High-entropy ferroelastic rare-earth tantalite ceramic: (Y0.2Ce0.2Sm0.2Gd0.2Dy0.2)TaO4

In this study, high-entropy rare-earth tantalate ceramics (Y_0.2Ce_0.2Sm_0.2Gd_0.2Dy_0.2)TaO₄ ((5RE_0.2)TaO₄) have been successfully fabricated. The possibility of formation of (5RE_0.2)TaO₄ was verified via first-principles calculations. In addition, the phase structure, ferroelastic toughening mechanism, thermophysical, and mechanical properties were systematically investigated. The (5RE_0.2)TaO₄ ceramics have lower phonon thermal conductivity (1.2–2.6 W·m^–1·K^–1) in the entire temperature range than that of RETaO₄ and YSZ. (5RE_0.2)TaO₄ has a higher fracture toughness and lower brittleness index than YSZ. The thermal expansion coefficients of (5RE_0.2)TaO₄ are as high as 10.3 × 10^-6 K^–1 at 1200°C and Young's modulus is 66–189 GPa, and thus, (5RE_0.2)TaO₄ possesses great potential for application in thermal barrier coatings (TBCs).     

High-entropy rare-earth disilicate (Lu0.2Yb0.2Er0.2Tm0.2Sc0.2)2Si2O7: A potential environmental barrier coating material

A new high-entropy ceramic (Lu_0.2Yb_0.2Er_0.2Tm_0.2Sc_0.2)₂Si₂O₇ ((5RE_0.2)₂Si₂O₇) was proposed as a potential environmental barrier coating (EBC) material for ceramics matrix composites in this work. Experimental results showed that the (5RE_0.2)₂Si₂O₇ synthesized by solid-phase sintering was a monoclinic solid solution and had good phase stability proved by no obvious absorption/exothermic peak in the DSC curve from room temperature to 1400 °C. It performed a lower coefficient of thermal expansion (2.08 ×10^?6-4.03 ×10^?6 °C^?1) and thermal conductivity (1.76–2.99 W?m^?1?°C^?1) compared with the five single principal RE₂Si₂O₇. In water vapor corrosion tests, (5RE_0.2)₂Si₂O₇ also exhibited better water vapor corrosion resistance attributed to the multiple doping effects. The weight loss was only 3.1831 × 10^?5 g?cm^?2 after 200 h corrosion at 1500 °C, which was lower than that of each single principal RE₂Si₂O₇. Therefore, (5RE_0.2)₂Si₂O₇ could be regarded as a remarkable candidate for EBCs.     

Ultrafast high-temperature sintering of (Y0.2Dy0.2Er0.2Tm0.2Yb0.2)4Hf3O12 high-entropy ceramics with defective fluorite structure

An entropy-stabilized rare earth hafnate (Y_0.2Dy_0.2Er_0.2Tm_0.2Yb_0.2)₄Hf₃O₁₂ (5RH) with defective fluorite structure was successfully prepared by the emerging ultrafast high-temperature sintering (UHS) in less than six minutes. The 5RH ceramic possessed a higher thermal expansion coefficient (11.23 ×10^?6/K, 1500 °C) and extremely low thermal conductivity (0.94 W/(m·k), 1300 ℃) owing to the larger lattice distortion of high-entropy materials. After high-temperature annealing at 1500 ℃, the 5RH showed extremely sluggish grain growth characteristics and excellent high-temperature phase stability, mainly attributed to the non-equilibrium sintering characteristic of the UHS and the sluggish diffusion effect of high-entropy materials. Therefore, (Y_0.2Dy_0.2Er_0.2Tm_0.2Yb_0.2)₄Hf₃O₁₂ has excellent potential as a next-generation thermal barrier coating material to replace traditional Y₂O₃ stabilized ZrO₂. Finally, using the UHS to prepare high-entropy ceramics provides a new technique for fast-sintering and developing next-generation thermal barrier coating materials.     

