Journal articles: 'High entropy oxide'

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Bridges, Craig A., Bishnu Prasad Thapaliya, Albina Borisevich, Juntian Fan, and Sheng Dai. "(Invited) High Entropy Multication Oxide Battery Materials." ECS Meeting Abstracts MA2022-02, no. 1 (2022): 29. http://dx.doi.org/10.1149/ma2022-02129mtgabs.

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High entropy oxides (HEOs), in which multication occupation of a single crystallographic site plays an important role in the properties, have become relevant in energy storage [1,2], catalysis [3.4], and many more areas. In a subset of these compounds the entropy, rather than enthalpy, plays a dominant role in stabilizing a single-phase structure at high temperatures. In other cases, the multication occupation merely contributes to stability and properties, but the entropy remains dominant in the stability. The field originated with high entropy metal alloys (HEAs)[5], and then expanded to oxides, borides, sulfides, and more. In the case of HEOs, the first example is the rock salt (Mg0.2Ni0.2Co0.2Cu0.2Zn0.2)O, which has generated a great deal of interest in this class of materials.[6,7] It has been shown that HEOs are of interest for high ionic conductivity and electrochemical energy storage. We have examined the electrochemical performance of new high entropy elecrolytes and found an effect of composition on the cycling performance. Samples were prepared through sol-gel routes and high energy milling of starting binary oxides. We have investigated the synthesis using high temperature in-situ X-ray diffraction on a Panalytical diffractometer equipped with an XRK900 stage. STEM/EDS studies on ex-situ samples will be presented that show elemental distribution, with Raman and EIS measurements providing information on ionic diffusion. The results of this study will be highly impactful for the growing community of researchers investigating the design and synthesis of the new class of materials, the high entropy oxides. [1] Q. Wang, et. al., Multi-anionic and -cationic compounds: new high entropy materials for advanced Li-ion batteries, Energy Environ. Sci., 2019, 12, 2433; [2] D. Berardan, et. al., Room temperature lithium superionic conductivity in high entropy oxides, J. Mater. Chem. A, 2016, 4, 9536.; [3] H. Chen, et al., Mechanochemical Synthesis of High Entropy Oxide Materials under Ambient Conditions: Dispersion of Catalysts via Entropy Maximization, ACS Materials Lett. 2019, 1, 1, 83–88; [4] H. Chen, et. al., Entropy-stabilized metal oxide solid solutions as CO oxidation catalysts with high-temperature stability, J. Mater. Chem. A 2018, 6, 11129-11133; [5] Y. Lu, et. al., Sci. Rep. 4, 6200 (2014); Y. F. Ye, et. al., Mater. Today 19 (6), 349 (2016); Zhang, Y., et. al., Nature Commun. 6, 8736 (2015); [6] C. M. Rost, et. al., Nature Commun. 6, 8485 (2015); [7] B. Jiang, et. al., Probing the Local Site Disorder and Distortion in Pyrochlore High-Entropy Oxides. Journal of the American Chemical Society 2021, 143, (11), 4193-4204

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Meisenheimer, P. B., and J. T. Heron. "Oxides and the high entropy regime: A new mix for engineering physical properties." MRS Advances 5, no. 64 (2020): 3419–36. http://dx.doi.org/10.1557/adv.2020.295.

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AbstractHistorically, the enthalpy is the criterion for oxide materials discovery and design. In this regime, highly controlled thin film epitaxy can be leveraged to manifest bulk and interfacial phases that are non-existent in bulk equilibrium phase diagrams. With the recent discovery of entropy-stabilized oxides, entropy and disorder engineering has been realized as an orthogonal approach. This has led to the nucleation and rapid growth of research on high-entropy oxides – multicomponent oxides where the configurational entropy is large but its contribution to its stabilization need not be significant or is currently unknown. From current research, it is clear that entropy enhances the chemical solubility of species and can realize new stereochemical configurations which has led to the rapid discovery of new phases and compositions. The research has expanded beyond studies to understand the role of entropy in stabilization and realization of new crystal structures to now include physical properties and the roles of local and global disorder. Here, key observations made regarding the dielectric and magnetic properties are reviewed. These materials have recently been observed to display concerted symmetry breaking, metal-insulator transitions, and magnetism, paving the way for engineering of these and potentially other functional phenomena. Excitingly, the disorder in these oxides allows for new interplay between spin, orbital, charge, and lattice degrees of freedom to design the physical behavior. We also provide a perspective on the state of the field and prospects for entropic oxide materials in applications considering their unique characteristics.

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Oh, Seeun, Dongyeon Kim, and Kang Taek Lee. "High Entropy Perovskite Electrolytes for Reversible Protonic Ceramic Electrochemical Cells." ECS Meeting Abstracts MA2023-01, no. 54 (2023): 270. http://dx.doi.org/10.1149/ma2023-0154270mtgabs.

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Reversible protonic ceramic electrochemical cells (R-PCECs) become cornerstones of low-temperature solid oxide electrochemical cells (SOCs) below 600 °C. Low activation energy and high energy conversion efficiency are primary significance of R-PCECs. However, electrolytes of high-performance R-PCECs still suffer from poor tolerance to complex operating conditions. To overcome their low stability and enhance proton conductivity, various cations have been doped into the Ba-based perovskite oxide electrolyte. Developing high entropy oxides by introducing multiple metal cations into A- or B- sites of the perovskite structure can be an effective solution for the structural stability. Due to the effect of the entropy-dominated stabilization in multi-doped perovskite oxides, the material can remain single phase under extreme temperatures and chemical environments. Promising high entropy stabilization concepts were adapted to electrolytes, and finally, durable proton-conducting perovskite oxide was designed. Here, we will present our recent progress on development of high entropy perovskite oxide electrolytes for R-PCECs.

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Oh, Seeun, Dongyeon Kim, and Kang Taek Lee. "High Entropy Perovskite Electrolytes for Reversible Protonic Ceramic Electrochemical Cells." ECS Transactions 111, no. 6 (2023): 1743–49. http://dx.doi.org/10.1149/11106.1743ecst.

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Reversible protonic ceramic electrochemical cells (R-PCECs) have become the cornerstone of low-temperature solid oxide electrochemical cells (SOCs) below 600 °C. Low activation energy and high energy conversion efficiency are primary significance of R-PCECs. However, electrolytes of high-performance R-PCECs still suffer from poor tolerance to complex operating conditions. To overcome their low stability and enhance proton conductivity, various cations have been doped into the Ba-based perovskite oxide electrolyte. Developing high entropy oxides by introducing multiple metal cations into A- or B- sites of the perovskite structure can be an effective solution for the structural stability. Due to the effect of the entropy-dominated stabilization in multi-doped perovskite oxides, the material can remain single phase under extreme temperatures and chemical environments. Promising high entropy stabilization concepts were adapted to electrolytes, and finally, durable proton-conducting perovskite oxide was designed. Here, we will present our recent progress on development of high entropy perovskite oxide electrolytes for R-PCECs.

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Li, Haoyang, Yue Zhou, Zhihao Liang, et al. "High-Entropy Oxides: Advanced Research on Electrical Properties." Coatings 11, no. 6 (2021): 628. http://dx.doi.org/10.3390/coatings11060628.

