High Configurational Entropy Research Articles

High-entropy assisted BaTiO3-based ceramic capacitors for energy storage

The market-dominating material BaTiO 3 is highly crucial in advanced electronics and electric power systems owing to its fast charging/discharging speed and superior cycle life. However, the low energy storage efficiency and breakdown strength hinder further device miniaturization for energy storage applications. Herein, we design a high configurational entropy (HCE) material BaTiO 3 -BiFeO 3 -CaTiO 3 with rational microstructural engineering that demonstrates an ultrahigh energy density of 7.2 J cm −3 . The HCE design leads to the increased solubility of CaTiO 3 in the matrix, which enhances the resistivity and polarization. Simultaneously, the nano-segregations around the grains can enhance the breakdown strength obviously due to strongly scattering of electron carriers and impeding of electrical breakdown pathways. Furthermore, the multilayer ceramic capacitors (MLCCs) using such dielectrics were constructed with energy density of 16.6 J cm −3 and efficiency of 83%. This work offers a route to explore new dielectric materials that are expected to benefit dielectric devices' compactness and high performance. • High-entropy relaxor-ferroelectric is designed and synthesized • Special microstructure related to the improvement of electric breakdown strength • High energy storage density of 16.6 Jcm −3 is achieved in the MLCC Qi et al. report a high-entropy relaxor-ferroelectric material BaTiO 3 -BiFeO 3 -CaTiO 3 with rational microstructural engineering. They achieve an ultrahigh energy density of 16.6 J cm −3 , and efficiency of 83% in a prototype MLCC device.

New class of high-entropy pseudobrookite titanate with excellent thermal stability, low thermal expansion coefficient, and low thermal conductivity

As a type of titanate, the pseudobrookite (MTi2O5/M2TiO5) exhibits a low thermal expansion coefficient and thermal conductivity, as well as excellent dielectric and solar spectrum absorption properties. However, the pseudobrookite is unstable and prone to decomposing below 1200 °C, which limits the practical application of the pseudobrookite. In this paper, the high-entropy pseudobrookite ceramic is synthesized for the first time. The pure high-entropy (Mg,Co,Ni,Zn)Ti2O5 with the pseudobrookite structure and the biphasic high-entropy ceramic composed of the high-entropy pseudobrookite (Cr,Mn,Fe,Al,Ga)2TiO5 and the high-entropy spinel (Cr,Mn,Fe,Al,Ga,Ti)3O4 are successfully prepared by the in-situ solid-phase reaction method. The comparison between the theoretical crystal structure of the pseudobrookite and the aberration-corrected scanning transmission electron microscopy (AC-STEM) images of high-entropy (Mg,Co,Ni,Zn)Ti2O5 shows that the metal ions (M and Ti ions) are disorderly distributed at the A site and the B site in high-entropy (Mg,Co,Ni,Zn)Ti2O5, leading to an unprecedentedly high configurational entropy of high-entropy (Mg,Co,Ni,Zn)Ti2O5. The bulk high-entropy (Mg,Co,Ni,Zn)Ti2O5 ceramics exhibit a low thermal expansion coefficient of 6.35×10−6 K−1 in the temperature range of 25–1400 °C and thermal conductivity of 1.840 W·m−1·K−1 at room temperature, as well as the excellent thermal stability at 200, 600, and 1400 °C. Owing to these outstanding properties, high-entropy (Mg,Co,Ni,Zn)Ti2O5 is expected to be the promising candidate for high-temperature thermal insulation. This work has further extended the family of different crystal structures of high-entropy ceramics reported to date.

Regulating the Configurational Entropy to Improve the Thermoelectric Properties of (GeTe)1-x(MnZnCdTe3)x Alloys.