Multi-component strategy for remarkable suppression of thermal conductivity in strontium diyttrium oxide: The case of high-entropy Sr(Y0.2Sm0.2Gd0.2Dy0.2Yb0.2)2O4 ceramic

Anti-spinel oxide SrY₂O₄ has attracted extensive attention as a promising host lattice due to its outstanding high-temperature structural stability and large thermal expansion coefficient (TEC). However, the overhigh thermal conductivity limits its application in the field of thermal barrier coatings. To address this issue, a novel high-entropy Sr(Y_0.2Sm_0.2Gd_0.2Dy_0.2Yb_0.2)₂O₄ ceramic was designed and synthesized for the first time via the solid-state method. It is found that the thermal conductivity of Sr(Y_0.2Sm_0.2Gd_0.2Dy_0.2Yb_0.2)₂O₄ is reduced to 1.61 W·m⁻¹·K⁻¹, 53 % lower than that of SrY₂O₄ (3.44 W·m⁻¹·K⁻¹) at 1500 °C. Furthermore, reasonable TEC (11.53 ×10⁻⁶ K⁻¹, 25 °C ∼ 1500 °C), excellent phase stability, and improved fracture toughness (1.92 ± 0.04 MPa·m^1/2) remained for the high-entropy Sr(Y_0.2Sm_0.2Gd_0.2Dy_0.2Yb_0.2)₂O₄ ceramic, making it a promising material for next-generation thermal barrier coatings.     

Rare-earth-tantalate high-entropy ceramics with sluggish grain growth and low thermal conductivity

A series of rare-earth-tantalate high-entropy ceramics ((5RE_0.2)Ta₃O₉, where RE = five elements chosen from La, Ce, Nd, Sm, Eu and Gd) were prepared by conventional sintering in air at 1500 ^°C for 10 h. The (5RE_0.2)Ta₃O₉ high-entropy ceramics exhibit an orthogonal structure and sluggish grain growth. No phase transition occurs in the test temperature of 25–1200 ^°C. The thermal conductivities of all (5RE_0.2)Ta₃O₉ ceramics are in the range of 1.14–1.98 W m^?1 K^?1 at a test temperature of 25–500 ^°C, approximately half of that of YSZ. The sample of (Gd_0.2Ce_0.2Nd_0.2Sm_0.2Eu_0.2)Ta₃O₉ exhibits a low glass-like thermal conductivity with a value of 1.14 W m^?1 K^?1 at 25 ^°C. The thermal expansion coefficient of (5RE_0.2)Ta₃O₉ ceramics ranges from 5.6 × 10^?6 to 7.8 × 10^?6 K^?1 at 25–800 ^°C, and their fracture toughness is high (3.09–6.78 MPa·m^1/2). The results above show that (5RE_0.2)Ta₃O₉ ceramics could be a promising candidate for thermal barrier coatings.     

High-entropy La(Fe0.2Co0.2Ni0.2Cr0.2Mn0.2)O3 ceramic exhibiting high emissivity and low thermal conductivity

A novel, high-entropy, perovskite-structured, solid solution La(Fe_0.2Co_0.2Ni_0.2Cr_0.2Mn_0.2)O₃ ceramic was successfully synthesized via high-temperature solid-state reaction. The crystal structure, microstructure, infrared emissivity, and thermophysical properties were investigated. The experimental results indicated that La(Fe_0.2Co_0.2Ni_0.2Cr_0.2Mn_0.2)O₃ exhibited an infrared emissivity as high as .92 in the near-infrared region of .76–2.50 μm. The thermal conductivity was 1.38–1.72 W m⁻¹ K⁻¹ in the temperature range of 25–1200°C.     

Phase evolution and thermal stability of novel high-entropy (Mo0.2Nb0.2Ta0.2V0.2W0.2)Si2 ceramics

Owing to the high melting points and high-temperature stability, transition-metal disilicides are potential components for aerospace, automotive, and industrial engineering applications. However, unwanted oxidation known as PEST oxidation severely limits their application owing to the formation of volatile transition metal oxides, especially in the temperature range of 500–1000 °C. To overcome this problem, a new class of high-entropy disilicides, (Mo_0.2Nb_0.2Ta_0.2V_0.2W_0.2)Si₂, was selected by first-principles calculations and then successfully fabricated using a hot-pressing sintering technique. Furthermore, the phase evolution, thermal expansion behavior, thermal conductivity, and oxidation behavior were systematically investigated. Compared with MoSi₂, (Mo_0.2Nb_0.2Ta_0.2V_0.2W_0.2)Si₂ possessed a lower thermal conductivity (10.9–14.7 W·m^?1·K^?1) at 25–1000 °C, higher thermal expansion coefficients (8.6 ± 1.3^–6 K^–1) at 50–1200 °C, and especially an excellent thermal stability at 500–1000 °C owing to slow diffusion and selective oxidation. This work provides a strong foundation for the synthesis and application of high-entropy disilicides.     