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The concept of “high entropy” was first proposed while exploring the unknown center of the metal alloy phase diagram, and then expanded to oxides. The colossal dielectric constant found on the bulk high-entropy oxides (HEOs) reveals the potential application of the high-entropy oxides in the dielectric aspects. Despite the fact that known HEO thin films have not been reported in the field of dielectric properties so far, with the high-entropy effects and theoretical guidance of high entropy, it is predictable that they will be discovered. Currently, researchers are verifying that appropriately increasing the oxygen content in the oxide, raising the temperature and raising the pressure during preparation have an obvious influence on thin films’ resistivity, which may be the guidance on obtaining an HEO film large dielectric constant. Finally, it could composite a metal–insulator–metal capacitor, and contribute to sensors and energy storage devices’ development; alternatively, it could be put into application in emerging thin-film transistor technologies, such as those based on amorphous metal oxide semiconductors, semiconducting carbon nanotubes, and organic semiconductors.

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Sharma, Yogesh, Min-Cheol Lee, Krishna Chaitanya Pitike, et al. "High Entropy Oxide Relaxor Ferroelectrics." ACS Applied Materials & Interfaces 14, no. 9 (2022): 11962–70. http://dx.doi.org/10.1021/acsami.2c00340.

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Ding, Yiwen, Keju Ren, Chen Chen, et al. "High-entropy perovskite ceramics: Advances in structure and properties." Processing and Application of Ceramics 18, no. 1 (2024): 1–11. http://dx.doi.org/10.2298/pac2401001d.

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High-entropy ceramic materials usually refer to the multi-principal solid solution formed by 5 or more ceramic components. Due to its novel ?high-entropy effect? and excellent performance, it has become one of the research hotspots in the field of ceramics in recent years. As the research system of high-entropy ceramics has gradually expanded from the initial rock salt oxides (Mg-Ni-Co-Cu-Zn)O to fluorite oxides, perovskite oxides, spinel oxides, borides, carbides and silicates, its special mechanical, electrical, magnetic and energy storage properties have been continuously discovered. Based on the basic principle of high-entropy materials, this paper mainly introduces the prominent perovskite-type oxide high-entropy ceramics in recent years from the perspective of ceramic structure and properties, and predicts the development trend of high-entropy perovskite-type ceramics in the next few years.

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Kajitani, Tsuyoshi, Yuzuru Miyazaki, Kei Hayashi, Kunio Yubuta, X. Y. Huang, and W. Koshibae. "Thermoelectric Energy Conversion and Ceramic Thermoelectrics." Materials Science Forum 671 (January 2011): 1–20. http://dx.doi.org/10.4028/www.scientific.net/msf.671.1.

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Oxide thermoelectrics are relatively new materials that are workable at temperatures in the range of 400K≤T≤1200K. There are several types of thermoelectric oxide, namely, cobalt oxides (p-type semi-conductors), manganese oxides (n-type) and zinc oxides (n-type semi-conductors) for high temperature energy harvesting. The Seebeck coefficient of 3d metal oxide thermoelectrics is relatively high due to either high density of states at Fermi surfaces or spin entropy flow associated with the carrier flow. The spin entropy part dominates the Seebeck coefficient of 3d-metal oxides at temperatures above 300K. Introduction of impurity particles or quantum-well structures to enhance thermionic emission and energy filtering effects for the oxide semiconductors may lead to a significant improvement of thermoelectric performance.

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YILDIZ, İlker. "Synthesis and characterization of b-site controlled la-based high entropy perovskite oxides." Journal of Scientific Reports-A, no. 055 (December 31, 2023): 124–31. http://dx.doi.org/10.59313/jsr-a.1370632.

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High entropy perovskite oxide materials are a highly promising class of materials with a wide range of potential applications. They offer a unique combination of perovskite oxides and high entropy oxides, making them suitable for various fields, particularly in electrochemical energy storage systems and hydrogen production. Given the growing demand for clean energy and efficient energy storage solutions, the development of high entropy materials holds great significance. In this study, a cost-effective and rapid fabrication method was employed to produce several single-phase high entropy perovskite oxides by altering the B-site cations. The results demonstrated that these high entropy perovskite oxides could be synthesized with the same crystal structure, despite having significantly different elemental compositions. These variations in elemental composition led to differences in lattice parameters, metal-oxygen bond strengths, and oxygen vacancy content within the materials. Understanding and manipulating these factors can have important implications for the design of high entropy materials for energy storage and other applications.

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Przygucka, Dominika, Adelajda Polkowska, Wojciech Polkowski, Krzysztof Karczewski, and Stanisław Jóźwiak. "Titanium Oxide Formation in TiCoCrFeMn High-Entropy Alloys." Materials 18, no. 2 (2025): 412. https://doi.org/10.3390/ma18020412.

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High-entropy materials, characterized by complex chemical compositions, are difficult to identify and describe structurally. These problems are encountered at the composition design stage when choosing an effective method for predicting the final phase structure of the alloy, which affects its functional properties. In this work, the effects of introducing oxide precipitates into the matrix of a high-entropy TiCoCrFeMn alloy to strengthen ceramic particles were studied. The particles were introduced by the ex situ method, such as TiO2 in the form of anatase, and by the in situ method, consisting of the reconstruction of CuO into TiO2. In both cases, it was assumed that after the homogenization process, carried out at 1000 °C, ceramic precipitates in the rutile phase, commonly considered a stable allotropic form of TiO2, would be obtained. However, the microscopic observations and XRD analyses, supported by EDS chemical composition microanalysis and EBSD backscattered electron diffraction, clearly revealed that, regardless of the method of introducing oxides, the final strengthening phase obtained was a mixture of TiO2 in the form of anatase with the Magnelli phase of Ti2O3. In this work, phase reconstruction in the Ti-O system was analyzed using changes in the Gibbs free energy of the identified oxide phases.

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Lin, Wei-Chih, Yi-Wen Lien, Louis Etienne Moreau, et al. "High-Temperature Oxidation of NbTi-Bearing Refractory Medium- and High-Entropy Alloys." Materials 17, no. 18 (2024): 4579. http://dx.doi.org/10.3390/ma17184579.

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The oxidation of six NbTi-i refractory medium- and high-entropy alloys (NbTi + Ta, NbTi + CrTa, NbTi + AlTa, NbTi + AlMo, NbTi + AlMoTa and NbTi + AlCrMo) were investigated at 1000 °C for 20 h. According to our observation, increased Cr content promoted the formation of protective CrNbO4 and Cr2O3 oxides in NbTi + CrTa and NbTi + AlCrMo, enhancing oxidation resistance. The addition of Al resulted in the formation of AlTi-rich oxide in NbTi + AlTa. Ta addition resulted in the formation of complex oxides (MoTiTa8O25 and TiTaO4) and decreased oxidation resistance. Meanwhile, Mo’s low oxygen solubility could be beneficial for oxidation resistance while protective Cr2O3/CrNbO4 layers were formed. In NbTi + Ta, NbTi + AlTa and NbTi + CrTa, a considerable quantity of Ti-rich oxide was observed at the interdendritic region. In NbTi + AlCrMo, the enrichment of Cr and Ti at the interdendritic region could fasten the rate of oxidation. Compared to the recent research, NbTi + AlCrMo alloy is a light-weight oxidation-resistant alloy (weight gain of 1.29 mg/cm2 at 1000 °C for 20 h and low density (7.2 g/cm3)).

