal structure of SrCe 1-x In x O 3-a materials is stable up to 900 ​°C in air. • With the increasing In doping oxygen conductivity of SrCe 1-x In x O 3-a decreases, while the activation energy increases. • Proton and deuterium conductivity also decrease with In content in SrCe 1-x In x O 3-a. • Highest proton/deuterium transference number are observed for increase with the indium content in SrCe 0.7 In 0.3 O 3-a. [ABSTRACT FROM AUTHOR]

• Solid state solution is formed for Ni-rich Nd 2-x Ni 1-y Cu y O 4±δ (x = 0, 0.1) materials. • Total oxygen content in Nd 2 Ni 1-y Cu y O 4±δ and Nd 1.9 Ni 1-y Cu y O 4±δ decreases for materials having higher amount of copper introduced. • The cation-deficient Nd 1.9 Ni 0.75 Cu 0.25 O 4±δ possesses improved electrical conductivity in Ar atmosphere at high temperatures. • The A-site deficiency in Nd 2-x Ni 0.75 Cu 0.25 O 4±δ enhances bulk diffusion, but hinders surface exchange. • CO 2 -stable Nd 1.9 Ni 0.75 Cu 0.25 O 4±δ membrane with 1.05 mm thickness delivers 0.49 mL cm−2 min−1 oxygen flux at 880 °C. Series of Nd 2-x Ni 1-y Cu y O 4±δ Ruddlesden-Popper-type oxides is obtained by auto-combustion synthesis method and systematically characterized concerning phase composition, formation of solid state solution, crystal structure, oxygen content, as well as regarding transport properties and oxygen permeability when applied as mixed conducting ceramic membranes. The A-site deficiency x is discussed in terms of structural stability and its effect on the oxygen content, with ongoing modification of total electrical conductivity observed. In selected Nd 2-x Ni 0.75 Cu 0.25 O 4±δ oxides the dominating oxygen defects at high temperatures can be changed from oxygen interstitials to vacancies by the induced A-site deficiency, which affects bulk- and surface-related transport coefficients, as it is observed in electrical conductivity relaxation studies. The optimized Nd 1.9 Ni 0.75 Cu 0.25 O 4±δ sinters having increased ionic conductivity, as well as fine, well-sintered microstructure allow to achieve one of the higher reported oxygen fluxes for CO 2 -stable Ruddlesden-Popper-based ceramic membranes (e.g. 0.49 mL cm−2 min−1 at ca. 880 °C for 1.05 mm thickness). [ABSTRACT FROM AUTHOR]

In this work studies on a modification of Cu-based, layered oxides with K 2 NiF 4 -type structure are presented concerning formation of cationic nonstoichiometry in the A-sublattice of the parent La 2 CuO 4 , as well as an introduction of selected M 3 + cations (Sc, Ga, In) at the B-site into La 1.9 Cu 1-x M x O 4 and Ni-containing La 1.9 Cu 0.45 Ni 0.45 M 0.1 O 4 . It is shown that synthesis of phase-pure La 2-x CuO 4 can be done with values of x ≤ 0.1, and in the A-site nonstoichiometric materials further doping with M 3 + is also achievable. Formation of solid solutions for M 3 + -doped samples follows the expected trend, with the widest range observed for the smallest Sc 3 + cation, z ≤ 0.1. Apart from a different structural behavior of the doped oxides at high temperatures, it is documented that the discussed substitution affects strongly the oxygen content ( e.g. high concentration of the oxygen vacancies is present in La 1.9 CuO 4-δ ), as well as electrical conductivity. This is documented by the high-temperature X-ray diffraction, thermogravimetric, iodometic titration and electrical measurements. Since the compounds possess good transport properties, are stable at elevated temperatures, exhibit moderate thermal expansion and are Co-, Sr- and Ba-free, the proposed doping strategy seems interesting concerning development of the oxygen-transporting membranes based on Cu-containing oxides. For example, 1 mm thick La 1.9 Cu 0.9 Sc 0.1 O 4-δ membrane was found to deliver 0.37 mL cm − 2 min − 1 oxygen flux at 950 °C, a very high value for the K 2 NiF 4 -type materials. [ABSTRACT FROM AUTHOR]

