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Among the for the first time reported Cr-containing high entropy La1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) perovskite-type oxides, the selected Sr-doped La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ material is documented to possess attractive properties as a candidate air electrode material for Solid Oxide Fuel Cells (SOFCs). Nanosized powders of the considered oxides are obtained using a modified Pechini sol–gel method. In the formed solid solution with a simple perovskite structure the strontium solubility limit is found to be at least x = 0.3. Room temperature (RT) structural data indicate the presence of rhombohedral structural distortion (R3¯c symmetry) in the materials. High-temperature structural studies for the selected La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ indicate the occurrence of a phase transition to an aristotype Pm3¯m structure at ca. 800 °C. The linear thermal expansion coefficient in the RT-1000 °C range is found to be moderate, 16.0(3) × 10−6 K−1. The results of impedance spectroscopy measurements support the semiconducting-type behavior of the electrical conductivity for all single-phase materials, in a temperature range of RT-1000 °C. The maximum recorded conductivity for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ composition exceeds 16 S cm−1 in the 900–1000 °C range, being suitable for application. Furthermore, chemical stability toward the La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte is proven. Considering the presence of chromium, typically deleterious to the performance, the measured value of the total cathodic polarization resistance for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ-based electrode, being 0.126 Ω cm−2 at 900 °C, seems to be very attractive. The results obtained for a button-type fuel cell indicate power densities at a level of 550 mW cm−2 at 900 °C. Therefore, it can be considered that the high entropy-based approach enables to propose alternative SOFC air electrode materials, with otherwise inaccessible chemical compositions. [ABSTRACT FROM AUTHOR]

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]

[Display omitted] • A protective coating based on SiAlOC glasses was applied on the Crofer 22APU steel. • The outstanding improvement in the oxidation resistance was obtained. • Raman Confocal Imaging was applied to determine the structure of oxidized samples. • The SiAlOC coating entrapped nucleating phases, hence suppression of diffusion. • The formation of Si-O-Cr bridges was established as mechanism. In this work, the potential of using Polymer Derived Ceramics based on SiAlOC glasses in the form of protective thin layers was demonstrated on Ferritic Stainless Steel (FSS) Crofer 22APU steel, an alloy often used for intermediate- and low-temperature Solid Oxide Fuel Cells (SOFC's) interconnects. Microstructural features were investigated by the detailed analysis combining Electron Probe Micro Analysis (EPMA) and Raman Confocal imaging (surface imaging and depth profiling), which revealed the formation of Si-O-Cr bridges, believed to play a crucial role to slow down oxidation of the steel. Additionally, the positive role of aluminum introduced into the SiOC system, which enhances the suppression of the degradation by transport processes. The most crucial value of such findings is the formation of a flexible coating material (SiAlOC glasses) that may be applied on a wide range of FSSs increasing their heat resistance. The application of the combination of methods to determine both chemical (EPMA) and phase (Raman) composition of a multi-layered complex system is also demonstrated. [ABSTRACT FROM AUTHOR]

Phase composition, crystal structure, and selected physicochemical properties of the high entropy Ln(Co,Cr,Fe,Mn,Ni)O 3-δ (Ln = La, Pr, Gd, Nd, Sm) perovskites, as well as the possibility of Sr doping in Ln 1 -x Sr x (Co,Cr,Fe,Mn,Ni)O 3-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 Ln 1- x Sr x (Co,Cr,Fe,Mn,Ni)O 3-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 x max = 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 x Sr = 0.1, the formation of secondary phases is observed on the SEM + EDS images.