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Hashishin, Takeshi, Haruka Taniguchi, Fei Li, and Hiroya Abe. "Useful High-Entropy Source on Spinel Oxides for Gas Detection." Sensors 22, no. 11 (2022): 4233. http://dx.doi.org/10.3390/s22114233.

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This study aimed to identify a useful high-entropy source for gas detection by spinel oxides that are composed of five cations in nearly equal molar amounts and free of impurities. The sensor responses of the spinel oxides [1# (CoCrFeMnNi)3O4, 2# (CoCrFeMnZn)3O4, 3# (CoCrFeNiZn)3O4, 4# (CoCrMnNiZn)3O4, 5# (CoFeMnNiZn)3O4, and 6# (CrFeMnNiZn)3O4] were evaluated for the test gases (7 ppm NO2, 5000 ppm H2, 3 ppm NH3, and 3 ppm H2S). In response to NO2, 1# and 2# showed p-type behavior while 3–6# showed n-type semiconductor behavior. There are three p-type and one n-type AO structural compositions in AB2O4[AO·B2O3] type spinel, and 1# showed a stable AO composition because cation migration from site B to site A is unlikely. Therefore, it was assumed that 1# exhibited p-type behavior. The p-type behavior of 2# was influenced by Cr oxide ions that were present at the B site and the stable p-type behavior of zinc oxide at the A site. The spinel oxides 3# to 6# exhibited n-type behavior with the other cationic oxides rather than the dominant p-type behavior exhibited by the Zn oxide ions that are stable at the A site. In contrast, the sensor response to the reducing gases H2, NH3, and H2S showed p-type semiconductor behavior, with a particularly selective response to H2S. The sensor responses of the five-element spinel oxides in this study tended to be higher than that of the two-element Ni ferrites and three-element Ni-Zn ferrites reported previously. Additionally, the susceptibility to sulfurization was evaluated using the thermodynamic equilibrium theory for the AO and B2O3 compositions. The oxides of Cr, Fe, and Mn ions in the B2O3 composition did not respond to H2S because they were not sulfurized. The increase in the sensor response due to sulfurization was attributed to the decrease in the depletion layer owing to electron sensitization, as the top surface of the p-type semiconductors, ZnO and NiO, transformed to n-type semiconductors, ZnS and NiS, respectively. High-entropy oxides prepared using the hydrothermal method with an equimolar combination of five cations from six elements (Cr, Mn, Fe, Co, Ni, and Zn) can be used as a guideline for the design of high-sensitivity spinel-type composite oxide gas sensors.

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Tanveer, Rubayet, and Veerle M. Keppens. "Resonant ultrasound spectroscopy studies of high-entropy fluorites." Journal of the Acoustical Society of America 152, no. 4 (2022): A131. http://dx.doi.org/10.1121/10.0015786.

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High entropy oxides (HEOs), also referred to as multicomponent oxides or compositionally complex oxides (CCOs), have attracted attention due to the tunability of multiple cations on a single site. Since the introduction of HEOs stabilized in the rocksalt phase, the high entropy oxide concept has been expanded to various structures, offering a path for the discovery of innovative compounds with unique structure-property relations. Here, we present a study of high entropy fluorites, which have gained recognition for their low thermal conductivity and possible applications as thermal barrier coatings. We have successfully synthesized single phase samples using multiple cations on a single site, in equimolar and non-equimolar ratios. Resonant ultrasound spectroscopy was used to evaluate the elastic moduli as a function of temperature. The results obtained on these multi-component pyrochlores are compared to those of their single-component counterparts.

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Wang, Junfeng, Qiaobai He, Guanqi Liu, et al. "High-Temperature Oxidation Behavior of AlTiNiCuCox High-Entropy Alloys." Materials 14, no. 18 (2021): 5319. http://dx.doi.org/10.3390/ma14185319.

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In this study, the high-temperature oxidation behavior of a series of AlTiNiCuCox high-entropy alloys (HEAs) was explored. The AlTiNiCuCox (x = 0.5, 0.75, 1.0, 1.25, 1.5) series HEAs were prepared using a vacuum induction melting furnace, in which three kinds of AlTiNiCuCox (x = 0.5, 1.0, 1.5) alloys with different Co contents were oxidized at 800 °C for 100 h, and their oxidation kinetic curves were determined. The microstructure, morphology, structure, and phase composition of the oxide film surface and cross-sectional layers of AlTiNiCuCox series HEAs were analyzed using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD). The influence of Co content on the high-temperature oxidation resistance of the HEAs was discussed, and the oxidation mechanism was summarized. The results indicate that, at 800 °C, the AlTiNiCuCox (x = 0.5, 1.0, 1.5) series HEAs had dense oxide films and certain high-temperature oxidation resistance. With increasing Co content, the high-temperature oxidation resistance of the alloys also increased. With increasing time at high temperature, there was a significant increase in the contents of oxide species and Ti on the oxide film surface. In the process of high-temperature oxidation of AlTiNiCuCox series HEAs, the interfacial reaction, in which metal elements and oxygen in the alloy form ions through direct contact reaction, initially dominated, then the diffusion process gradually became the dominant oxidation factor as ions diffused and were transported in the oxide film.

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Ke, Lingsheng, Long Meng, Sheng Fang, Chun Lin, Mingtian Tan, and Tao Qi. "High-Temperature Oxidation Behaviors of AlCrTiSi0.2 High-Entropy Alloy Doped with Rare Earth La and Y." Crystals 13, no. 8 (2023): 1169. http://dx.doi.org/10.3390/cryst13081169.

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High-entropy alloys (HEAs) were prepared with strong antioxidant metals Al, Cr, Ti, and Si as matrix elements, and the effects of rare earth (RE) lanthanum (La) and yttrium (Y) doping on their microstructures and high-temperature oxidation resistance were explored in this study. The AlCrTiSi0.2RE0.02 HEAs were prepared by using vacuum arc melting and were oxidized mass gain at 1000 °C. After oxidation for 53 h, AlCrTiSi0.2 HEA had a mass increase of 1.195 mg/cm2, and it had the best oxidation resistance of three HEAs (AlCrTiSi0.2, AlCrTiSi0.2La0.02, and AlCrTiSi0.2Y0.02). The surface oxide layers of three HEAs mainly consisted of Al and Ti oxides; the layered oxide film of AlCrTiSi0.2 alloy was mainly composed of dense Al2O3, and the acicular oxide films of AlCrTiSi0.2La0.02 and AlCrTiSi0.2Y0.02 alloys were primarily composed of loose Ti oxide. Doping La and Y decreased the oxidation resistance of AlCrTiSi0.2. In the early stage of oxidation of rare earth HEAs, the surface oxide layer was loose because La and Y reacted with the matrix metal, which slowed down the diffusion of element Al or accelerated the diffusion of element Ti. In the late stage of oxidation, La and Y interacted with O and entered the matrix metal to form rare earth oxides.

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CAYIRLI, Meltem, Esra ERDOGAN-ESEN, Ersu LOKCU, and Mustafa ANIK. "Synthesis and Electrochemical Performance of Spinel Crystal Structured ((FeNiCrMn)1-xCox)3O4 (x=0.1, 0.2, 0.3) High Entropy Oxides." Eurasia Proceedings of Science Technology Engineering and Mathematics 16 (December 31, 2021): 140–44. http://dx.doi.org/10.55549/epstem.1068579.