In thermoelectrics, entropy engineering as an emerging paradigm-shifting strategy can simultaneously enhance the crystal symmetry, increase the solubility limit of specific elements, and reduce the lattice thermal conductivity. However, the severe lattice distortion in high-entropy materials blocks the carrier transport and hence results in an extremely low carrier mobility. Herein, the design principle for selecting alloying species is introduced as an effective strategy to compensate for the deterioration of carrier mobility in GeTe-based alloys. It demonstrates that high configurational entropy via progressive MnZnCdTe3 and Sb co-alloying can promote the rhombohedral-cubic phase transition temperature toward room temperature, which thus contributes to the enhanced density-of-states effective mass. Combined with the reduced carrier concentration via the suppressed Ge vacancies by high-entropy effect and Sb donor doping, a large Seebeck coefficient is attained. Meanwhile, the severe lattice distortions and micron-sized Zn0.6Cd0.4Te precipitations restrain the lattice thermal conductivity approaching to the theoretical minimum value. Finally, the maximum zT of Ge0.82Sb0.08Te0.90(MnZnCdTe3)0.10 reaches 1.24 at 723 K via the trade-off between the degraded carrier mobility and the improved Seebeck coefficient, as well as the depressed lattice thermal conductivity. These results provide a reference for the implementation of entropy engineering in GeTe and other thermoelectric materials.

Entropy engineering enhances the thermoelectric performance and microhardness of (GeTe)1−x(AgSb0.5Bi0.5Te2)x

As an endogenous material genetic property, entropy is an emerging fingerprint factor in the material genome. By designing multicomponent thermoelectric materials with high configuration entropy, the lattice thermal conductivity can be significantly reduced via severe lattice distortion, and the Seebeck coefficient can be improved by enhancing the crystal symmetry. However, high entropy also causes the deterioration of carrier mobility, restraining the improvement of the dimensionless figure of merit zT. Herein, we design the (GeTe)1−x(AgSb0.5Bi0.5Te2)x, aka TABGS alloys, via replacing half of the Sb by Bi in the well-known (GeTe)1−x-(AgSbTe2)x, aka TAGS alloys, to attest the efficacy of entropy engineering. In view of the low carrier mean free path of TAGS alloys approaching to the Mott-Ioffe-Regel limit, further Bi substitution and increased configuration entropy cannot impair the carrier mobility any longer. In addition, the suppressed rhombohedral-cubic phase transition via high configuration entropy and the reduced carrier concentration contribute to the substantially improved Seebeck coefficient. Furthermore, the elicited multiscale microstructures and the decreased sound velocity upon AgSb0.5Bi0.5Te2 alloying effectively restrain the lattice thermal conductivity. As a result, (GeTe)0.80(AgSb0.5Bi0.5Te2)0.20 achieves a high zT of 1.60 at 723 K and an average zTave of 1.23 from 300 to 773 K. Meantime, its room-temperature Vickers hardness reaches 2.21 GPa due to solid solution hardening. These results highlight the efficacy of entropy engineering in enhancing the thermoelectric performance, especially for numerous materials with intrinsically low carrier mobility.

Manufacturing of Ti-Nb-Cr-V-Ni-Al Refractory High-Entropy Alloys Using Direct Energy Deposition.

High-entropy alloys (HEAs) are composed of 5–35 at% of five or more elements, have high configurational entropy, do not form intermetallic compounds, and have a single-phase face-centered cubic structure or body-centered cubic structure. In particular, refractory HEAs (RHEAs), based on refractory materials with excellent mechanical properties at high temperatures, have high strength and hardness at room temperature and excellent mechanical properties at low and high temperatures. In this study, the Ti-Nb-Cr-V-Ni-Al RHEAs were deposited using direct energy deposition (DED). In the microstructure of Ti-Nb-Cr-V-Ni-Al, the sigma, BCC A2, and Ti2Ni phases appeared to be different from the BCC A2, BCC B2, and Laves phases predicted in the phase diagram. This microstructure was similar to that of the casted Ti-Nb-Cr-V-Ni-Al and had a constructed fine grain size. It was found that the growth of these microstructures was due to the DED process, which has a fast solidification rate. The fine grain size caused high hardness, and the microhardness of the Ti-Nb-Cr-V-Ni-Al was measured to be about 900 HV. In addition, in order to analyze the thermal properties of Ti-Nb-Cr-V-Ni-Al composed of the refractory material, the heat-affected zone (HAZ) was analyzed through a preheating test. The HAZ was decreased, owing to the high thermal diffusivity of Ti-Nb-Cr-V-Ni-Al.