Marked reduction in the thermal conductivity of (La0.2Gd0.2Y0.2Yb0.2Er0.2)2Zr2O7 high-entropy ceramics by substituting Zr4+ with Ti4+

The (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂(Zr_1-xTi_x)₂O₇ (x = 0–0.5) high-entropy ceramics were successfully prepared by a solid state reaction method and their structures and thermo-physical properties were investigated. It was found that the high-entropy ceramics demonstrate pure pyrochlore phase with the composition of x = 0.1–0.5, while (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂Zr₂O₇ shows the defective fluorite structure. The sintered high-entropy ceramics are dense and the grain boundaries are clean. The grain size of high-entropy ceramics increases with the Ti⁴⁺ content. The average thermal expansion coefficients of the (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂(Zr_1-xTi_x)₂O₇ high-entropy ceramics range from 10.65 × 10^?6 K^?1 to 10.84 × 10^?6 K^?1. Importantly, the substitution of Zr⁴⁺ with Ti⁴⁺ resulted in a remarkable decrease in thermal conductivity of (La_0.2Gd_0.2Y_0.2Yb_0.2Er_0.2)₂(Zr_1-xTi_x)₂O₇ high-entropy ceramics. It reduced from 1.66 W m^?1 K^?1 to 1.20 W m^?1 K^?1, which should be ascribed to the synergistic effects of mass disorder, size disorder, mixed configuration entropy value and rattlers.     

Potential thermal barrier coating materials: RE3NbO7 (RE=La, Nd,Sm, Eu,Gd, Dy) ceramics

In this work, RE₃NbO₇ ceramics are synthesized via solid‐state reaction and the phase structure is characterized by X‐ray diffraction and Raman spectroscopy. The relationship between crystal structure and thermophysical properties is determined. Except Sm₃NbO₇, each RE₃NbO₇ exhibits excellent high‐temperature phase stability. The thermal expansion coefficients increase with the decreasing RE³⁺ ionic radius, which depends on the decreasing crystal lattice energy and the maximum value reaches 11.0 × 10^?6 K^?1 at 1200°C. The minimum thermal conductivity of RE₃NbO₇ reaches 1.0 W m^?1 K^?1 and the glass‐like thermal conductivity of Dy₃NbO₇ is dominant by the high concentration of oxygen vacancy and the local structural order. The outstanding thermophysical properties pronounce that RE₃NbO₇ ceramics are potential thermal barrier coating materials.     

New class of high-entropy defect fluorite oxides RE2(Ce0.2Zr0.2Hf0.2Sn0.2Ti0.2)2O7 (RE = Y,Ho, Er,or Yb) as promising thermal barrier coatings

High-entropy ceramics exhibit great application potential as thermal barrier coating (TBC) materials. Herein, a series of novel high-entropy ceramics with RE₂(Ce_0.2Zr_0.2Hf_0.2Sn_0.2Ti_0.2)₂O₇ (RE₂HE₂O₇, RE = Y, Ho, Er, or Yb) compositions were fabricated via a solid-state reaction. X-ray diffraction (XRD) and energy dispersive spectrometry (EDS) mapping analyses confirmed that RE₂HE₂O₇ formed a single defect fluorite structure with uniform elemental distribution. The thermophysical properties of the RE₂HE₂O₇ ceramics were investigated systematically. The results show that RE₂HE₂O₇ ceramics have excellent high-temperature phase stability, high thermal expansion coefficients (10.3–11.7 × 10^?6 K^-1, 1200 ℃), and low thermal conductivities (1.10-1.37 W m^-1 K^-1, 25 ℃). In addition, RE₂HE₂O₇ ceramics have a high Vickers hardness (13.7–15.0 GPa) and relatively low fracture toughness (1.14-1.27 MPa m^0.5). The outstanding properties of the RE₂HE₂O₇ ceramics indicate that they could be candidates for the next generation of TBC materials.     