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High entropy oxides are a new class of materials with a single-phase structure consisting of five or more components. Due to their high structural stability and electrochemical performance, they have attracted a lot of attention in recent years. In this study, high entropy oxides with the composition ((FeNiCrMn)1-xCox)3O4 (x=0.1, 0.2, 0.3) were synthesized using the solid state method and their electrochemical performances as anode material for lithium-ion battery were investigated. Spinel crystal structured of high entropy oxides were characterized by X-ray diffraction (XRD) technique. The electrochemical performance of anodes were evaluated by assembling CR2016 type coin cell. As a result of galvanostatic charge/discharge experiments the initial discharge capacities of ((FeNiCrMn)1-xCox)3O4 (x=0.1, 0.2, 0.3) anodes at a current density of 50 mA g-1 werecalculated as 1993 mA h g-1, 1651 mA h g-1 and 1706 mA h g-1, respectively. Among the synthesized high entropy oxide anodes, the ((FeNiCrMn)0.9Co0.1)3O4 anode shows high initial discharge capacity, while their capacity retention rates at the end of 10th cycle were calculated as 53.9%, 55.1%, 59.7%. This study clearly indicates that the electrochemical performances of high entropy oxide anodes are affected by the Co content.

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Wang, Lin, Quanqing Zeng, Zhibao Xie, Yun Zhang, and Haitao Gao. "High Temperature Oxidation Behavior of an Equimolar Cr-Mn-Fe-Co High-Entropy Alloy." Materials 14, no. 15 (2021): 4259. http://dx.doi.org/10.3390/ma14154259.

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The oxidation behavior of an equimolar Cr-Mn-Fe-Co high-entropy alloy (HEA) processed by 3D laser printing was investigated at 700 °C and 900 °C. The oxidation kinetics of the alloy followed the parabolic rate law, and the oxidation rate constant increased with the rising of the temperature. Inward diffusion of oxygen and outward diffusion of cations took place during the high-temperature oxidation process. A spinel-type oxide was formed on the surface, and the thickness of the oxide layer increased with the rising of experimental temperature or time. The exfoliation of the oxide layer took place when the test was operated at 900 °C over 12 h. During oxidation tests, the matrix was propped open by oxides and was segmented into small pieces. The formation of loose structures had great effects on the high-temperature oxidation resistance of the HEA.

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Xu, Yangsen, Xi Xu, and Lei Bi. "A high-entropy spinel ceramic oxide as the cathode for proton-conducting solid oxide fuel cells." Journal of Advanced Ceramics 11, no. 5 (2022): 794–804. http://dx.doi.org/10.1007/s40145-022-0573-7.

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AbstractA high-entropy ceramic oxide is used as the cathode for the first time for proton-conducting solid oxide fuel cells (H-SOFCs). The Fe0.6Mn0.6Co0.6Ni0.6Cr0.6O4 (FMCNC) high-entropy spinel oxide has been successfully prepared, and the in situ chemical stability test demonstrates that the FMCNC material has good stability against CO2. The first-principles calculation indicates that the high-entropy structure enhances the properties of the FMCNC material that surpasses their individual components, leading to lower O2 adsorption energy for FMCNC than that for the individual components. The H-SOFC using the FMCNC cathode reaches an encouraging peak power density (PPD) of 1052 mW·cm−2 at 700 °C, which is higher than those of the H-SOFCs reported recently. Additional comparison was made between the high-entropy FMCNC cathode and the traditional Mn1.6Cu1.4O4 (MCO) spinel cathode without the high-entropy structure, revealing that the formation of the high-entropy material allows the enhanced protonation ability as well as the movement of the O p-band center closer to the Fermi level, thus improving the cathode catalytic activity. As a result, the high-entropy FMCNC has a much-decreased polarization resistance of 0.057 Ω·cm2 at 700 °C, which is half of that for the traditional MCO spinel cathode without the high-entropy design. The excellent performance of the FMCNC cell indicates that the high-entropy design makes a new life for the spinel oxide as the cathode for H-SOFCs, offering a novel and promising route for the development of high-performance materials for H-SOFCs.

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Dong, Qi, Min Hong, Jinlong Gao, et al. "Rapid Synthesis of High‐Entropy Oxide Microparticles." Small 18, no. 11 (2022): 2104761. http://dx.doi.org/10.1002/smll.202104761.

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Vinnik, Trofimov, Zhivulin, et al. "High Entropy Oxide Phases with Perovskite Structure." Nanomaterials 10, no. 2 (2020): 268. http://dx.doi.org/10.3390/nano10020268.

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The possibility of the formation of high entropy single-phase perovskites using solid-state sintering was investigated. The BaO–SrO–CaO–MgO–PbO–TiO2, BaO–SrO–CaO–MgO–PbO–Fe2O3 and Na2O–K2O–CaO–La2O3–Ce2O3–TiO2 oxide systems were investigated. The optimal synthesis temperature is found between 1150 and 1400 °C, at which the microcrystalline single phase with perovskite structure was produced. The morphology, chemical composition, crystal parameters and dielectric properties were studied and compared with that of pure BaTiO3. According to the EDX data, the single-phase product has a formula of Na0.30K0.07Ca0.24La0.18Ce0.21TiO3 and a cubic structure.

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Hadraba, Hynek, Zdenek Chlup, Antonin Dlouhy, et al. "Oxide dispersion strengthened CoCrFeNiMn high-entropy alloy." Materials Science and Engineering: A 689 (March 2017): 252–56. http://dx.doi.org/10.1016/j.msea.2017.02.068.

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Mileiko, S. T., S. A. Firstov, N. A. Novokhatskaya, V. F. Gorban, and N. P. Krapivka. "Oxide-fibre/high-entropy-alloy-matrix composites." Composites Part A: Applied Science and Manufacturing 76 (September 2015): 131–34. http://dx.doi.org/10.1016/j.compositesa.2015.05.023.

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Vinnik, D. A., E. A. Trofimov, V. E. Zhivulin, et al. "High-entropy oxide phases with magnetoplumbite structure." Ceramics International 45, no. 10 (2019): 12942–48. http://dx.doi.org/10.1016/j.ceramint.2019.03.221.

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Kobayashi, Yasukazu, Shota Yokoyama, and Ryo Shoji. "High-Entropy Alloy Al0.2Co1.5CrFeNi1.5Ti0.5 Prepared from High-Entropy Oxide (Al0.2Co1.5CrFeNi1.5Ti0.5)3O4 by a Deoxidation Process via a CaH2-Assisted Molten Salt Method." Metals 14, no. 4 (2024): 443. http://dx.doi.org/10.3390/met14040443.

