High-entropy Ceramics Research Articles

High Entropy Ceramics for Electromagnetic Functional Materials

AbstractMicrowave absorbing materials play an increasingly important role in modern electronic warfare technology for enhancing electromagnetic compatibility and suppressing electromagnetic interference. High‐entropy ceramics (HECs) possess extraordinary physical and chemical properties, and more importantly, the high tunability of multi‐component HECs has brought new opportunities to microwave absorbing materials. Rich crystallographic distortions and multi‐component occupancies enable HECs to have highly efficient microwave absorption properties, excellent mechanical properties, and thermal stability. Therefore, the structural advantages of HECs are integrated from comprehensive perspectives, emphasizing on the role of dielectric and magnetic properties in the absorption phenomenon. Strategies are proposed to improve the microwave absorption capacity of HECs, including composition optimization, microstructure engineering, and post‐treatment technology. Finally, the problems and obstacles associated with high‐entropy materials (HEMs) research are discussed. The innovative design concepts of high‐entropy microwave absorbing ceramics are highlighted.

High-entropy ceramics

High-entropy ceramics

Investigation of Thermal Properties of Rare-Earth X2-Type Monosilicates through High-Entropy Design and Defect Engineering

Rare earth X2-type monosilicates with low thermal conductivity are crucial for material performance in extreme environments. Three high-entropy ceramics, (Er1/4Tm1/4Yb1/4Lu1/4)2SiO5, (Y1/4Er1/4Tm1/4Yb1/4)2SiO5, and (Gd1/4Dy1/4Er1/4Yb1/4)2SiO5, were synthesized in this study. Among these, the thermal conductivity of (Y1/4Er1/4Tm1/4Yb1/4)2SiO5 at 1200 °C is 1.03 W m–1 K–1. Concurrently, the stable existence of dislocation arrays was observed in the quaternary high-entropy monosilicate system of (Y1/4Er1/4Tm1/4Yb1/4)2SiO5. The scattering of medium-frequency phonons can be enhanced by the presence of dislocations, leading to a reduction in thermal conductivity. This provides direct experimental evidence supporting the feasibility of reducing material thermal conductivity through high-entropy design by introducing dislocations.

Enhanced low-field energy storage performance and dielectric stability in (Bi0.4Sr0.2K0.2Na0.2)(Ti1-xZrx)O3 high-entropy ceramics via B-site modification

The current global energy situation is tense, necessitating the development of high-efficiency, low-cost, and eco-friendly energy materials. In this study, a series of perovskite lead-free relaxor ferroelectric ceramics, denoted as (Bi0.4Sr0.2K0.2Na0.2)(Ti1-xZrx)O3 (BSKNT-xZr) were designed to enhance the storage performance. The findings indicate that all samples exhibit a single perovskite structure. As the Zr4+ content increases, the configurational entropy of the samples increases, the cell volume expands, and the hysteresis loops become finer, while maintaining a high maximum polarization (Pm) and effectively enhancing the energy storage performance. For the ceramic with x = 0.10, the energy density (Wtot), recoverable energy density (Wrec), and energy storage efficiency (η) values were determined to be 3.16 J/cm3, 2.67 J/cm3, and 84.3%, respectively, under an electric field of 230 kV/cm. Moreover, the introduction of Zr4+ reduces the relative permittivity and broadens the temperature range (ΔT) that simultaneously satisfies Δε/ε150°C ≤ ±15% and 0 ≤ tanδ ≤ 0.02. This investigation underscores the potential of BSKNT-xZr ceramics as high-performance, cost-effective, and environmentally friendly energy materials for addressing global energy requirements.

High entropy alloys: Next-generation material for space exploration

High entropy materials (HEMs) have become a prominent research focus because of their remarkable properties, such as superior thermal stability, mechanical strength, and oxidation resistance, including High entropy alloys (HEAs), high-entropy polymers (HEPs), and high-entropy ceramics (HECs). These unique materials hold significant potential for advanced applications across leading industries, including aerospace, defense, military, biomedical, and chemical sectors. An overview of a diverse range of HEAs, their effects, classification, and various entropy alloy manufacturing techniques is presented to discover the optimized HEAs for significant applications particularly relevant to the aerospace industry. Their exceptional performance in the numerous fields of applications has made HEAs a promising alternative over solitary metals, alloys, and composites. Furthermore, it highlights numerous challenges faced in manufacturing. It presents a detailed analysis of the future scope of their development to enhance their applicability in aerospace and other high-demand fields.