Thermal properties of (Zr0.2Ce0.2Hf0.2Y0.2RE0.2)O1.8 (RE= La,Nd and Sm) high entropy ceramics for thermal barrier materials

The high-entropy ceramic materials (Zr_0.25Ce_0.25Hf_0.25Y_0.25)O_1.875 (H-0) and (Zr_0.2Ce_0.2Hf_0.2Y_0.2RE_0.2)O_1.8 (H-RE) (RE = La, Nd and Sm) with fluorite structure and homogeneous element distribution were prepared. With fluorite structure, fine grain size and high density, the H-0 and H-RE ceramics displayed low thermal conductivity, suitable thermal expansion coefficient, high hardness and fracture toughness. The effect of La, Nd and Sm on the mechanical, heat conductivity and heat expansion properties of high entropy ceramics were discussed. The single-phase high-entropy ceramic materials in this work are very suitable for application as thermal barrier materials.     

High-entropy rare earth titanates with low thermal conductivity designed by lattice distortion

High-entropy single-phase rare earth titanates (RE_0.2Gd_0.2Ho_0.2Er_0.2Yb_0.2)₂Ti₂O₇ (RE = Sm, Y, Lu) were designed and synthesized successfully, in which their lattice distortion was quantitatively described by mass disorder and size disorder. It is worth mentioning that (Y_0.2Gd_0.2Ho_0.2Er_0.2Yb_0.2)₂Ti₂O₇ could obtain the low thermal conductivity (1.51 W·m⁻¹·K⁻¹, 1500°C), high thermal expansion coefficient (average, 11.69×10⁻⁶ K⁻¹, RT ∼1500°C) and excellent high-temperature stability. In addition, the relationship between the microstructure and thermal transport behaviors has been studied at the atomic scale. Due to the disorder of A-site ions, severe lattice distortion occurred in specific crystal planes, and the large mass difference between Y³⁺ and other RE³⁺ further causes mass fluctuation and results in lower thermal conductivity. Compared with YSZ, the high-entropy rare earth titanate (Y_0.2Gd_0.2Ho_0.2Er_0.2Yb_0.2)₂Ti₂O₇ has lower thermal conductivity, higher thermal expansion coefficient, and excellent high-temperature stability, which has great potential for application in the thermal protection field.     

High-entropy (Ho0.2Y0.2Dy0.2Gd0.2Eu0.2)2Ti2O7/TiO2 composites with excellent mechanical and thermal properties

High-performance ceramics with low thermal conductivity, high mechanical properties, and idea thermal expansion coefficients have important applications in fields such as turbine blades and automotive engines. Currently, the thermal conductivity of ceramics has been significantly reduced by local doping/substitution or further high-entropy reconfiguration of the composition, but the mechanical properties, especially the fracture toughness, are insufficient and still need to be improved. In this work, based on the high-entropy titanate pyrochlore, TiO₂ was introduced for composite toughening and the high-entropy (Ho_0.2Y_0.2Dy_0.2Gd_0.2Eu_0.2)₂Ti₂O₇-xTiO₂ (x = 0, 0.2, 0.4, 1.0 and 2.0) composites with high hardness (16.17 GPa), Young's modulus (289.3 GPa) and fracture toughness (3.612 MPa·m^0.5), low thermal conductivity (1.22 W·m⁻¹·K⁻¹), and thermal expansion coefficients close to the substrate material (9.5 ×10⁻⁶/K) were successfully prepared by the solidification method. The fracture toughness of the composite toughened sample is 2.25 times higher than that before toughening, which exceeds most of the current low-thermal conductivity ceramics.     

Solvothermal-derived multicomponent rare-earth cerate ceramics toward remarkable thermophysical properties

The multicomponent rare-earth cerate (Y_0.2La_0.2Nd_0.2Sm_0.2Eu_0.2)₂Ce₂O₇ (5RE₂Ce₂O₇) ceramics were successfully fabricated through solvothermal method and the following calcination process. The microstructure and phase composition of the as-obtained products were systematically characterized via SEM, TEM and XRD techniques. The results showed that the as-synthesised 5RE₂Ce₂O₇ has a single-phase fluorite-type crystal structure with the particle size of approximately 200 nm. Furthermore, the as-synthesised 5RE₂Ce₂O₇ demonstrated lower thermal conductivity (1.9–1.26 W m^?1·K^?1 at 25–1000 °C), higher thermal expansion coefficients (CTEs, 12.48 × 10^?6 K^?1 at 1000 °C), and outstanding mechanical properties including large Young's modulus (248.0 ± 0.35 GPa) and high fracture toughness (2.4 ± 0.21 MPam^1/2). The excellent properties of the as-synthesised 5RE₂Ce₂O₇ demonstrates its potential application as a new type of next-generation TBCs.     