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High-entropy alloys (HEAs) have attracted a great deal of research interest these days because of their attractive properties. Low-temperature chemical synthesis methods are being developed to obtain nanoscale HEAs with low energy consumption. In this study, we prepared HEA Al0.2Co1.5CrFeNi1.5Ti0.5 nanoparticles from high-entropy oxide (HEO) (Al0.2Co1.5CrFeNi1.5Ti0.5)3O4 by a deoxidation process via a CaH2-assisted molten salt method at 600 °C. X-ray diffraction measurements demonstrated that the oxide precursor and the reduced product have single-phases of spinel structure and face-centered cubic structures, indicating the formation of HEO and HEA, respectively. The HEA nanoparticles exhibited superior catalytic performance in the liquid-phase hydrogenation of p-nitrophenol at room temperature with little leaching of the component elements. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX) exhibited a good distribution of constituent elements over the HEA nanoparticles in a micro-sized range. However, transmission electron microscopy (TEM) with EDX revealed a slight deviation of elemental distributions of Al and Ti from those of Co, Cr, Fe, and Ni in a nano-sized range, probably due to the incomplete reduction of aluminum and titanium oxides. The elemental homogeneity in the HEA nanoparticles could be improved by taking advantage of the HEO precursor with homogeneous elemental distributions, but the experimental results suggested the importance of the total reduction of oxide precursors to prepare homogeneous HEAs from HEOs.

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Leong, Zhaoyuan, Pratik Desai, and Nicola Morley. "Can Empirical Biplots Predict High Entropy Oxide Phases?" Journal of Composites Science 5, no. 12 (2021): 311. http://dx.doi.org/10.3390/jcs5120311.

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High entropy oxides are entropy-stabilised oxides that adopt specific disordered structures due to entropy stabilisation. They are a new class of materials that utilises the high-entropy concept first discovered in metallic alloys. They can have interesting properties due to the interactions at the electronic level and can be combined with other materials to make composite structures. The design of new meta-materials that utilise this concept to solve real-world problems may be a possibility but further understanding of how their phase stabilisation is required. In this work, biplots of the composition’s mean electronegativity are plotted against the electron-per-atom ratio of the compounds. The test dataset accuracy in the resulting biplots improves from 78% to 100% when using atomic-number-per-atom Z/a ratios as a biplot parameter. Phase stability maps were constructed using a Voronoi tessellation. This can be of use in determining stability at composite material interfaces.

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Bérardan, D., S. Franger, A. K. Meena, and N. Dragoe. "Room temperature lithium superionic conductivity in high entropy oxides." Journal of Materials Chemistry A 4, no. 24 (2016): 9536–41. http://dx.doi.org/10.1039/c6ta03249d.

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Impedance spectroscopy measurements evidence superionic Li+ mobility (>10−3 S cm−1) at room temperature and fast ionic mobility for Na+ (5 × 10−6 S cm−1) in high entropy oxides, a new family of oxide-based materials with the general formula (MgCoNiCuZn)1−x−yGayAxO (with A = Li, Na, K).

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Aziz, Saba, Anna Grazia Monteduro, Ritu Rawat, et al. "Preparation and Characterization of BXFO High-Entropy Oxides." Magnetochemistry 10, no. 8 (2024): 60. http://dx.doi.org/10.3390/magnetochemistry10080060.

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Increasing demand for functional materials crucial for advancing new technologies has motivated significant scientific and industrial research efforts. High-entropy materials (HEMs), with tunable properties, are gaining attention for their use in high-frequency transformers, microwave devices, multiferroics, and high-density magnetic memory components. The initial exploration of HEMs started with high-entropy alloys (HASs), such as CrMnFeCoNi, CuCoNiCrAlxFe, and AlCoCrTiZn and paved the way for a multitude of HEM variations, including oxides, oxyfluorides, borides, carbides, nitrides, sulfides, and phosphides. In this study, we fabricated the high-entropy oxide (HEO) compound Bi0.5La0.1In0.1Y0.1Nd0.1Gd0.1FeO3 through the solid-state synthesis method. Magnetic measurements at 300 K show ferromagnetic behavior with significant coercivity. At the same time, this novel composition exhibits excellent dielectric properties and shows potential for electronic applications demonstrating that a high-entropy approach can expand the compositional range of rare earth multiferroics and improve the multifunctional properties in multiferroic applications.

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Deng, Chang, Peiwen Wu, Linhua Zhu, et al. "High-entropy oxide stabilized molybdenum oxide via high temperature for deep oxidative desulfurization." Applied Materials Today 20 (September 2020): 100680. http://dx.doi.org/10.1016/j.apmt.2020.100680.

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Roy, Indranil, Pratik K. Ray, and Ganesh Balasubramanian. "Modeling Oxidation of AlCoCrFeNi High-Entropy Alloy Using Stochastic Cellular Automata." Entropy 24, no. 9 (2022): 1263. http://dx.doi.org/10.3390/e24091263.

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Together with the thermodynamics and kinetics, the complex microstructure of high-entropy alloys (HEAs) exerts a significant influence on the associated oxidation mechanisms in these concentrated solid solutions. To describe the surface oxidation in AlCoCrFeNi HEA, we employed a stochastic cellular automata model that replicates the mesoscale structures that form. The model benefits from diffusion coefficients of the principal elements through the native oxides predicted by using molecular simulations. Through our examination of the oxidation behavior as a function of the alloy composition, we corroborated that the oxide scale growth is a function of the complex chemistry and resultant microstructures. The effect of heat treatment on these alloys is also simulated by using reconstructed experimental micrographs. When they are in a single-crystal structure, no segregation is noted for α-Al2O3 and Cr2O3, which are the primary scale-forming oxides. However, a coexistent separation between Al2O3 and Cr2O3 oxide scales with the Al-Ni- and Cr-Fe-rich regions is predicted when phase-separated microstructures are incorporated into the model.

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Pikalova, Elena Y., Elena G. Kalinina, Nadezhda S. Pikalova, and Elena A. Filonova. "High-Entropy Materials in SOFC Technology: Theoretical Foundations for Their Creation, Features of Synthesis, and Recent Achievements." Materials 15, no. 24 (2022): 8783. http://dx.doi.org/10.3390/ma15248783.

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In this review, recent achievements in the application of high-entropy alloys (HEAs) and high-entropy oxides (HEOs) in the technology of solid oxide fuel cells (SOFC) are discussed for the first time. The mechanisms of the stabilization of a high-entropy state in such materials, as well as the effect of structural and charge factors on the stability of the resulting homogeneous solid solution are performed. An introduction to the synthesis methods for HEAs and HEOs is given. The review highlights such advantages of high-entropy materials as high strength and the sluggish diffusion of components, which are promising for the use at the elevated temperatures, which are characteristic of SOFCs. Application of the medium- and high-entropy materials in the hydrocarbon-fueled SOFCs as protective layers for interconnectors and as anode components, caused by their high stability, are covered. High-entropy solid electrolytes are discussed in comparison with traditional electrolyte materials in terms of conductivity. High-entropy oxides are considered as prospective cathodes for SOFCs due to their superior electrochemical activity and long-term stability compared with the conventional perovskites. The present review also determines the prioritizing directions in the future development of high-entropy materials as electrolytes and electrodes for SOFCs operating in the intermediate and low temperature ranges.

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Edalati, Parisa, Qing Wang, Hadi Razavi-Khosroshahi, Masayoshi Fuji, Tatsumi Ishihara, and Kaveh Edalati. "Photocatalytic hydrogen evolution on a high-entropy oxide." Journal of Materials Chemistry A 8, no. 7 (2020): 3814–21. http://dx.doi.org/10.1039/c9ta12846h.