Coupling Residual Stress Field to Enhance the Simulation Accuracy of Crack Propagation and Mechanical Responses of High Entropy Ceramics Reinforced by Graphene and Alumina

Coupling Residual Stress Field to Enhance the Simulation Accuracy of Crack Propagation and Mechanical Responses of High Entropy Ceramics Reinforced by Graphene and Alumina

Effect of Sintering Process on Microstructure and Properties of (Zr0.2Ta0.2Ti0.2Cr0.2Hf0.2)Si2 High-Entropy Silicide Ceramics

In this study, five kinds of (Zr0.2Ta0.2Ti0.2Cr0.2Hf0.2)Si2 high-entropy ceramics were prepared by a two-step method under different vacuum pressureless pre-sintering processes, and the microstructures and mechanical properties of the ceramics under different parameters of the pre-sintering process were systematically discussed. The results show that the physical structure of the ceramic samples remains basically unchanged by changing the pre-sintering conditions; the longer the holding time of the initial pre-sintering, the higher the densification of the samples and all of them are above 95%. The hardness of the ceramics was around 10 GPa, with the best hardness of 10.11 GPa at 1300 °C for 3 h. This conclusion provides data support for the optimization of the high-entropy ceramics preparation process.

Studies on synthesis, Raman, and electrical properties of novel spinel high entropy ceramics

Studies on synthesis, Raman, and electrical properties of novel spinel high entropy ceramics

Novel high-entropy (La0.35Gd0.35Y0.35Sm0.35Yb0.6)Zr2O7 thermal barrier coatings: Thermal cycling performance and failure behavior

The high-entropy ceramic (HEC) (La0.35Gd0.35Y0.35Sm0.35Yb0.6)Zr2O7 has emerged as a strong candidate for thermal barrier coatings (TBCs) due to its exceptional thermal properties. We investigated the thermal shock resistance of HEC–lanthanum zirconate (LZ)/yttria partially stabilized zirconia (YSZ) (i.e., the HEC coating) and LZ/YSZ (i.e., the LZ coating) double-ceramic-layer TBCs fabricated via plasma spraying. During thermal shock testing at 1100°C, the LZ coating failed after 60 ± 3 cycles, while the HEC coating had a considerably longer thermal cycling lifetime of 135 ± 5 cycles. The HEC coating’s superior performance is attributable to its enhanced oxygen barrier properties and inherent lattice disorder; the former reduced the growth rate of the thermally grown oxide, and the latter increased lattice defects and distortion. These factors helped improve the thermal expansion coefficient and reduced interlayer thermal stress accumulation. Furthermore, the higher fracture toughness of the HEC layer impeded crack propagation, collectively enhancing the TBCs’ thermomechanical shock resistance. These findings underscore the potential of (La0.35Gd0.35Y0.35Sm0.35Yb0.6)Zr2O7 as a robust material for extending the service life of TBCs in high-temperature environments.

The influence of the elemental valence on the thermophysical properties of high entropy (La0.2Sm0.2Eu0.2Yb0.2Y0.2)2(Ce0.5Zr0.5)2O7 coatings for thermal barrier application

Commercial yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) are no longer sufficient for the stringent demands in the high operating temperature and excellent thermophysical properties of the high-performance gas turbines and aviation engines. High entropy ceramics, distinguished by their superior thermophysical properties, have risen as a potential substitute for TBCs. However, the realm of atmospheric plasma spraying (APS) in the creation of these advanced TBCs remains relatively unexplored. In this work, three distinct high-entropy (La0.2Sm0.2Eu0.2Yb0.2Y0.2)2(Ce0.5Zr0.5)2O7 coatings were developed through the meticulous alteration of spraying power. The effects of spraying power on the microstructure, valence states of constituent elements and thermophysical properties of the coatings were deeply investigated. The results indicated that all the as-sprayed coatings exhibit a defect fluorite structure. Spraying power does have a significant impact on the thermophysical properties of the coatings. With the decrease in spraying power, the thermal conductivity of the coatings shows a progressive reduction, whereas the coefficient of thermal expansion (CTE) exhibits a gradual increase. This trend is closely related to valence states of constituent elements in the coatings. The resulting coating exhibits a low thermal conductivity of 0.54 W⋅m-1⋅K-1, a high CTE of 11.22×10-6·K-1 and a superior phase stability at elevated temperatures.