Effects of Yb and Sc co-doping on the thermal properties and CMAS corrosion of garnet-type (Y3-xYbx)(Al5-xScx)O12 ceramics

Thermal barrier coatings with excellent thermal performance and corrosion resistance are essential for improving the performance of aero-engines. In this paper, (Y_3-xYb_x)(Al_5-xSc_x)O₁₂ (x = 0, 0.1, 0.2, 0.3) thermal barrier coating materials were synthesized by a combination of sol-gel method and ball milling refinement method. The thermal properties of the (Y_3-xYb_x)(Al_5-xSc_x)O₁₂ ceramics were significantly improved by increasing Yb and Sc doping content. Among designed ceramics, (Y_2.8Yb_0.2)(Al_4.8Sc_0.2)O₁₂ (YS-YAG) showed the lowest thermal conductivity (1.58 Wm^?1K^?1, at 800 °C) and the highest thermal expansion coefficient (10.7 × 10^?6 K^?1, at 1000 °C). In addition, calcium-magnesium- aluminum -silicate (CMAS) corrosion resistance of YS-YAG was further investigated. It was observed that YS-YAG ceramic effectively prevented CMAS corrosion due to its chemical inertness to CMAS as well as its unique and complex structure. Due to the excellent thermal properties and CMAS corrosion resistance, YS-YAG is considered to be prospective material for thermal barrier coatings.     

Crystal structure and microwave dielectric properties of (Mg0.2Ni0.2Zn0.2Co0.2Mn0.2)2SiO4 - A novel high-entropy ceramic

Novel (Mg_0.2Ni_0.2Zn_0.2Co_0.2Mn_0.2)₂SiO₄ (A5SO) high-entropy microwave dielectric ceramics with olivine structure were prepared in the sintering temperature range of 1100 °C–1300 °C via the solid-phase reaction route. The crystal structure was confirmed by XRD, Raman, and Rietveld refinement. Optimal microwave dielectric properties (ε_r = 8.02, tanδ = 0.00051 at 14.5 GHz, and τ_f = ?38.2 ppm/°C) were obtained at the sintering temperature of 1250 °C, where a relative density of 95.1% was detected. The complex chemical bonding theory manifests that the ε_r value of A5SO is mainly affected by the ionicity of A-O (A = Mg, Ni, Zn, Co, Mn) bond, while the dielectric loss is affected by both A-O and Si–O lattice energy. The τ_f value is mainly influenced by the [A(2)O₆] oxygen octahedral distortion (1.8 × 10^?3). The experimental results of this study provide both theoretical and practical guidance for high-entropy microwave dielectric ceramic applications.     

A novel high-entropy monoboride (Mo0.2Ta0.2Ni0.2Cr0.2W0.2)B with superhardness and low thermal conductivity

A new high-entropy monoboride (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic with a WB-type orthogonal structure was designed and synthesised by in-situ reactive hot pressing at 2000 °C and 30 MPa for 1.5 h under an argon atmosphere. The microstructure of the sintered samples was comprehensively characterised, and the formation of a high-entropy monoboride (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic was confirmed. Owing to the high density of the dislocations and strengthening metal-boron bonds, the high-entropy (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic exhibited a hardness of 48.51 ± 4.07 GPa, which enabled it to be classed as a new superhard material. In addition, the thermal conductivity (2.05 ± 0.10 W/(m·K) at 400 °C) and electric conductivity (132.30 S/cm) were determined.     