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Lin, Ling, Kai Wang, Raheleh Azmi, et al. "Mechanochemical synthesis: route to novel rock-salt-structured high-entropy oxides and oxyfluorides." Journal of Materials Science 55, no. 36 (2020): 16879–89. http://dx.doi.org/10.1007/s10853-020-05183-4.

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Abstract A facile mechanochemical reaction at ambient temperature was successfully applied to synthesize novel single-phase rock-salt-structured high-entropy oxides, containing five, six and seven metal elements in equiatomic amounts. This synthesis approach overcomes the limitations of the commonly known synthesis procedures, which would result in multiple-phase compounds. Redox-sensitive elements, such as Fe2+ and Mn2+, can now be considered. The corresponding single-phase Li-containing high-entropy oxyfluorides were obtained by introducing LiF into the lattice using the same strategy. All materials show single-phase rock-salt structures with lattice parameters depending on the incorporated ion sizes. Solid solution states result in high configurational entropies, and all elements appear homogenously distributed over the whole cationic and anionic sublattice. The straightforward synthesis technique, combined with utilized simple binary oxide precursors, paves the way for a multitude of novel high-entropy oxide and oxyfluoride compounds. The compounds were studied by means of X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy and Mössbauer spectroscopy.

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Arshad, Muhammad, Saira Bano, Mohamed Amer, Vit Janik, Qamar Hayat, and Mingwen Bai. "High-Temperature Oxidation and Phase Stability of AlCrCoFeNi High Entropy Alloy: Insights from In Situ HT-XRD and Thermodynamic Calculations." Materials 17, no. 14 (2024): 3579. http://dx.doi.org/10.3390/ma17143579.

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The high-temperature oxidation behaviour and phase stability of equi-atomic high entropy AlCrCoFeNi alloy (HEA) were studied using in situ high-temperature X-ray diffraction (HTXRD) combined with ThermoCalc thermodynamic calculation. HTXRD analyses reveal the formation of B2, BCC, Sigma and FCC, phases at different temperatures, with significant phase transitions observed at intermediate temperatures from 600 °C–100 °C. ThermoCalc predicted phase diagram closely matched with in situ HTXRD findings highlighting minor differences in phase transformation temperature. ThermoCalc predictions of oxides provide insights into the formation of stable oxide phases, predominantly spinel-type oxides, at high p(O2), while a lower volume of halite was predicted, and minor increase observed with increasing temperature. The oxidation behaviour was strongly dependent on the environment, with the vacuum condition favouring the formation of a thin, Al2O3 protective layer, while in atmospheric conditions a thick, double-layered oxide scale of Al2O3 and Cr2O3 formed. The formation of oxide scale was determined by selective oxidation of Al and Cr, as further confirmed by EDX analysis. The formation of thick oxide in air environment resulted in a thick layer of Al-depleted FFC phase. This comprehensive study explains the high-temperature phase stability and time–temperature-dependent oxidation mechanisms of AlCrCoFeNi HEA. The interplay between surface phase transformation beneath oxide scale and oxides is also detailed herein, contributing to further development and optimisation of HEA for high temperature applications.

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Chen, Tianhui, Zhijiang Bi, Ji Zhou, et al. "Oxidation Behavior of Lightweight Al0.2CrNbTiV High Entropy Alloy Coating Deposited by High-Speed Laser Cladding." Coatings 14, no. 9 (2024): 1104. http://dx.doi.org/10.3390/coatings14091104.

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High-temperature oxidation resistance is the major influence on the high-temperature service stability of refractory high entropy alloys. The oxidation behavior of lightweight Al0.2CrNbTiV refractory high entropy alloy coatings with different dilution ratios at 650 °C and 800 °C deposited by high-speed laser cladding was analyzed in this paper. The oxidation kinetic was analyzed, the oxidation resistance mechanism of the Al0.2CrNbTiV coating was clarified with the analysis of the formation and evolution of the oxidation layer, and the effect of the dilution rate on high-temperature performances was revealed. The results showed that the oxide layer was mainly composed of rutile oxides (Ti, Cr, Nb)O2 after isothermal oxidation at 650 °C and 800 °C for 50 h. The Al0.2CrNbTiV coating in low dilution exhibited better oxidation performance at 650 °C, due to the dense oxide layer formed with the synergistic growth of fine AlVO3 particles and (Ti, Cr, Nb)O2, and higher percentage of Cr, Nb in (Ti, Cr, Nb)O2 strengthened the lattice distortion effect to inhibit the penetration of oxygen. The oxide layer formed at 800 °C for the Al0.2CrNbTiV coating was relatively loose, but the oxidation performance of the coating in high dilution improved due to the precipitation of Cr2Nb-type Laves phases along grain boundaries, which inhibits the diffusion of oxygen.

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35

Yurchenko, Nikita, Evgeniya Panina, Sergey Zherebtsov, Gennady Salishchev, and Nikita Stepanov. "Oxidation Behavior of Refractory AlNbTiVZr0.25 High-Entropy Alloy." Materials 11, no. 12 (2018): 2526. http://dx.doi.org/10.3390/ma11122526.

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Oxidation behavior of a refractory AlNbTiVZr0.25 high-entropy alloy at 600–900 °C was investigated. At 600–700 °C, two-stage oxidation kinetics was found: Nearly parabolic oxidation (n = 0.46–0.48) at the first stage, transitioned to breakaway oxidation (n = 0.75–0.72) at the second stage. At 800 °C, the oxidation kinetics was nearly linear (n = 0.92) throughout the entire duration of testing. At 900 °C, the specimen disintegrated after 50 h of testing. The specific mass gains were estimated to be 7.2, 38.1, and 107.5, and 225.5 mg/cm2 at 600, 700, and 800 °C for 100 h, and 900 °C for 50 h, respectively. Phase compositions and morphology of the oxide scales were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was shown that the surface layer at 600 °C consisted of the V2O5, VO2, TiO2, Nb2O5, and TiNb2O7 oxides. Meanwhile, the scale at 900 °C comprised of complex TiNb2O7, AlNbO4, and Nb2Zr6O17 oxides. The oxidation mechanisms operating at different temperatures were discussed and a comparison of oxidation characteristics with the other alloys was conducted.

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Csík, D., D. Zalka, K. Saksl, D. Capková, and R. Džunda. "Four-component high entropy spinel oxide as anode material in lithium-ion batteries with excellent cyclability." Journal of Physics: Conference Series 2382, no. 1 (2022): 012003. http://dx.doi.org/10.1088/1742-6596/2382/1/012003.

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Nowadays, energy storage technologies are in focus of public interest, especially in the field of the automotive industry. Lithium-ion batteries (LIBs) are evaluated as one of the most advanced energy storage devices because of their high energy density, which can meet rapidly growing energy requirements. Graphite based anode materials in LIBs are reaching their fundamental limits, especially their specific capacities. Recently, it has been demonstrated that high entropy oxides (HEOs) possess promising and unexpected electrochemical properties, such as remarkable reversible capacity and cycle stability due to the high entropy of the system. The highly disordered structure can provide self-healing properties resulting in regeneration of the capacity by applying low current densities. In addition, they can alleviate volume changes during the cycling process, unlike simple oxides. Among the various types of high entropy oxides, spinel-structured HEOs are the most studied because they ensure the three-dimensional transport of lithium ions ensuring high rate capability. Herein, we report a simple method of preparation of high entropy oxide (HEO) with a spinel structure consisting of 4 different elements (Co, Fe, Cr, Ni). The prepared HEO exhibited excellent cycle stability during (116 mAh.g-1) 500 cycles at a current density of 500 mA.g-1, which confirms their usage as anode active materials in lithium-ion batteries.