BaCo 0.7 Fe 0.3− x In x O 3− δ (BCFI, x =0–0.20) materials, which are considered for application in oxygen separation technology, were prepared by conventional, solid-state reaction process. It was found that doping of indium in x =0.10–0.20 range stabilizes the cubic, perovskite-type structure at ambient temperature. Comprehensive studies were performed considering influence of indium content in BCFI oxides on electrical conductivity, oxygen nonstoichiometry, oxygen permeation behavior and structural stability of the materials. With increasing In content, oxygen vacancy concentration increases, while at the same time, electrical conductivity is found to decrease. Also, the oxygen permeability decreases with increasing In-doping level, which is due to the narrowing of the critical radius and the increasing of the activation energy of oxygen migration. This correlation was further elucidated by first principles calculations. From a point of view of application, incorporation of In enhances structural stability of the compounds in reducing atmospheres, and also, membranes with BaCo 0.7 Fe 0.2 In 0.1 O 3− δ composition exhibited ability to recover the same crystal structure after reduction. For 1 mm thick membranes, a high oxygen permeation flux of about 1.48 mL cm −2 min −1 was measured at 900 °C under air/He gradient conditions. [ABSTRACT FROM AUTHOR]

Abstract: In this work two different Na x CoO2− y oxides (Na0.69CoO2− y and Na0.72CoO2− y ) were studied in terms of their crystal structure, sodium content, oxygen nonstoichiometry, transport properties (electrical conductivity and thermoelectric power) and electrochemical properties in Na/Na+/Na x CoO2− y cells. The materials were prepared by a solid-state method. XRD measurements with Rietveld analysis confirmed the presence of a single phase with P63/mmc symmetry. Oxygen nonstoichiometry, which was calculated on a basis of thermogravimetric reduction experiments was found to be small, not exceeding 0.04mol·mol−1. Electrical conductivity for both compounds shows metallic-type character, while values of thermoelectric power are high at room temperature, but decrease considerably for lower temperatures. Electrochemical studies performed for Na/Na+/Na x CoO2− y cells in 0.68≤ x ≤0.81 range indicated the presence of a step-like voltage curve with two characteristic voltage plateaus visible at potentials of 2.54V and 2.44V vs. metallic Na electrode. Crystal structure and deviation from the oxygen stoichiometry in the studied materials were related to the character of the discharge curve of Na/Na+/Na x CoO2− y cells and changes of transport properties of Na x CoO2− y oxides as a function of sodium content x and oxygen nonstoichiometry y. [Copyright &y& Elsevier]

Abstract: Li-site, Fe-site and P-site substituted LiFePO4 phosphoolivines were synthesized and examined in terms of crystal structure, electrical conductivity, charge–discharge performance in Li/Li+/LiFePO4-type cells, as well as chemical stability against the LiPF6-EC–DEC electrolyte. Despite possible improvement of electrical conductivity of the substituted phosphoolivines, it seems that the optimization of morphology and reduction of grain size is the most efficient way of improvement of electrochemical performance of LiFePO4, while chemical stability of the substituted materials remains high. [Copyright &y& Elsevier]

Abstract: The paper presents crystal structure, transport properties, chemical stability in CO2 atmosphere and thin film membrane preparation for materials from the Ba(Ce1− x Zr x )0.9Nd0.1O2.95 (x =0, 0.25, 0.5, 0.75, 1) group of perovskite-type structure oxides. Transformation of crystal structure from orthorhombic Pnma to orthorhombic Imma and cubic with increasing x Zr was observed along with linear decrease of pseudo-cubic unit cell volume and free lattice volume. Electrical conductivity of bulk and grain boundary was determined in dry air, as well as in air humidified with H2O or D2O. The highest proton conductivity was observed for material with x Zr =0.25. Further increase of Zr content led to decrease of conductivity as high as 2 orders of magnitude. This effect was coupled with bell-shape dependence of activation energy and pre-exponential term. Such behavior was explained as superimposed effects of high proton mobility for zirconium-rich materials due to cubic symmetry and cerium-rich materials due to softness of oxygen–oxygen separation distance, along with high proton concentration for cerium-rich perovskites. The deteriorating effect of grain boundaries on total electrical conductivity was far more pronounced for Zr-rich materials than in the case of Ce-rich ones. Declining grain boundary conductivity was attributed to both increase of number of grain boundaries and decrease of inherent grain boundary conductivity for Zr-rich samples. The highest chemical stability in CO2 atmosphere was achieved for high-Zr content materials, on the contrary, for BaCe0.9Nd0.1O2.95 in CO2 atmosphere, the decomposition onset temperature was below 500°C. 2μm thin film membrane of Ba(Ce0.75Zr0.25)0.9Nd0.1O2.95 was successfully prepared on c-plane sapphire and fused silica substrates. Film''s crystal structure matched that of the bulk material. The electrical conductivity of thermally treated film obtained on c-plane sapphire in wet air was 3.7×10−4 S cm−1 at 600°C. [Copyright &y& Elsevier]