Novel high entropy (Y0.2Sm0.2Gd0.2Er0.2Ho0.2)3NbO7 nanofibers with ultralow thermal conductivity

Thermal insulation materials can provide thermal protection in extreme environments. Ceramic fibers have played an important role in the thermal protection field at high temperatures due to the advantages of low density, high strength, low thermal conductivity, and excellent thermal stability. In this work, high entropy (Y_0.2Sm_0.2Gd_0.2Er_0.2Ho_0.2)₃NbO₇ (5RE₃NbO₇) nanofibers were fabricated by electrospinning and subsequent calcination. Defective fluorite-structured 5RE₃NbO₇ nanofibers were obtained when heated at 900°C. The research indicates that 5RE₃NbO₇ nanofiber based porous ceramics present an ultralow thermal conductivity (0.0992 W/m·K, porosity of 78.18%), good thermal stability, and high spectral reflectance, which establish the foundation for applications in thermal insulation.     

A new type of Sr(Zr0.2Hf0.2Ce0.2Yb0.2Me0.2)O3−x (Me = Y,Gd) high-entropy ceramics used in thermal barrier coatings

Seeking for new ceramics with excellent thermophysical properties as thermal barrier coatings candidate materials has become a hot research field. In this study, Sr(Zr_0.2Hf_0.2Ce_0.2Yb_0.2Me_0.2)O_3−x high-entropy ceramic powders were successfully synthesized by the method of solid-state reaction, and the ceramics with single phase were prepared by pressureless sintering at 1600°C. The phase composition, microstructure, element distribution, high-temperature thermal stability, and thermophysical properties of the ceramics were studied. The results showed that Sr(Zr_0.2Hf_0.2Ce_0.2Yb_0.2Me_0.2)O_3−x ceramics were composed of SrZrO₃ phase and the second phase of AB₂O₄ spinel (i.e., SrY₂O₄ and SrGd₂O₄). The content of the second phase was gradually increased after heat treatment at 1400°C, which significantly improved the thermophysical and mechanical properties of the ceramics. The microhardness and fracture toughness of the ceramics were improved compared with that of SrZrO₃. The thermal conductivities of Sr(Zr_0.2Hf_0.2Ce_0.2Yb_0.2Me_0.2)O_3−x (Me = Y, Gd) ceramics were 1.30 and 1.28 W m⁻¹ K⁻¹ at 1000°C, which were about 35% and 40% lower than that of SrZrO₃ (1.96 W m⁻¹ K⁻¹) and yttria-stabilized zirconia (2.12 W m⁻¹ K⁻¹), respectively. The thermal expansion coefficients of Sr(Zr_0.2Hf_0.2Ce_0.2Yb_0.2Me_0.2)O_3−x (Me = Y, Gd) ceramics were 12.8 × 10⁻⁶ and 14.1 × 10⁻⁶ K⁻¹ at 1300°C, respectively, which was more closer to the superalloys compared with SrZrO₃ ceramic (11.0 × 10⁻⁶ K⁻¹).     

Phase evolution and thermophysical properties of high-entropy RE2(Y0.2Yb0.2Nb0.2Ta0.2Ce0.2)2O7 oxides

Pursuing novel thermal barrier–coating materials with lower thermal conductivity and high-temperature stability can simultaneously improve the working efficiency and service temperature of a gas turbine. In this study, a series of high-entropy RE₂(Y_0.2Yb_0.2Nb_0.2Ta_0.2Ce_0.2)₂O₇ (RE = La, Nd, Sm, Gd, Dy, and Er) oxides were prepared though solid-state reaction. Through tuning the rare-earth cations, an order–disorder transition occurs from certain partially ordered weberite structure (C222₁) to disordered defective fluorite structure (Fm$\overline{3}$m). All the high-entropy RE₂(Y_0.2Yb_0.2Nb_0.2Ta_0.2Ce_0.2)₂O₇ oxides possess low thermal conductivity in the range of 0.91–1.34 W m⁻¹ K⁻¹ at room temperature, which can be attributed to increased lattice anharmonicity and disorder, resulting in additional phonon scattering. Herein, we proved that the incorporation of heterovalent cations at B-sites in high-entropy A₂B₂O₇ crystals is an effective strategy to reduce the thermal conductivity without compromising the decrease of oxygen vacancy. Moreover, the high-entropy RE₂(Y_0.2Yb_0.2Nb_0.2Ta_0.2Ce_0.2)₂O₇ oxides show the relatively higher thermal expansion coefficients of 10.3–10.7 × 10⁻⁶°C⁻¹ and excellent phase stability at elevated temperatures.