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Zaitseva, O. V., D. A. Vinnik, and Evgeny A. Trofimov. "The Poly-Substituted M-Type Hexaferrite Crystals Growth." Materials Science Forum 946 (February 2019): 186–91. http://dx.doi.org/10.4028/www.scientific.net/msf.946.186.

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In the presented article the possibility analysis of highly entropic oxide phases composition and structure formation was performed. Moreover, the studies devoted to the production of substituted single crystals with the M-type hexa-ferrite structure were carried out. The experiments were conducted to studying the possibility of obtaining oxide high-entropy crystalline solid solutions with the M-type hexa-ferrites structure. As the result of the crystallized samples investigation, the microcrystalline highly entropic Ba (Fe,Mn,Ni,Ti,Al)12O19 and (Ba,Pb,Sr)(Fe,Mn,Ti,Ni,Al)12O19 phases appearing was detected. Based on the obtained data, it is possible to consider that the poly-substituted crystals growth with M-type hexa-ferrite structure. The structural stabilization is promoted by high values of the configurational entropy of the crystal matrix components mixing.

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38

Guo, Hui-Xia, Wei-Ming Wang, Cheng-Yu He, et al. "Entropy-Assisted High-Entropy Oxide with a Spinel Structure toward High-Temperature Infrared Radiation Materials." ACS Applied Materials & Interfaces 14, no. 1 (2021): 1950–60. http://dx.doi.org/10.1021/acsami.1c20055.

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Sun, Zheng, Yongjie Zhao, Chen Sun, Qing Ni, Chengzhi Wang, and Haibo Jin. "High entropy spinel-structure oxide for electrochemical application." Chemical Engineering Journal 431 (March 2022): 133448. http://dx.doi.org/10.1016/j.cej.2021.133448.

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Phakatkar, Abhijit, Reza Shahbazian-Yassar, and Tolou Shokuhfar. "STEM-EELS Analysis of High Entropy Oxide Nanoparticles." Microscopy and Microanalysis 27, S1 (2021): 884–86. http://dx.doi.org/10.1017/s1431927621003421.

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Shi, Yunzhu, Rui Li, and Zhifeng Lei. "Influences of Synthetic Parameters on Morphology and Growth of High Entropy Oxide Nanotube Arrays." Coatings 13, no. 1 (2022): 46. http://dx.doi.org/10.3390/coatings13010046.

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Nanoscale and nanostructured materials have drawn great attention owing to their outstanding and unique properties. Enlightened by the study of “entropy-stabilized oxides”, nanotubes consisting of multi-component mixed metal oxides are developed, which formed on equi-atomic TiZrHfNbTa high-entropy alloy (HEA). However, the growth mechanism and how the oxidation conditions influence the nanotube growth and morphology remains unknown. In the present study, by controlling the anodization parameters (applied voltages and time) and bath compositions (fluoride concentration and water content), scanning electron microscope and transmission electron microscopy are conducted to reveal the morphological evolution. The present work uncovers how the synthetic parameters influence the tube growth and morphology formed on equi-atomic TiZrHfNbTa HEA, therefore gaining insight into the growth mechanism and the feasibility of controlling the morphology of multi-component oxide nanotubes.

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Jiang, Ji Chao, and Xiu Yan Luo. "High Temperature Oxidation Behaviour of AlCuTiFeNiCr High-Entropy Alloy." Advanced Materials Research 652-654 (January 2013): 1115–18. http://dx.doi.org/10.4028/www.scientific.net/amr.652-654.1115.

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The oxidation behaviour of AlCuTiFeNiCr high-entropy alloy with was studied at 850 oC in atmosphere. The oxide layer of long-term oxidation behavior were examined using optical, X-ray powder diffraction (XRD) with the aid of scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis (EDX). The oxidation kinetics follows a parabolic rate law. The oxidation rate decreases gradually as the oxidation proceeds.

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Liu, Bu-Jine, Tai-Hsin Yin, Yu-Wei Lin, et al. "A Cost-Effective, Nanoporous, High-Entropy Oxide Electrode for Electrocatalytic Water Splitting." Coatings 13, no. 8 (2023): 1461. http://dx.doi.org/10.3390/coatings13081461.

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High-entropy materials have attracted extensive attention as emerging electrode materials in various energy applications due to their flexible tunability, unusual outstanding activities, and cost-effectiveness using multiple earth-abundant elements. We introduce a novel high-entropy composite oxide with the five elements of Cu, Ni, Co, Fe, and Cr (HEO-3CNF) for use in the oxygen evolution reaction (OER) in electrocatalytic water splitting. HEO-3CNF is composed of two phases with a non-equimolar, deficient high-entropy spinel oxide of (Cu0.2−xNi0.2Co0.2Fe0.2Cr0.2)3O4 and monoclinic copper oxide (CuO). Electrochemical impedance spectroscopy (EIS) with distribution of relaxation times (DRT) analysis validates that the HEO-3CNF-based electrode exhibits faster charge transfer than benchmark CuO. It results in improved OER performance with a lower overpotential at 10 mA/cm2 and a Tafel slope than CuO (518.1 mV and 119.7 mV/dec versus 615.9 mV and 131.7 mV/dec, respectively) in alkaline conditions. This work may provide a general strategy for preparing novel, cost-effective, high-entropy electrodes for water splitting.

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Lo Faro, Massimiliano, and Sebastian Vecino-Mantilla. "High-Entropy Proton Conductive Electrolyte for Intermediate Temperature Operation." ECS Transactions 111, no. 6 (2023): 1817–21. http://dx.doi.org/10.1149/11106.1817ecst.

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Due to the high operating temperatures required by commercially available cells, solid oxide electrochemical devices are currently limited in their application to sectors ranging from production to storage of energy, from pollution abatement to pure oxygen distillation. In this study, it is presented a novel electrolyte that promises to dramatically reduce the operating temperature of solid oxide electrochemical devices. Our proposed electrolyte consists of four cations and non-critical raw materials with a stoichiometry that allows for maximum entropy in an ABO3-based oxide. Preliminary results presented in this proceeding indicate that the material outperforms commercial cerates and zirconates in terms of thermal and electrochemical properties, while there is still room for further improvements.

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Korda, Akhmad Ardian, Mohamad Ali Akbar, Fadhli Muhammad, et al. "High-Temperature Oxidation and Microstructural Changes of Al0.75CoCrFeNi High-Entropy Alloy at 900 and 1100 °C." Metals 14, no. 1 (2023): 33. http://dx.doi.org/10.3390/met14010033.