P2-type layered high-entropy oxides as sodium-ion cathode materials

P2-type layered oxides with the general Na-deficient composition Na x TMO2 (x < 1, TM: transition metal) are a promising class of cathode materials for sodium-ion batteries. The open Na+ transport pathways present in the structure lead to low diffusion barriers and enable high charge/discharge rates. However, a phase transition from P2 to O2 structure occurring above 4.2 V and metal dissolution at low potentials upon discharge results in rapid capacity degradation. In this work, we demonstrate the positive effect of configurational entropy on the stability of the crystal structure during battery operation. Three different compositions of layered P2-type oxides were synthesized by solid-state chemistry, Na0.67(Mn0.55Ni0.21Co0.24)O2, Na0.67(Mn0.45Ni0.18Co0.24Ti0.1Mg0.03)O2 and Na0.67(Mn0.45Ni0.18Co0.18Ti0.1Mg0.03Al0.04Fe0.02)O2 with low, medium and high configurational entropy, respectively. The high-entropy cathode material shows lower structural transformation and Mn dissolution upon cycling in a wide voltage range from 1.5 to 4.6 V. Advanced operando techniques and post-mortem analysis were used to probe the underlying reaction mechanism thoroughly. Overall, the high-entropy strategy is a promising route for improving the electrochemical performance of P2 layered oxide cathodes for advanced sodium-ion battery applications.

Cocktail effect on RT5-type (R = rare earth, T = 3d transition metal) high entropy intermetallic compounds

The alloys with normal compositions of (Sm1/2Ce1/2)(Co1/3Cu1/3Ni1/3)5, (Sm1/2Pr1/2)(Co1/3Cu1/3Ni1/3)5, (Sm1/2Nd1/2)(Co1/3Cu1/3Ni1/3)5, (Sm1/3Ce1/3Pr1/3)(Co1/3Cu1/3Ni1/3)5, and (Sm1/3Ce1/3Nd1/3)(Co1/3Cu1/3 Ni1/3)5 are designed by mixing RCo5, RNi5, and RCu5 for studying their cocktail effects. These designed alloys are prepared by vacuum Arc melting technology. Their single-phase characteristics are experimentally confirmed by X-ray diffraction and scanning electron microscope with energy dispersive spectrum, and also theoretically confirmed by the reported single-phase formation rule of high entropy alloys: atomic radius difference within 6%, nonpositive mixing enthalpy, and high configuration entropy above 1.50R. The designed alloys are suggested to be the high entropy intermetallic compounds due to their single-phase characteristics and high configuration entropy. The magnetic cocktail effect is observed in magnetic measurements. These intermetallic compounds show low-temperature magnetic transition and field-induced ferromagnetic characteristics. The cocktail effect is suggested to be modulated by the spins with random directions at rare earth and transition metal sublattices caused by mixture of the multiple individual RCo5, RNi5, and RCu5 intermetallic compounds.

High-entropy transition metal chalcogenides as electrocatalysts for renewable energy conversion

High-entropy transition metal chalcogenides (HE-TMCs) are advantageous in electrocatalytic applications compared to other entropy-stabilized systems owing to the greater orbital extension and energetic match of p-orbitals in chalcogenides with d-orbitals of the transition metals providing additional space to tailor their electronic structure. The high-configurational entropy of HE-TMCs leads to stabilization of cubic rock salt, wurtzite-type and hexagonally packed 2D structures. Due to the multi-element nature of HE-TMCs, the synergy among different elements results in tunable d- and p-band positions. As a consequence, the adsorption energies of electrocatalytic reaction intermediates can be tailored to enhance catalytic performance in water splitting and CO2 reduction. Furthermore, the entropy-stabilized disordered microstructural state of the material endows HE-TMCs with improved corrosion resistance. Despite recent advances in HE-TMC electrocatalysis, challenges such as identification and synthesis of efficient HE-TMCs as well as the identification of catalytically active sites and reaction mechanisms on HE-TMCs remain to be investigated.

