Among reported for the first time 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...

No abstract

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.

High entropy oxides (HEOs), based on the incorporation of multiple‐principal cations into the crystal lattice, offer the possibility to explore previously inaccessible oxide compositions and unconventional properties. Here it is demonstrated that despite the chemical complexity of HEOs external stimuli, such as epitaxial strain, can selectively stabilize certain magneto‐electronic states. Epitaxial (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4‐HEO thin films are grown in three different strain states: tensile, compressive, and relaxed. A unique coexistence of rocksalt and spinel‐HEO phases, which are fully coherent with no detectable chemical segregation, is revealed by transmission electron microscopy. This dual‐phase coexistence appears as a universal phenomenon in (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4 epitaxial films. Prominent changes in the magnetic anisotropy and domain structure highlight the strain‐induced bidirectional control of magnetic properties in HEOs. When the films are relaxed, their magnetization behavior is isotropic, similar to that of bulk materials. However, under tensile strain, the hardness of the out‐of‐plane (OOP) axis increases significantly. On the other hand, compressive straining results in an easy OOP magnetization and a maze‐like magnetic domain structure, indicating the perpendicular magnetic anisotropy. Generally, this study emphasizes the adaptability of the high entropy design strategy, which, when combined with coherent strain engineering, opens additional prospects for fine‐tuning properties in oxides.

High-entropy (La,Pr,Nd,Sm,Gd)BaCo2O5+δ double perovskite-type oxide having an equimolar, high-entropy, A-site-layered arrangement of cations is synthesized for the first time. A modified Pechini method, followed by calcination and sintering at 1,100°C helps in obtaining a single-phase, homogenous material with tetragonal I4/mmm symmetry. In situ X-ray diffraction and dilatometric studies show excellent phase stability up to 1,100°C in air, with the average thermal expansion coefficient of 23.7∙10–6 K−1 within the 25–1,100°C range. Total electrical conductivity of the metallic character exceeds 1,600 S cm−1 at room temperature. Equilibrated oxygen content at room temperature is determined as 5.69. The cathodic polarization resistance of the (La,Pr,Nd,Sm,Gd)BaCo2O5+δ layers, manufactured on the La0.8Sr0.2Ga0.8Mg0.2O2.8 (LSGM) solid electrolyte of proved inertness, is as low as 0.037 Ω cm2 at 900°C, and 0.175 Ω cm2 at 750°C. The determined value of the power density in the LSGM-based, electrolyte-supported (thickness ca. 200 μm) fuel cell reaches 857 mW cm−2. These results indicate possible applicability of the developed cathode material for solid oxide fuel cells, making it also one of the best-performing high-entropy air electrodes reported until now. However, the determined physiochemical characteristics of the material indicate a relatively limited influence of the high-entropy A-site arrangement in comparison to the conventional analogs, including the synthesized Nd0.88Sm0.12Co2O5+δ composition, characterized by the same effective radius of the lanthanide cations.