Effect of Cr, Al and Mo additives on the wetting characteristics of molten Ni on (Ti, Zr, Hf, Nb, Ta)C high entropy ceramics

For the first time, the wetting behavior of the (Ti, Zr, Hf, Nb, Ta)C) high entropy carbide ceramics by molten Ni-based alloys was investigated using a sessile drop technique in a vacuum environment. Adding 10wt% of Cr, Mo, or Al into Ni resulted in final contact angles of 14°, 10°, and 14° on the (Ti, Zr, Hf, Nb, Ta)C substrate, respectively. The interaction mechanism between (Ti, Zr, Hf, Nb, Ta)C and Ni-based alloys occurs in two stages: the dissolution and interaction of the elements Ti, Zr, Hf with the alloys and the dissolution of NbC and TaC at the grain boundaries. SEM observations revealed that Cr and Al additives do not interact with carbides, while Mo was dissolved in carbides. Due to the low contact angle, minimal interaction region between alloy and ceramic, and short time of drop spreading, NiAl alloy is proven to be a promising binder for the HEC-based composites.

Effect of processing parameters and carbon to metal ratio on microstructure and mechanical properties of (MoTaTiVW)Cx high entropy carbide produced by reactive spark plasma sintering

(MoTaTiVW)Cx high entropy ceramics with varying carbon to metal ratio in the range of 0.75-0.97 were synthesized by by reactive spark plasma sintering. The effect of ball milling time on particle size, phase evolution and carbon pick-up due to toluene decomposition were studied. Formation of single-phase high entropy carbide having face-centered cubic (FCC) crystal structure was confirmed by X-ray diffraction (XRD), electron backscattered diffraction (EBSD) and Selected area diffraction pattern (SAED) analysis of the sintered compacts. Transmission Kikuchi Diffraction images revealed presence of equiaxed nature of the grains. Transmission electron microscopy images revealed the presence of an intergranular phase at grain boundaries and triple junctions. 3D-Atom Probe Tomography studies showed uniform distribution of elements within the grains with some segregation of impurity elements Fe and Co to the grain boundaries indicating minor contribution of liquid phase sintering to densification. The grain size of single-phase sintered compacts ranged between 1.69 ± 0.60 μm to 4.6 ± 1.0 μm. A low sintering temperature and higher milling time resulted in finer grain size The microhardness was found to increase with milling time and C/M ratio. The microhardness, Young’s modulus and indentation fracture toughness lied between 2221 HV0.1 to 2732 HV0.1, 370 GPa to 473 GPa, 3.6 MPa.m1/2 to 4.4 MPa.m1/2, respectively. The highest microhardness and indentation fracture toughness was found to be 2732 ± 80 HV0.1 and 4.4 MPa.m1/2 on par with reported literature for other high entropy carbides.

Design and synthesis of high-entropy A2B2O7-type pyrochlore ceramics for the immobilization of molten salt radwastes

Pyrochlore-based high-entropy ceramics can encapsulate multiple elements with different valences, making them promising for immobilizing high-level radioactive nuclides in molten salt radwaste. This approach addresses key challenges in dry reprocessing and molten salt reactor waste management. In this study, a single-phase pyrochlore-based high-entropy ceramic is synthesized to incorporate NdF3 and CeF3 as simulated molten salt radwastes. Various synthesis components have been explored, and the ceramics were characterized using x-ray diffraction (XRD) and Raman spectroscopy. Comparative analysis revealed that the size disorder is the critical factor to synthesize single-phase pyrochlore-based high-entropy ceramics. The effects of elemental ratio and the presence of variable valence elements on the synthesis of single-phase pyrochlore-based high-entropy ceramics are elucidated through the concept of size disorder. Two single-phase pyrochlore compositions have been successfully synthesized: #HE4 (Nd2(Ti0.25Zr0.25Hf0.25Sn0.25)2O7) and #HECe0.1 (Nd2(Zr0.3Hf0.2Sn0.2Nb0.2Ce0.1)2O7). These samples were tested with a 7-day leaching experiment using the Product Consistency Test Method PCT-B. The normalized release rates of all elements in #HE4 ranged from 10-7 to 10-9 g·m-2·d-1, indicating excellent chemical durability. These findings suggest that medium- and high-entropy pyrochlore-based ceramics are effective for immobilizing radioactive nuclides in molten salt radwastes.