Visible-light photocatalytic oxygen production on a high-entropy oxide by multiple-heterojunction introduction

High-entropy oxides (HEOs), as multi-component ceramics with high configurational entropy, have been of recent interest due to their attractive properties including photocatalytic activity for H2 production and CO2 conversion. However, the photocatalytic activity of HEOs is still limited to ultraviolet light. In this study, to achieve visible-light-driven photocatalysis, 10 different heterojunctions were simultaneously introduced in the Ti-Zr-Nb-Ta-W-O system. The oxide, which was synthesized by a high-pressure torsion method and oxidation, successfully produced oxygen from water under visible light without co-catalyst addition. The photocatalytic performance was attributed to high visible-light absorption, low bandgap, appropriate band structure, presence of multiple heterojunctions and accordingly easy electron-hole separation and slow recombination. These results not only show the potential of high-entropy oxides as new visible-light-active photocatalysts, but also introduce the multiple-heterojunction introduction as a strategy to achieve photocatalysis under visible light.

Polytypic omega/omega-like transformation in a refractory high-entropy alloy

Understanding the atomistic details on microstructures and phase transformation mechanisms is essential to tailor the performances of materials. Refractory body-centered cubic (bcc) high-entropy alloys (HEAs) are considered as promising candidates for future applications in the high-temperature, superelasticity, and superconductivity fields. The classical omega (ω) transformation occurs in such systems is hardly expected due to the high configurational entropy and sluggish diffusion. Here, we confirmed unusual ω and ω-like transformations occurred in a configurational entropy stabilized refractory bcc TiZrNbTa model HEA facilitating the formation of colony hierarchical microstructures. These chemically ordered ω and polytyped ω-like superstructures nucleate from one of two phase-separated bcc products. Self-adapted atomic shuffling can convert the simple bcc lattice to the non-close-packed hexagonal ω superstructure, and a certain strain induced collective displacement of the (0001) atomic-layers along one of the <211¯0>ω directions can transition the traditional orthogonal ω to the non-orthogonal polytyped ω-like superstructures. Two ordered ω and/or ω-like superstructures with Ti, Zr, Nb, and Ta atoms occupied specific sites have thus been confirmed. Moreover, the chemistry, orientations, and interface relationships of the ω and polytyped ω-like superstructures were fully revealed by using aberration-corrected scanning transmission electron microscopy combined with first-principles calculations. These atomistic insights into the ω and polytyped ω-like superstructures transformations would provide theoretical guidance for the design of advanced refractory HEAs, especially for designing alloys with specific properties based on the control of transformed microstructures and interfacial modification.

Electrical Discharge Induced Bulk‐to‐Nanoparticle Transformation: Nano High‐Entropy Carbide as Catalysts for Hydrogen Evolution Reaction

AbstractHigh‐entropy carbide (HEC) is a promising alternative to precious metal catalysts for the hydrogen evolution reaction (HER). However, the preparation of nanoscale HECs is a great challenge although many methods have been developed to prepare bulk HEC materials. Herein, an electrical discharge induced bulk‐to‐nanoparticle transformation method is reported, by which well dispersed sub‐10 nm high entropy (MoWVNbTa)C nanoparticles with high‐density surface defects can be directly obtained by centrifugation of the waste liquid produced during wire‐cut electrical discharge machining of bulk HEC. The resultant HEC nanoparticles exhibit excellent catalytic activity and durability for HER, which is attributed to the combination of unique microstructure generated during the extremely nonequilibrium thermodynamic process and enhanced electronic effects induced by high configurational entropy. This facile and cost‐effective bulk‐to‐nanoparticle transformation method can be extended to other conductive materials and shed light on the development of high‐performance catalysts.

High-entropy alloys: properties and prospects of application as protective coatings

Alloys with high configurational entropy fundamentally differ from traditional alloys as they contain not one, but five or more basic elements with concentrations of 5 to 35 at.% each. Owing to the unique elemental composition, high-entropy alloys can have unusual functional properties such as high strength and wear resistance, exceptional heat resistance, good structural stability and good resistance to corrosion and oxidation. The review considers methods of synthesis of high-entropy alloys, methods and results of computer simulation of the high-entropy alloy structures and applications of such alloys as corrosion-, heat- and radiation-resistant materials and biomedical materials. Particular attention is paid to the prospects for the use of such alloys as protective coatings.The bibliography includes 352 references.

Tribological Performance of High-Entropy Coatings (HECs): A Review.

