Defect structure and transport properties in (Co,Cu,Mg,Ni,Zn)O high entropy oxide

Grzesik, Z.; Smoła, G.; Stygar, Mirosław; Dąbrowa, Juliusz; Zajusz, Marek; Mroczka, K.; Danielewski, Marek

doi:10.1016/j.jeurceramsoc.2019.06.018

Cited by 58 publications

(27 citation statements)

References 25 publications

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“…It can be seen that the average stress per atom for the Cu cation change from tensile to compresssive state at oxygen vacancy concentration of 0.056‐0.067. Also, reported in literature the maximum oxygen vacancy concentration is 0.07 for this particular composition of ESO . In order to create 0.056‐0.067 oxygen vacancy concentration it was required that 0.65‐0.75 wt% of oxygen was removed from the lattice.…”

Section: Resultsmentioning

confidence: 86%

“…30 The presence of oxygen vacancies in the 5C stabilized single-phase lattice was further validated by a recent report. 31 We believe that the creation of oxygen vacancies is a result of quenching the sample from a higher temperature. Therefore, in order to understand the role of Cu 2+ ions and oxygen vacancies in stabilization of lattice to a single phase, molecular dynamics (MD) simulation was used.…”

Section: Simulation Detailsmentioning

confidence: 98%

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Critical role of cationic local stresses on the stabilization of entropy‐stabilized transition metal oxides

2020

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Entropy‐stabilized transition metal oxides ([MgNiCoCuZn]O) (ESO) in recent years have received considerable attention owing to their unique functional properties. Solution combustion and solid state syntheses resulted in crystallites varying from 5‐15 nm to 3‐5 μm respectively. Phase stability studies showed that all the systems containing Cu2+ ions in the ESO lattice segregated upon slow cooling in the furnace. It was only when ESO was quenched in air from 1000°C the lattice stabilized to a single phase. Experiments concomitant with molecular dynamics (MD) simulations demonstrated that the local stress fields around the cations played a critical role in stabilizing the single phase. The local stress fields are a result of Jahn‐Teller distortion induced by the Cu2+ ions in the lattice. It is clearly established that in the absence of the minimization of the local stress fields around the Cu2+ ions, segregation leading to the formation of a multi‐phase material is imminent for this particular composition.

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Section: Resultsmentioning

confidence: 86%

Section: Simulation Detailsmentioning

confidence: 98%

Critical role of cationic local stresses on the stabilization of entropy‐stabilized transition metal oxides

2020

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“…To the best of our knowledge, all of the previously reported single‐phase high‐entropy oxide ceramics synthesized using conventional solid‐state reaction were subjected to fast cooling, such as air quenching or rapid cooling by turning off the furnace, which is common for high‐entropy materials in order to preserve the entropy‐stabilized phases that are favorably formed at high temperatures …”

Section: Introductionmentioning

confidence: 99%

“…Recently the high-entropy concept has been extended to metal diborides 17 carbides 18 nitrides, 19 and oxides. 20 The field of high-entropy oxides attracts attention as a current research topic, [21][22][23][24][25][26] particularly due to the functional properties that have been reported, such as high dielectric constant, 27 lithium superionic conductivity, 28 magnetic properties, [29][30][31] electrical and thermal conductivities, 32,33 reversible energy storage, 34 and high catalytic activity in CO oxidation. 35 Launching the field of high-entropy oxides, Rost 20 reported a single rocksalt structure for (Mg ,Ni, Co, Cu, Zn)O pellets produced using solid-state synthesis.…”

Section: Introductionmentioning

confidence: 99%

“…To the best of our knowledge, all of the previously reported single-phase high-entropy oxide ceramics synthesized using conventional solid-state reaction were subjected to fast cooling, such as air quenching or rapid cooling by turning off the furnace, 20,[25][26][27]33,[43][44][45] which is common for high-entropy materials in order to preserve the entropy-stabilized phases that are favorably formed at high temperatures. 3 The purpose of this work was to investigate the effects of composition, sintering atmosphere, and cooling rate on T A B L E 1 Ionic radii correlated to coordination number, crystal structure, and oxidation state of rare-earth cations in dioxides and sesquioxides 40,41 the production of single-phase multicomponent rare-earth oxides using solid-state synthesis.…”