Recent Advances in High-Entropy Ceramics: Synthesis Methods, Properties, and Emerging Applications

High-entropy ceramics (HECs) represent an emerging class of materials composed of at least five different cations or anions in near-equiatomic proportions, garnering significant attention due to their extraordinary functional and structural properties. While multi-component ceramics have played a crucial role for many years, the concept of high-entropy materials was first introduced eighteen years ago with the synthesis of high-entropy alloys, and the first high-entropy nitride films were reported in 2014. These newly developed materials exhibit superior properties over traditional ceramics, such as enhanced thermal stability, hardness, and chemical resistance, making them suitable for a wide range of applications. High-entropy carbides, borides, oxides, oxi-carbides, oxi-borides, and other systems fall within the HEC category, typically occupying unique positions within phase diagrams that lead to novel properties. HECs are particularly well suited for high-temperature coatings, for tribological applications where low thermal conductivity and similar heat coefficients are critical, as well as for energy storage and dielectric uses. Computational tools like CALPHAD streamline the element selection process for designing HECs, while innovative, energy-efficient synthesis methods are being explored for producing dense specimens. This paper provides an in-depth analysis of the current state of the compositional design, the fabrication techniques, and the diverse applications of HECs, emphasizing their transformative potential in various industrial domains.

High-entropy processed high quality and low-temperature cofired LiMgPO4-based dielectric ceramics for low-loss packaged millimeter-wave filters

In this work, we successfully integrated the high-entropy concept into LiMgPO4-based ceramics by strategically substituting Mg2+ with various divalent ions. Through a low-temperature solid-phase reaction method, a series of high-entropy LiMg0.9R0.1PO4 (R = Ni, NiCo, NiCoZn, NiCoZnCu, NiCoZnCuMn) ceramics were prepared successfully, and their MW dielectric properties were found to be heavily influenced by the ionic character, lattice energy, bond energy, entropy, ion radius disorder, and electronegativity of chemical bonds. Remarkably, LiMg0.9(Ni0.2Co0.2Zn0.2Cu0.2Mn0.2)0.1PO4 (LM5RP) ceramics exhibited exceptional MW dielectric properties (εr = 7.43, τf = − 27.6 ppm/°C, and Q × f = 83,216 GHz@13 GHz and 105,889 GHz@28 GHz) when sintered at an extraordinarily low temperature of 900 °C for 2 h. To demonstrate the real-world applicability of the LM5RP high-entropy ceramic, we designed and fabricated a state-of-the-art millimeter-wave (mmWave) filter, operating at 28 GHz, using low-temperature co-fired ceramic (LTCC) packaging technology. The filter exhibited unparalleled performance, featuring a low insertion loss (0.9 dB) and wide stopband suppression (> 17 dB @ 2.14 f0). These groundbreaking findings underscore the immense potential of high-entropy ceramics in revolutionizing advanced MW applications, particularly in the domain of B5G/6 G mmWave communication systems.

Giant Capacitive Energy Storage in High-Entropy Lead-Free Ceramics with Temperature Self-Check.

Considering the large demand for electricity in the era of artificial intelligence and big data, there is an urgent need to explore novel energy storage media with higher energy density and intelligent temperature self-check functions. High-entropy (HE) ceramic capacitors are of great significance because of their excellent energy storage efficiency and high power density (PD). However, the contradiction between configurational entropy and polarization in traditional HE systems greatly restrains the increase in energy storage density. Herein, the contradiction is effectively solved by regulating the octahedral tilt and cationic displacement in ABO3-type perovskite HE ceramics, i.e., (1-x)[0.6(Bi0.47Na0.47Yb0.03Tm0.01)TiO3-0.4(Ba0.5Sr0.5)TiO3]-xSr(Zr0.5Hf0.5)O3 (BNYTT-BST-xSZH). Combining the tape-casting process and cold isostatic pressing, the optimal BNYTT-BST-0.06SZH ceramic displays a large recoverable energy storage density (10.46 J cm-3) at 685kV cm-1 and a high PD (332.88 MW cm-3). More importantly, due to Tm/Yb codoping, abnormal fluorescent negative thermal expansion and excellent real-time temperature sensing are developed, thus the application of fault detection and warning in high-voltage transmission line systems is conceptualized. This study provides an effective strategy for enhancing the polarization of energy-storing HE ceramics and offers a promising material for overcoming the problems of insufficient capacitor density and thermal runaway in terminal communication.