Surface coatings that operate effectively at elevated temperatures provide compatibility with critical service conditions as well as improved tribological performance of the components. High-entropy coatings (HECs), including metallic, ceramics, and composites, have gained attention all over the world and developed rapidly over the past 18 years, due to their excellent mechanical and tribological properties. High-entropy alloys (HEAs) are defined as alloys containing five or more principal elements in equal or close to equal atomic percentage. Owing to the high configurational entropy compared to conventional alloys, HEAs are usually composed of a simple solid solution phase, such as the BCC and FCC phases, instead of complex, brittle intermetallic phases. Several researchers have investigated the mechanical, oxidation, corrosion and wear properties of high-entropy oxides, carbides, borides, and silicates using various coating and testing techniques. More recently, the friction and wear characteristics of high-entropy coatings (HECs) have gained interest within various industrial sectors, mainly due to their favourable mechanical and tribological properties at high temperatures. In this review article, the authors identified the research studies and developments in high-entropy coatings (HECs) fabricated on various substrate materials using different synthesis methods. In addition, the current understanding of the HECs characteristics is critically reviewed, including the fabrication routes of targets/feedstock, synthesis methods utilized in various research studies, microstructural and tribological behaviour from room temperature to high temperatures.

High Configuration Entropy Activated Lattice Oxygen for O2 Formation on Perovskite Electrocatalyst

AbstractThe single‐phase oxides with elemental complexity and compositional diversity, usually named high entropy oxides, feature homogeneously dispersed multi‐metallic elements in equiatomic concentration. The unusual properties of high entropy oxides endow their potential application in clean‐energy‐related electrocatalysis. However, the possible fundamental relationship between configuration entropy and the underlying catalytic mechanism is still not well understood and established. Herein, a high entropy perovskite cobaltate consisting of five equimolar metals in the B‐site (Mg, Mn, Fe, Co, and Ni) is employed as an electrocatalyst for oxygen evolution reaction (OER). The configuration entropy serves as an effective tool to promote the intrinsic activity of the Co reactive site and manipulate the OER mechanism. The high entropy cobaltate demonstrates a lower overpotential of 320 mV at a current density of 10 mA cm−2, outperforming other counterparts. The X‐ray spectroscopies disclose the synergistic charge‐exchange effect among different cations and the formation of a new oxygen hole state. Combinatorially computational and experimental results unveil the enigma that the high configuration entropy leads to the random occupation of cations, facilitates the surface reconstruction, and benefits the formation of stable surface oxygen vacancies. Owing to these merits, the O2 formation is found to be kinetically favorable via the lattice oxygen mechanism.

Molten globule–like transition state of protein barnase measured with calorimetric force spectroscopy

SignificanceUnderstanding the molecular forces driving the unfolded polypeptide chain to self-assemble into a functional native structure remains an open question. However, identifying the states visited during protein folding (e.g., the transition state between the unfolded and native states) is tricky due to their transient nature. Here, we introduce calorimetric force spectroscopy in a temperature jump optical trap to determine the enthalpy, entropy, and heat capacity of the transition state of protein barnase. We find that the transition state has the properties of a dry molten globule, that is, high free energy and low configurational entropy, being structurally similar to the native state. This experimental single-molecule study characterizes the thermodynamic properties of the transition state in funneled energy landscapes.

Phase, mechanical property and corrosion resistance evaluation of W-Nb-Ta-Ti and W-Nb-Ta-Ti-N medium entropy alloy thin films

Multicomponent alloy thin films including high entropy alloy (HEA) and medium entropy alloy (MEA) thin films have drawn lots of attention from researchers and industries because of their outstanding properties, such as high hardness, good wear and corrosion resistance. Among several kinds of multicomponent alloy systems, the refractory HEA and MEA are characterized by their high temperature strength and stable thermal properties. In this work, the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films were fabricated by a magnetron co-sputtering system. The structure of W-Nb-Ta-Ti-N coatings changed from BCC to B1 FCC nitride phase when the nitrogen concentration reached 42.6 at.%. The microstructure of BCC structured W-Nb-Ta-Ti-N thin films changed from a coarse columnar to a dense feature as the nitrogen content increased from 0 to 16.2 at.%. A maximum hardness of 24.4 GPa was obtained for the BCC structured W34.3Nb21.7Ta26.4Ti1.4N16.2 thin film. The best adhesion property and the lowest coefficient of friction were found for the FCC W31.1Nb9.6Ta13.1Ti3.6N42.6 nitride thin film. The corrosion resistance of 304SS substrate in 5 wt% NaCl aqueous solution was greatly enhanced by the deposition of the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films. The best corrosion resistance can be seen for the nitrogen-free W37.9Nb25.8Ta28.8Ti7.5 thin film due to its dense microstructure, highest Ta and Nb contents, high configurational entropy and sluggish diffusion effects.