Section: Introductionmentioning

confidence: 99%

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Solid‐state synthesis of multicomponent equiatomic rare‐earth oxides

et al. 2020

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Phase formation in multicomponent rare-earth oxides is determined by a combination of composition, sintering atmosphere, and cooling rate. Polycrystalline ceramics comprising various combinations of Ce, Gd, La, Nd, Pr, Sm, and Y oxides in equiatomic proportions were synthesized using solid-state sintering. The effects of composition, sintering atmosphere, and cooling rate on phase formation were investigated. Single cubic or monoclinic structures were obtained with a slow cooling of 3.3°C/min, confirming that rare-earth oxides follow a different structure stabilization process than transition metal high-entropy oxides. In an oxidizing atmosphere, both Ce and Pr induce a cubic structure, while only Ce plays that role in an inert or reducing atmosphere. Samples without Ce or Pr develop a single monoclinic structure. The structures formed at initial synthesis may be converted to a different one, when the ceramics are annealed in an additional atmosphere. Phase evolution of a five-cation composition was also studied as a function of sintering temperature. The binary oxides used as raw materials completely dissolve into a single cubic structure at 1450°C in air. K E Y W O R D S phase transformations, rare earths, reaction sintering How to cite this article: Pianassola M, Loveday M, McMurray JW, Koschan M, Melcher CL, Zhuravleva M. Solid-state synthesis of multicomponent equiatomic rare-earth oxides. J Am Ceram Soc.

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Reversible Enhancement of Electronic Conduction Caused by Phase Transformation and Interfacial Segregation in an Entropy‐Stabilized Oxide

Vahidi,

Dupuy,

Lam

et al. 2024

Adv Funct Materials

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Entropy‐stabilized oxide (ESO) research has primarily focused on discovering unprecedented structures, chemistries, and properties in the single‐phase state. However, few studies discuss the impacts of entropy stabilization and secondary phases on functionality and in particular, electrical conductivity. To address this gap, electrical transport mechanisms in the canonical ESO rocksalt (Co,Cu,Mg,Ni,Zn)O are assessed as a function of secondary phase content. When single‐phase, the oxide conducts electrons via Cu+/Cu2+ small polarons. After 2 h of heat treatment, Cu‐rich tenorite secondary phases form at some grain boundaries (GBs), enhancing grain interior electronic conductivity by tuning defect chemistry toward higher Cu+ carrier concentrations. 24 h of heat treatment yields Cu‐rich tenorite at all GBs, followed by the formation of anisotropic Cu‐rich tenorite and equiaxed Co‐rich spinel secondary phases in grains, further enhancing grain interior electronic conductivity but slowing electronic transport across the tenorite‐rich GBs. Across all samples, the total electrical conductivity increases (and decreases reversibly) by four orders of magnitude with heat‐treatment‐induced phase transformation by tuning the grains’ defect chemistry toward higher carrier concentration and lower migration activation energy. This work demonstrates the potential to selectively grow secondary phases in ESO grains and at GBs, thereby tuning the electrical properties using microstructure design, nanoscale engineering, and heat treatment, paving the way to develop many novel materials.

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Defect structure and transport properties in (Co,Cu,Mg,Ni,Zn)O high entropy oxide

Cited by 58 publications

References 25 publications

Critical role of cationic local stresses on the stabilization of entropy‐stabilized transition metal oxides

Critical role of cationic local stresses on the stabilization of entropy‐stabilized transition metal oxides

Solid‐state synthesis of multicomponent equiatomic rare‐earth oxides

Reversible Enhancement of Electronic Conduction Caused by Phase Transformation and Interfacial Segregation in an Entropy‐Stabilized Oxide

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