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The development of high-entropy alloys (HEAs) for high-temperature applications has been driven by the limitation of nickel-based superalloys in achieving optimal efficiency at higher temperatures for higher efficiency in power generation engines. The alloys must have high oxidation resistance and microstructural stability at high temperatures. Relatively equimolar multi elements involved in HEAs produce microstructure containing a single solid solution or multiphase that improves the mechanical properties and oxidation resistance resulting from sluggish diffusion and core effects. In this study, the oxidation behavior and microstructural changes of Al0.75CoCrFeNi HEA at 900, 1000, and 1100 °C in air atmosphere were investigated. Based on the XRD and SEM-EDS analysis, the mechanism of oxide scale formation and microstructural changes of the substrate are proposed. The results show that the oxidation behavior of the alloy follows a logarithmic rate law. Different oxide compounds of CoO, NiO, Cr2O3, and CrO3, θ-Al2O3, α-Al2O3, and Ni(Cr,Al)2O4 with semicontinuous oxides of Al2O3 with Cr2O3 subscale and an oxide mixture consisting of spinel of Ni(Cr,Al)2O4 and Co(Cr,Al)2O4 were found. During oxidation, Widmanstätten of FCC-A1 and BCC-B2/A2 phases in the substrate have changed. Spheroidization of B2 and a reduction in volume fraction decrease the hardness of the substrates.

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Tatar, Dalibor, Jelena Kojčinović, Berislav Marković, et al. "Sol-Gel Synthesis of Ceria-Zirconia-Based High-Entropy Oxides as High-Promotion Catalysts for the Synthesis of 1,2-Diketones from Aldehyde." Molecules 26, no. 20 (2021): 6115. http://dx.doi.org/10.3390/molecules26206115.

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Efficient Lewis-acid-catalyzed direct conversion of aldehydes to 1,2-diketones in the liquid phase was enabled by using newly designed and developed ceria–zirconia-based high-entropy oxides (HEOs) as the actual catalysts. The synergistic effect of various cations incorporated in the same oxide structure (framework) was partially responsible for the efficiency of multicationic materials compared to the corresponding single-cation oxide forms. Furthermore, a clear, linear relationship between the Lewis acidity and the catalytic activity of the HEOs was observed. Due to the developed strategy, exclusively diketone-selective, recyclable, versatile heterogeneous catalytic transformation of aldehydes can be realized under mild reaction conditions.

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Samoilova, O. V., N. A. Shaburova, M. V. Sudarikov, and E. A. Trofimov. "High-temperature oxidation resistance of Al0.25CoCrFeNiSi0.6 high entropy alloy." Ferrous Metallurgy. Bulletin of Scientific , Technical and Economic Information 78, no. 11 (2023): 978–86. http://dx.doi.org/10.32339/0135-5910-2022-11-978-986.

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High entropy alloys (HEAs) are a relatively new type of alloys and, unlike traditional alloys based on one or two main components, HEAs include five or more components in close to equimolar ratios. These alloys are currently considered as promising materials for the manufacture of coatings on parts operating in difficult operating conditions – parts of gas turbines, turbojet and jet engines, etc. The possible use of HEAs at high temperatures makes it relevant to assess the ability of HEAs to resist high-temperature oxidation. In the course of this work, the behavior of the HEA of the composition Al0.25CoCrFeNiSi0.6 was studied during isothermal exposure for 10 hours for temperatures of 700 and 1000 °C in air. The kinetic curves of oxidation were constructed, on the basis of which it was established that the spe-cific weight gain after 10 hours of exposure at 700 °C was 1 mg/cm2, at 1000 °C – 4 mg/cm2. Samples before and after oxidation were studied using scanning electron microscopy, X-ray spectral microanalysis, and X-ray phase analysis. It has been established that the phase composition of the oxide film after exposure at 700 °C is represented only by Al2O3 and Cr2O3 oxides, while after exposure at 1000 °C were found Al2O3, Cr2O3, SiO2, Al2SiO5, Fe2SiO4, Fe3O4, CoFe2O4 and FeCr2O4. The use of the Al0.25CoCrFeNiSi0.6 HEA with the ratio Si/Al = 2.4 under operating conditions at elevated temperatures can be considered inappropriate.

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Webb, Matthew, Mike Gerhart, Steven Baksa, et al. "High temperature stability of entropy-stabilized oxide (MgCoNiCuZn)0.2O in air." Applied Physics Letters 124, no. 15 (2024). http://dx.doi.org/10.1063/5.0199076.

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Entropy-stabilized oxides are single-phase, multicomponent oxides that are stabilized by a large entropy of mixing, ΔS, overcoming a positive enthalpy. Due to the −TΔS term in the Gibbs' free energy, G, it can be hypothesized that entropy-stabilized oxides demonstrate a robust thermal stability. Here, we investigate the high temperature stability (1300–1700 °C) of the prototypical entropy-stabilized rocksalt oxide (MgCoNiCuZn)0.2O in air. We find that at temperatures &gt;1300 °C, the material gradually loses Cu and Zn with increasing temperature. Cu is lost through a selective melting as a Cu-rich liquid phase is formed. Zn is sublimed from the rocksalt phase at approximately similar temperatures to those corresponding to the Cu loss, significantly below both the melting temperature of ZnO and its solubility limit in a rocksalt phase. The elemental loss progressively reduces the entropy of mixing and results in a multiphase solid upon quenching to room temperature. We posit that the high-temperature solubility of Cu and Zn is correlated providing further evidence for entropic stabilization over general solubility arguments.

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Liu, Yifan, Caichao Ye, Long Chen, et al. "High Entropy‐Driven Role of Oxygen Vacancies for Water Oxidation." Advanced Functional Materials, January 30, 2024. http://dx.doi.org/10.1002/adfm.202314820.

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AbstractOxygen vacancy engineering is a promising strategy to enhance the electrocatalytic activities in conventional metal oxide electrocatalysts. However, the utilization of oxygen vacancies in high‐entropy oxides remains unknown, primarily due to the challenges associated with facile introduction of the oxygen vacancies and explanation of their roles in complex high‐entropy systems. Herein, the facile introduction of oxygen vacancies into high‐entropy oxides is realized and the unique high entropy‐driven role of oxygen vacancies for oxygen evolution reaction (OER) process is revealed. A low‐temperature surface carbonization–decarbonization approach is developed to introduce and regulate the oxygen vacancies in high‐entropy spinel oxides (HEOs). The oxygen vacancies in HEOs can both facilitate pre‐oxidation process for faster OH− adsorption and induce the unique bridge site pathway for easier deprotonation, distinctive in conventional oxides where oxygen vacancies favor *OH adsorption yet hinder the deprotonation. Consequently, the as‐prepared high‐entropy spinel oxides with oxygen vacancies (HEOs‐Ov) exhibit superior OER activities, outperforming the HEOs and most reported oxide‐based electrocatalysts. Besides, this universal method can be extended to other spinel oxides with different configuration entropies and can be scaled up. The work paves the way for the exploration of oxygen vacancies in high‐entropy oxides toward electrocatalysis fields.

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Jana, Subhra Sourav, and Tanmoy Maiti. "Designing Rare Earth Free High Entropy Oxide with Tungsten Bronze Structure for Thermoelectric Application." Materials Horizons, 2023. http://dx.doi.org/10.1039/d2mh01488b.

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In the recent years, forming high entropy oxides has emerged as one of the promising approaches to design oxide thermoelectrics. Entropy engineering is an excellent strategy to improve thermoelectric performance...

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Journal articles on the topic 'High entropy oxide'

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