Crystal chemistry of rare-earth containing garnets: Prospects for high configurational entropy

Materials with high degrees of lattice configurational entropy are being studied to assess their potential as highly-stable materials with potentially new and unusual properties. This report involves an assessment of the prospects for producing novel, complex multi-component oxide compounds that have the garnet crystal structure. We examine the crystal chemistry of garnets in an effort to determine if it may be possible to design so-called “high-entropy oxide” garnets, i.e., garnets containing numerous cation components, such that the compounds are stable, monophasic, and offer the potential for new and unusual physical properties. In this report, we quantify configurational entropy for compounds such as garnet that possess numerous cation sublattices. Then, we consider coordination polyhedra and details of bonding in rare-earth containing garnets, in an effort to predict structural aspects of multi-component oxide garnets.

Improvement of critical current density of REBa2Cu3O7-δ by increase in configurational entropy of mixing.

REBa2Cu3O7-δ (RE123, RE: rare earth) is one of the high-temperature superconductors with a transition temperature (Tc) exceeding 90 K. Because of its high-Tc and large critical current density (Jc) under magnetic fields, RE123 superconductors have been expected to play a key role in superconductivity application. To accelerate application researches on RE123-based devices, further improvements of Jc characteristics have been desired. In this study, we investigated the effects of high-entropy alloying at the RE site on the superconducting properties, through the measurements of local (intra-grain) Jc () by a remanent magnetization method. We found that shows a trend to be improved when four or five RE elements are mixed at the RE site, which results in high configurational entropy of mixing (ΔSmix). All samples exhibited an order of few MA cm−2 which is a criterion for practical application and the highest resulted in a value of around 7.0 MA cm−2 at T = 2.0 K. Because high-entropy alloying can improve of RE123 superconductors, our entropy-engineering strategy introduced here would be useful for the development of RE123 superconducting materials available under high magnetic fields.

Determination of Location-Specific Solidification Cracking Susceptibility for a Mixed Dissimilar Alloy Processed by Wire-Arc Additive Manufacturing

Solidification cracking is a major obstacle when joining dissimilar alloys using additive manufacturing. In this work, location-specific solidification cracking susceptibility has been investigated using an integrated computational materials engineering (ICME) approach for a graded alloy formed by mixing P91 steel and Inconel 740H superalloy. An alloy mixture of 26 wt.% P91 and 74 wt.% Inconel 740H, with high configurational and total entropy, was fabricated using wire arc additive manufacturing. Microstructure characterization revealed intergranular solidification cracks in the FCC matrix, which increased in length along with the enrichment of Nb (~27 to 56 wt.%) and Cu (~87 wt.%) in the middle and top regions. DICTRA simulations to model location-specific solidification cracking susceptibility showed that the top region with the highest cooling rate (270 K/s) has the highest solidification cracking susceptibility in comparison with the middle and bottom regions. This is in good agreement with the experimentally observed varying crack length. From Scheil simulations, it was deduced that enrichment of Nb and Cu affected the solidification range as high as ~77%, in comparison with the matrix composition. The overall solidification cracking susceptibility and freezing range was highest for the 26 wt.% P91 alloy amongst the mixed compositions between P91 steel and 740H superalloy, proving that solidification characteristics play a major role in alloy design for additive manufacturing.

Porous high-entropy alloys as efficient electrocatalysts for water-splitting reactions

Porous high-entropy alloys (HEAs) have emerged as promising electrocatalysts for water-splitting reactions, owing to their rich dissimilar active sites, elemental diversity, and multiple functionalities. The rational design of HEAs for water-splitting attracted great interest in improving their current performance, so it is essential to provide timely updates on this field. This review emphasizes the preparation methods of porous HEAs and the effect of their salient features like high configurational entropy, cocktail effect, lattice distortion, and sluggish diffusion on oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). This mini-review also provides some insights into the current limitations and future perspectives to direct research on the development of ideal HEAs for OER and HER.