A series of the high-entropy (Co,Cu,Mg,Ni,Zn) 1- x Li x O oxides with a lithium substitution level of x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 is evaluated in terms of the crystal structure, morphology and transport properties, with thorough studies aimed at elucidation of the nature of different contributions to the total electrical conductivity. It is found that cubic Fm -3 m structure is preserved in the whole investigated series, with (Co,Cu,Mg,Ni,Zn) 0.8 Li 0.2 O composition showing a high internal strain, supporting to some degree one of the so-called core effects, anticipated for the high-entropy materials. For samples with Li content x > 0.20 the strain is relaxed by formation of the oxygen vacancies. As unambiguously evidenced by DC polarization experiments and measured impedance spectroscopy data with ionically-blocking Au and reversible Li electrodes used, the previously reported in the literature transition to the lithium superionic conductivity in the Li-rich compounds, up to σ i ≈ 1–10⋅10−3 Scm−1, is more complex, with emergence of the electronic conduction as well, reaching similar magnitude for (Co,Cu,Mg,Ni,Zn) 0.7 Li 0.3 O. The observed behavior upon increase of lithium concentration (x) can be explained by a qualitative change of the nature of the electronic and ionic defects present in (Co,Cu,Mg,Ni,Zn) 1- x Li x O series, with initial oxidation of 3 d metals (mainly Co), followed by possible formation of the interstitial lithium, and final emergence of the oxygen vacancies. Furthermore, the recorded electrochemical properties of (Co,Cu,Mg,Ni,Zn) 0.7 Li 0.3 O lithium cell electrode, suggesting presence of intercalation-like behavior at the initial stages of lithiation, confirm the proposed mixed ionic-electronic conductivity. [Display omitted] [ABSTRACT FROM AUTHOR]

Nd 2-x Ni 0.75 Cu 0.2 M 0.05 O 4±δ (x ​= ​0 and 0.1; M ​= ​Sc, Ga, and In) Ruddlesden-Popper-type oxides are obtained by a sol-gel route and characterized concerning phase composition and crystal structure. It is found that the largest In3+ cannot be effectively introduced into the structure, while Nd stoichiometric and cation-deficient Nd 2-x Ni 0.75 Cu 0.2 Sc 0.05 O 4±δ and Nd 2-x Ni 0.75 Cu 0.2 Ga 0.05 O 4±δ (x ​= ​0; 0.1) can be obtained as single-phase materials. Systematic characterization of the crystal structure at high temperatures, oxygen content, as well as transport properties reveals that while the Nd-site deficiency has rather negligible influence on the structure, it causes a substantial decrease of the oxygen content, which at high temperatures leads to a change of the dominant type of defects from the oxygen interstitials to the vacancies for Nd 1.9 Ni 0.75 Cu 0.2 Sc 0.05 O 4±δ and Nd 1.9 Ni 0.75 Cu 0.2 Ga 0.05 O 4±δ. The Nd-site deficiency also causes a decrease of the total conductivity. Importantly, all the examined materials exhibit full chemical stability in CO 2 atmosphere, which together with moderate thermal expansion makes them good candidates for the oxygen transport membranes, which can be used e.g. in the air separation technologies. The selected Sc- and Ga-doped compounds evaluated as ceramic membranes show relatively high oxygen fluxes, with the highest value of 0.78 ​mL ​cm-2 min-1 at ca. 880 ​°C registered for 0.9 ​mm thick, dense Nd 1.9 Ni 0.75 Cu 0.2 Ga 0.05 O 4±δ membrane. Image 1 • Solid state solution is formed for the Sc- and Ga-substituted Nd 2-x Ni 0.75 Cu 0.2 M 0.05 O 4±δ ​(x=0, 0.1; M: Sc, Ga, In) materials. • Crystal structure and oxygen stoichiometry of Nd 2-x Ni 0.75 Cu 0.2 M 0.05 O 4±δ at high temperatures. • Nd-site nonstoichiometry causes decrease of oxygen content and electrical conductivity. • Nd 1.9 Ni 0.75 Cu 0.2 Ga 0.05 O 4±δ membrane with 0.9 ​mm thickness delivers 0.78 ​mL ​cm-2 min-1 oxygen flux at 880 ​°C. [ABSTRACT FROM AUTHOR]