Full-scale insight into high-entropy ceramics from basic concepts, synthesis technologies, structural characteristics, and properties to application prospects

High-entropy ceramics (HECs) are an emerging material system that has gained significant attention and become a focal point of research due to their unique structure and outstanding performance. This paper provides a comprehensive examination of the basic concepts, synthesis methods, structural characteristics, unique properties, and application prospects of HECs. It begins with an overview of the basic concepts and historical context, followed by a detailed comparison of synthesis techniques, including both traditional and innovative approaches. The paper then analyzes the structural characteristics and phase compositions of HECs, particularly focusing on oxide, carbide, boride, and other non-oxide ceramics. In addition, it delves into the mechanical, thermal, electrical, and magnetic properties of HECs. The article also reviews the applications of HECs in high-temperature structural materials, functional materials, high-performance coatings, and biomedical implants. Finally, it discusses the future challenges and development pathways for HECs. By highlighting new applications and transformative possibilities, this study not only sheds light on cutting-edge research but also emphasizes the significant impact of HECs on sustainable material development. The integration of machine learning and artificial intelligence can further unlock the unique structural capabilities of HECs, offering substantial potential for advancements in emerging fields like new energy and biomedicine.

The effect of entropy on the structure and aqueous leaching resistance of nano monazite-type phosphates

Monazite, with its unique chemical composition and stable crystal structure, shows significant potential for immobilizing high-level radioactive waste. In this study, a series of monazite ceramics were synthesized to study the effect of entropy change on their structure and aqueous durability. The synthesized ceramics exhibit a monoclinic structure (P21/n), with an average grain size below 80 nm. MCC-1 leaching tests reveal that the normalized leaching rate decreases over time but increases with higher entropy. The five-element high-entropy ceramics have an average leaching rate of 4.2 × 10⁻³ g·m⁻2 d⁻1. Notably, the higher leaching rate in high-entropy nanocrystalline monazites is likely attributed to the reduced grain size. The presence of numerous grain boundaries tends to mitigate the precipitation inhibition effect typically associated with high-entropy ceramics. These findings offer insights into the role of entropy and grain size in ceramic materials for radioactive waste immobilization.

Optimization of Energy Storage Performance in NaNbO3-Based High Entropy Ceramics via MnO Doping

Excellent comprehensive energy storage performance is essential to ensure a favorable application prospect for high entropy dielectric capacitors. In this work, the energy storage performance of 0.8(Na0.5Li0.5NbO3)-0.2(Sr0.5Bi0.5)(Fe0.5Ti0.25Zr0.25)O3 ceramics with high entropy was improved by incorporating various contents of MnO. The results show that with the addition of MnO, the relaxation behavior is enhanced, significantly improving energy storage performance, and a recoverable energy density of 7.93 J/cm³ and energy efficiency of 90.6% is achieved for [0.8(Na0.5Li0.5NbO3)-0.2(Sr0.5Bi0.5)(Fe0.5Ti0.25Zr0.25)O3]-0.05MnO under a 510 kV/cm electric field. Compared with non-MnO-doped ceramics, the size of the polar nanoregions (PNRs) is significantly reduced. It also shows remarkable stability to temperature and frequency. This study validates that integrating MnO effectively enhances the energy storage performance of high-entropy ceramics.

Dual-phase zirconate/tantalate high-entropy ceramics boost thermal properties and fracture toughness for thermal barrier coating materials

Working temperatures, thermal insulation performance, and life span of thermal barrier coatings (TBCs) are primarily influenced by their high-temperature stability, thermal expansion coefficients (TECs), thermal conductivity, and fracture toughness. To address the limitations of current zirconate- and tantalate-based oxides, dual-phase zirconate/tantalate high-entropy ceramics (HECs) are designed and synthesized to improve their thermal and mechanical properties. The combined effects of high entropy, high concentrations of oxygen vacancies, and relatively low phonon velocity result in glass-like thermal conductivity, with a minimum value of 1.55 W m−1 K−1 at 1200 °C. The high TECs (10.6–10.9 × 10−6 K−1 at 1400 °C) and exceptional high-temperature stability demonstrate that these materials can withstand 1300 °C for more than 300 h, significantly surpassing the performance of traditional yttria-stabilized zirconia (YSZ). Compared with YSZ (3.6 MPa m1/2) and YTaO4 (2.5 MPa m1/2), the increments in fracture toughness (4.4 MPa m1/2) of dual-phase zirconate/tantalate HECs are as high as 22.2% and 76.0%, respectively. It is evident that the designed dual-phase zirconate/tantalate HECs can effectively promote thermal properties and fracture toughness, positioning them as the next-generation TBCs with high operating temperatures and outstanding thermal insulation performance.